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Document DEVICE REPORTRadio-Electronics-1970-10cuy 4-cimniici sterco tcchnhiiocs build FM stereo multiplex 11enctatiw Pro's tape reawding quiz Special Get better sound from your stereo Issue Stereo 1971 1. 01../ modular 6-cI.;ii.u,eI stereo mixer urcan.i 6ERNSBACK PUBLICATION performance *Audio magazine says: "It is extremely attractive with its base and dust cover, both of which are optional accessories, and it performs superbly. In over twenty hours of use, the unit performed flawlessly, with never a fault in its changing operations during that time. Naturally, we cannot test any equipment to destruction and still produce a number of profiles each month. However, Garrard's reputation practically guarantees continued high-quality performance for years, and any user should be completely satisfied with this model, which represents the culmination of many years of turntable manufacture." Price * *Stereo Review says: "At a time when most automatic turntable prices are soar- ing, it is encouraging to note that the price of the SL95B is unchanged from that of the SL95 ($129.50) . A number of different bases are available ranging in price from $6.50 to $19.95. A dust cover that fits all bases is $6.50." Unbeatable combinatio n * Reprinted with permission from the March 1970 issue of Audio© ** Reprinted with permission from the March 1970 issue of Stereo Review © Garrard's SL95B Automatic Turntable $129.50. . For literature write Garrard, Westbury, N.Y. 11590 British Industries Co. Circle 1 on reader service card Put More "GO POWER" into Your Electronics Career MCD17 hL hi) JI1 from Technician to by studying at home with Orantljam Stilool of engineering bas contareS on ofjn Qoe gsoociate in Science in Cilrctronico Qnginuring bwrw..r.......n...m..mw.rr.amg.J. *gum hrttim.w.... .w. M 4 M. Immorrs ,:g r..h M1 .F+- gati.f.ClfLtödC_ IB[¢- GRANTHAM SCHOOL OF EN GIN E ERI N G "the college that comes to you" Earn a DEGREE in Electronics Engineering The GRANTHAM educational program in ELECTRONICS ENGINEERING is designed to upgrade electronics technicians to the engineering level, mostly by home study. While you continue your present employment, you can really learn electronics engineering and earn an ACCREDITED DEGREE. Upgrade your income and prestige by upgrading your electronics education at the college level. GRANTHAM'S strong- foundation educational program in electronics engineering is designed especially for the working technician. This program, offered mostly by home-study, leads to non-obsolescent skills -to skills based on reasoning -and leads to the DEGREE of Asso- ciate in Science in Electronics Engineering (the ASEE Degree). This accredited degree program consists of four "correspondence semesters" of 100 lessons each, a total of 400 lessons. All except the last ten of these lessons are completed entirely by correpondence. However, after you have completed Lesson 390 you must then attend a two-week Graduation Seminar at the School. It is during this attendance that you complete Lessons 391 thru 400 and receive your ASEE Degree. Accreditation and G.I. Bill Approval Grantham School of Engineering is accredited by the Accrediting Commission of the National Home Study, is approved under the G.I. Bill, and is authorized under the laws of the State of California to grant academic degrees. Grantham School of Engineering 0-r ED Established in 1951 s NHSC o'c' 1505 N. Western Ave. II z Hollywood, Calif. 90027 ;¿ bpMËS,rO a 00 Telephone: (213) 469 -7878 Earn Your FCC License Along the Way You have heard and read, over and over again, about how important an FCC license is to your success in electronics. It is true that an FCC license is important- sometimes essential -but it's not enough ! Without further educa- tion, you can't make it to the top. Get your FCC license without fail, and then continue your electronics education to earn your degree. It makes good sense to prepare for your FCC license with the School that includes the FCC license preparation as an incidental part of your degree program. In the Grantham ASEE Degree program, FCC -license and radar -endorsement preparation are integrated into the first two semesters for the benefit of those students who have never obtained such a license. Find out how you can advance in electronics Mail the coupon below for our free Bulletin r- Grantham School of Engineering RE-10-70 1505 N. Western Ave., Hollywood, Calif. 90027 Gentlemen: Please mail me your free Bulletin which explains how the Grantham educational program can prepare me for my FCC license and Associate Degree in Electronics Engineering. I understand no salesman or counselor will call. Name Address City State I have been in electronics for Zip years. Circle 2 on reader service card www.americanradiohistory.com Volume 41 Number 10 NEW &TIMELY ... RADIO- ELECTRONICS FOR MEN WITH IDEAS IN ELECTRONICS October 1970 The FERPICS are Coming MURRAY HILL, N.J. -Think of an erasable, reusable 35-mm slide on which an operator can electronically erase all or part of the image, add new material, and reproject a new image on the screen. Scientists at Bell Laboratories are investigating these devices which store images until they are electronically erased or changed. Called ferpics (ferroelectric ceramic picture devices), the devices are made of material first announced by Sandia Corporation. The ferpic device is a sandwich structure consisting of transparent electrodes, a photoconductive film and a thin plate of fine-grained ferroelectric ceramic. To change an image is stored in the form of variations of transparency across the film. In a ferpic the image is stored as a variation of the "bi- refringence" of the ceramic plate -as a variation in the way the plate transmits polarized light. In one mode of oper- ation, a scanned laser beam records an image on the photoconductive film-one pic- ture element at a time as in a TV picture. A voltage applied to the transparent electrodes develops a field across the ce- ramic. When the field is re- moved, the image remains stored on the ceramic plate. The image store in the fer pic device can be viewed by putting light polarizing sheets FERPIC FOCUS ADJUSTMENT is made by Juan Maldonado on image of Bell System symbol projected onto small screen. the stored information in this simple structure, a new technique, called "strain- biasing" was developed at Bell Labs. The basic ferpic sandwich is bonded to a transparent substrate which is then flexed so as to stretch or "strain" the material. In an ordinary film slide over it, or the image can be projected on a screen using polarized light in a conventional projection system. To erase the image, the entire structure is flooded with light in the presence of a reversed electric field; the plate is then ready to store another image. 2 HANDFULL OF MEMORIES-Ann Karagines examines 250 feet of magnetically plated Mini -Wire at Honeywell's Aerospace Division in St. Petersburg, Florida. The wire, which is only two thousandths of an inch in diameter, has been combined with medium-scale integrated circuits in a new computer memory being tested al, the division. The device is being explored in the hope of obtaining efficient, low-cost solid state information displays with features that are difficult to obtain in present display systems. Because the image stored in the ferpic ORIGINAL ?HOT() (above) is conventional photo. FERPIC STORED IMAGIE (below) shows loss of detail and clarity. device can be projected, very large displays can be obtained. Also ferpic slides can retain images for a long time without electrical power. A TV set must be fed signals continuously to retain an image; once power stops, the image fades. At the present stage of development ferpic devices can store and display, with high resolution, black and white images that fade only slowly. Thus present ferpics are suitable for the display of, for example, written text or figures, since such applications, while exploiting the unique image storage capabilities of the device, would not place severe demands on the speed or lifetime of the ceramic material. Faster Fax -A SADDLE BROOK, N.J. new, low cost, high speed facsimile telecommunications unit that can cut telephone costs by as much as one-half has been in- troduced by Magnavox Sys- tems, Inc. Called Magnafax 860, the new unit is a two - (continued on page 12) RADIO- ELECTRONICS www.americanradiohistory.com Radio -Electronics. F O R M E N W I T H I D E A S I N ELECTRONICS October 1970 Over 60 Years of Electronics Publishing HI -FI STEREO AUDIO New 4-Channel Stereo Techniques . . . . 33 The late.st nvorcl on the newest .sound Get The Most Out Of Your Stereo System , 40 What you can do to stake your system better How To Buy Audio Tape 43 All recording tape is not the same Constant -Speed Motors For Tape Recorders 49 Hysteresis -synchronous for better speed control Tape Recording Facts And Falacies 53 Check your tape recording awareness Walter Salm . . . . Peter Sutheim Byron Wels Al Williams .. David K. Kirk 4- Channel Stereo is here. Take a careful look at the latest developments in this exciting area. . . . see page 33 BUILD ONE OF THESE Six -Channel Stereo Mixer -Preamp 36 Modo/tir sOlial-state unit does most and tliiJig Low -Cost FM Stereo Multiplex Generator 63 . . George Hanchett Al Franson /decd for setting up .solid -salve receivers In The Shop Ripple and noise Modular TV Sets Chart Kwik -Fix Troubleshooting Charts 4 -types of focus stages R -E Reference Manual How to install TV antennas Service Clinic Solutions to reader problems TELEVISION 24 Jack Darr 44 . Stanton R. Prentiss 45 ,Forest H. Belt 58 James A. Gupton, Jr. 84 Jack Darr 4 LAYER DIODE SCR SCS PUT How to Use the PUT (programmable unijunction transistor). Try some of these circuits. . . . see page 50 GENERAL ELECTRONICS Looking Ahead , 4 . David Lachenbruch Current happenings with ftattue overtones Editorial 6 Veteran's benefits for technical courses Equipment Report 26 Jack Darr Heathl,it 1G -57 postmarker .sweep generator How To Putter With The PUT 5O R W Fox Try these circuits awing the programmable unijunction transistor Blueprint For Progress 68 L. L. Farkas Your future in the electronics industry DEPARTMENTS Stereo Mixer Preamp is solid -state dream unit. If you make tape recordings you need one. . . . see page 36 CB Troubleshooter's Casebook Coming Next Month Correspondence 76 82 New & Timely New Books 16 New Literature 2 New Products, 70 48 New Semiconductors. 87 75 Noteworthy Circuits 92 RADIO- ELECTRONICS, OCT. 1970. Vol. 41, No. 10 Published monthly by Gernsback Publications, inc., at Ferry St., Concord. N. H. 03302 Editorial. Advertising, and Executive peaces, 200 Park Ave. S., New York, N.Y. 10003. Subscription Service: Boulder, Colo. 80902. l'an -SAemcoenrdic-acnlascsoupnotsriteags.e paid at Concord, N. $7. Other countries, 11. Printed in U.S.A. One -year subscription rate: U.S. and 07.511, single espies 000. ('t 1070 by Gernsback Publications, possessions. Canada. $6. Inc. All rights reserved. POSTMASTER: Notices of undelivered copies (Form 3579) to Boulder. Colo. 80302. Radio -Electronics is indexed in Applied Science & Technology Index (formerly Industrial .arts Index) www.americanradiohistory.com LOOKING AHEAD Volume 41 Number 10 RADIO -ELECTRONICS . . . FOR MEN WITH IDEAS IN ELECTRONICS October 1970 by DAVID LACHENBRUCH CONTRIBUTING EDITOR Technicians and X -rays A little-publicized survey by the U.S. Department of Health, Education and Welfare so far has indicated that there may be no grounds for fears that service technicians are exposed to excessive amounts of X- radiation from color television receivers. The tests are being conducted with the cooperation of technicians in Baltimore. At press time, surveys had been completed in about 50 shops and HEW was hoping to enlist about 50 more. In the tests, technicians used a new type of dosimeter to determine their exposure to radiation. The tiny instruments were mounted in eyeglass frames, on finger rings and on belts, to measure radiation exposures at various vital points of the body. At the halfway point in the tests, Dr. Robert L. Elder, acting director of HEW's Division of Electronic Products, Bureau of Radiological Health, told us that analysis of the dosimeters showed "no significant exposure" to radiation of technicians servicing color sets. "To date there has been no radiation which warrants action." -at Dr. Elder also said that the survey showed that tech- nicians were being extremely diligent least in Balti- more-in checking high -voltage in every service job and setting it to the manufacturers' specifications. How about the U.S. Surgeon General's admonition to "sit 6 to 10 feet away from color TV sets?" Dr. Elder indicated that this rule is being modified slightly with the improvement in new color sets, less radiation-prone replacement parts and good radiation discipline by technicians. "It's a guide, not a mandate," he said. To those who inquire, HEW is saying: "If you are concerned about possible radiation, sit 6 to 10 feet away and call a service technician." Causes of radiation While we're on the subject, another HEW study has found that the "predominant cause of X- radiation" in color sets is excessive high voltage on the picture tube. HEW made lab studies of sets which flunked factory radiation tests between June and September 1969 (there were 22 of them) . The studies showed that none of the sets emitted excessive radiation when the high voltage was held down to the manufacturer's suggested maximum. On the basis of preliminary data, the studies indicated that Japanese -made color tubes "may be more poorly shielded than their American counterparts." Since the tests were made, Japanese glass manufacturers have increased the X -ray resistant content of their tube envelopes. 1970 TV -model sales There's a recession on, but it hasn't affected total TV sales as much as you might think. Sales of 1970 model television sets totaled about 11.9 million units, only five percent below the record 12.55 million 1969 models sold. Of course, the difference was that black-and-white sales went up (about six percent) while color sales declined (16 percent) from the 1969 model year. And within the color category, portables-particularly foreign-made-accounted for a far greater percentage of sales than ever before. Color sets carrying American manufacturers' brand names declined by 18 percent in the 1970 model year, while U.S. -brand monochrome sets dipped 14 percent. On 4 the other hand, so- called "foreign brand" imports (sets without American manufacturers' names on them) increased their sales 12 percent in color and a big 170 per- cent in black- and -white during the 1970 model year. Another videoplayer system A dark -horse entry in the home videoplayer sweepstakes could be ABTO Inc. This firm, jointly owned by American Broadcasting Companies and Technical Operations Inc., was originally formed to sell to television stations an optical process which permits the recording and playback of color programming on black- and-white motion picture or slide film. ABTO now is discussing a home version, in which a color television set would use a film-scanning system to produce color from low-cost Super-8 monochrome film cartridges. As an added plus, the TV-film player would be able to show conventional color home movies on a color TV screen. ABTO is interested in marketing the film system only, not the hardware. Higher speed facsimile Relatively low -cost facsimile systems which use regular voice telephone lines now have become accepted items of equipment in many offices, large and small. Their major drawback, particularly where long- distance telephone lines are used, heretofore has been their slow speed -normally six minutes to transmit one 81/2-x -11 -inch page. But now a speed -up is coming. The first to announce a faster office fax machine available for sale has been the Magnavox Corporation (see New & Timely, this month, for full details). Other high -speed machines are on the way. Xerox is expected soon to introduce a 4-minute version of its 6minute Telecopier. Comfax is developing a somewhat more elaborate machine which can transmit and receive a standard letter-size page in as little as 90 seconds. TV fires evaluated How big a problem is posed by burning television receivers? National Electronics Association has released re- sults of a survey of its own service technician members which differ rather sharply from the "clear- and -present- danger" philosophy expressed in the recent report of the National Commission for Product Safety, NEA's survey covered the period of January 1 to March 30, 1970, but was projected to cover the entire United States. On the basis of its survey, NEA made these projec- tions: Some 4,000 television failures occur each year which show signs of combustion. Only about 20% of these, or 800, involve any fire which is not contained within the cabinet. With some 87 million TV sets now in use, the figure comes to less than one one -thousandth of one per- cent. Any TV set fire is one too many, but NEA's data seems to indicate a good safety record considering the number of sets in use and the amount of time the average family wends with the TV set. NEA gave this breakdown of the causes of television set fires: On-off switch area, 38% ; high-voltage and hori- zontal- output transformer area, 33%; short - circuits caus- ing power-supply overloads, 13 %; miscellaneous, 16 %. Since the report of the National Commission on Product Safety, Underwriters' Laboratory and the television manu- facturing industry have developed new and tighter fire safety standards for receivers and components. R -E RADIO- ELECTRONICS www.americanradiohistory.com Keep electronic corrponents handy with Mallob nR Benchtop Organizers Eaci Mallobin contairs a popular assortment of electronic compoients in a stackaole, in erloc< ng plastic case. Fifteen partitioned drawers keep parts neat. And each drawer is color coded and labelec for quic< locaticfr of the part you want. Mallobins come with selectec compoients including all types cf fixed capacitors, LIOL and wire -wound resistors, carbon and wire -wound controls. In addition to regular Mallcbins, custom assortments a-e available Ask your Mallory cistributor for Mallobin pr ces and details today. MALLORY aSdzivi1s5io5n8 of P. R MALLORY & CO. INC. fnditan- wolfs. Indiana A1206; Telephone. 317 -ß,-0-5353 Batteries Capacitors Casse-te Tapes CoWis Resistors Semiconductors Sonalsrto Sw tches . Timers Vibrators OCTOBER 1970 Circle 3 on reader service card 5 www.americanradiohistory.com Editorial Veterans Educational Benefits If you're a recent veteran, there are many kinds of educational benefits that are available to you. They are particularly important if you wish to increase your knowledge of electronics. Through the Veterans Administration it is possible to obtain up to $175 per month for 36 months ( a grand total of $6400 ), to use toward your further education in electronics. This applies to both resident and home -study ( correspondence ) courses. If you now know nothing about electronics, you can start with a basic course and go on through whatever specialty interests you. If you are already at the technician level, you can take specialized courses in communications, radar, broadcasting, computers, etc. As long as the school is approved ( check with your local Veterans Administration Office ) you will be entitled to financial assistance. In all instances, the school offering the course you are interested in can tell you if it is approved by the VA. They can also spell out the exact benefits you can expect to receive. A reminder; in many instances these benefits will cover the complete cost of a correspondence course. So if you can't attend a resident school, don't write off further education as impossible. If you do take a correspondence course, all electronic equipment normally supplied with the course is included and is yours to keep. Don't let this opportunity pass you by. These benefits are available to you for a limited time after your discharge from military up now. service. If there's a school you want to It's your future-get the training you attend, follow need to make it the most of it. Radio -Electronics HUGO GERNSBACK (1884-1967) founder M. HARVEY GERNSBACK, editor and publisher LARRY STECKLER, managing editor Robert F. Scott, W2PWG senior technical editor Jack Darr, service editor I. Queen, editorial associate Matthew Mandl, contributing editor David Lachenbruch, contributing editor Joan Washington, editorial assistant Vincent P. Cicenia, production manager Barbara Rosefelt, production assistant H. Matysko, circulation Cover by Harry Schlack 6 RADIO- ELECTRONICS is published by Gernsback Publications, Inc. 200 Park Ave. South New York, N.Y. 10003 (212) 777 -6400 President: M. Harvey Gernsback Secretary: Bertina Baer ADVERTISING SALES EAST Stanley Levitan, Eastern Sales Mgr. N.Y.C. (212) 777 -6400 MIDWEST/Texas/Arkansas/Okla. Ralph Bergen, 6319 N. Central Ave. Chicago, Ill. 60646 (312) 792 -3646 PACIFIC COASTíMountain States ). E. Publishers Representative Co., 8560 Sunset Blvd., Suite 601 Los Angeles, Calif. 90069 (213) 659 -3810 420 Market St. San Francisco, Calif. 94111, (415) 981 -4527 SOUTHEAST E. Lucian Neff Associates 25 Castle Harbor Isle Fort Lauderdale, Florida 33308 (305) 566 -5656 SUBSCRIPTION SERVICE: Send all subscription orders and correspondence to RADIO-ELECTRONICS, Subscription Department, Boulder, Colo. 80302. MOVING? For change of address, allow six weeks, furnishing both the old and new addresses and if possible attaching label from a recent issue below. Otherwise please print clearly your name and address exactly as it rappears on your label. ATTACH LABEL HERE L_ name (please print) address city state zip code Mail to: RADIO-ELECTRONICS SUBSCRIPTION DEPT., BOULDER. COLO. 80302 Circle 4 on reader service card 0. www.americanradiohistory.com There wasn't room for a big improvement. So we made a little one. Our engineers made three changes in Sony's popular PS- 1800 playback system. They added a little button called "Automatic/Manual"; streamlined its appearance and added "A" after the PS-1800. Obviously, none of these, earthshaking changes. You might never use the little button labeled "Automatic /Manual," unless you ran across a non -standard record where the recorded material goes too far into the normally "dead" space surrounding the label. Such records are few and far between. If you run up against one of them, the automatic tonearm return on the Sony would ordinarily lift and return just before the record's end. However, if you push the button to 'Manual" the arm will track the entire record until you lift it off by hand (or push the reject button). The styling change means that this superb playback instrument will enhance any room. And the "A" will help you identify it as the new model when you visit your hi-fi specialist What's more important is what our engineers didn't do to the PS-1800; what they left well enough alone. The servo control DC motor that keeps wow and flutter at an inaudibly low 0.08; rumble down 60dB (ARLL). A variable pitch control from ±4% (if you don't need it, the built -in strobe disc assures that the variation is indeed tuned out). And the balanced, low mass tone arm is capable of tracking virtually any cartridge at its lowest recommended tracking force. Not to mention the automation system, which uses a remarkable new solid -state device, the Sony 'Magnetodiode (SMD). Automatically, it lifts and returns the arm without imposing any drag or the arm during play. The SMD eliminates a variety of mechanical linkages formerly neces- sary for this function. And there's a reject button (on the front panel so you don't have to lift the dust cover to get at it). The price of the PS- 1800A? No change. $199.50 (suggested list), includes turntable, arm, base and dust cover (cartridge not included). Sony Corporation of America, 47-47 Van Dam Street, Long Island City, New York 11101. SONY®PS-1800A www.americanradiohistory.com GET A FASTER START IN THE COURSE YOU CHOOSE WITH NRI'S REMARKABLE ACHIEVEMENT KIT Learning electronics at home is faster, easier, more When you enroll with NRI we deliver to your door everything you need to make a significant start in the Electronics field of your choice. This remarkable, new starter kit is worth many times ... the small down payment required to start your training. And it is only the start only the first example of NRI's unique ability to apply 50 years of home-study experience to the challenges of this Electronics Age. Start your training this exciting, rewarding way. No other school has any- thing like it. What do you get? The NRI Achievement Kit includes: your first set of easy- to -understand "bite- size" texts; a rich, vinyl desk folder to hold your training material in orderly fashion; the valuable NRI Radio -TV Electronics Dictionary; important reference texts; classroom tools like pencils, a ball -point pen, an engineer's ruler; special printed sheets for your lesson an- swers -even a supply of pre- addressed envelopes and your first postage stamp. interesting with new achievement kit Only NRI offers you this pioneering method of "3 Dimensional" home-study training in Elec- tronics, TV-Radio ... a remarkable teaching idea -in unlike anything you have ever encountered. Founded more than half a century ago the days of wireless -NRI pioneered the "learn -by- doing" method of home-study. Today, NRI is the oldest, largest home-study Electronics school. The NRI staff of more than 150 dedicated people has made course material entertaining and easy to grasp. NRI has simplified, organized and - dramatized subject matter so that any ambitious man regardless of his education -can effec- tively learn the Electronics course of his choice. DISCOVER THE EXCITEMENT OF NRI TRAINING Whatever your reason for wanting knowledge of Electronics, you'll find the NRI "3 Dimensional" method makes learning exciting, fast. You build, test, experiment, explore. Investigate NRI training plans, find out about the NRI Achievement Kit. Fill in and mail the postage -free card. No salesman will call. NATIONAL RADIO INSTITUTE, Electronics Division, Washington, D. C. 20016 8 RADIO-ELECTRONICS www.americanradiohistory.com ELECTRONICS COMES ALIVE AS YOU LEARN BY DOING WITH CUSTOM TRAINING EQUIPMENT Nothing is as effective as learning by doing. That's why NRI puts so much emphasis on equipment, and why NRI invites comparison with equipment offered by any other school, at any price. NRI pioneered and perfected the use of special training kits to aid learning at home. You get your hands on actual parts like resistors, capacitors, tubes, condensers, wire, transistors and diodes. You build, experiment, explore, discover. You start right out building your own professional vacuum tube voltmeter with which you learn to measure voltage and current. You learn how to mount and solder parts, how to read schematic diagrams. Then, you progress to other experimental equipment until you ultimately build a TV set, an actual transmitter or a functioning computer unit (depending on the course you select). It's the practical, easy way to learn at home -the priceless "third dimension" in NRI's exclusive Electronic TV-Radio training method. SIMPLIFIED, WELL- ILLUSTRATED "BITE- SIZE" LESSON TEXTS PROGRAM YOUR TRAINING Lesson texts are a necessary part of training, but only a part. NRI's "bite- size" texts are as simpli- fied, direct and well -illustrated as half a century of teaching experience can make them. The amount of material in each text, the length and design, is precisely right for home -study. NRI texts are programmed with NRI training kits to make things you read come alive. As you learn, you'll experience all the excitement of original discovery. Texts and equipment vary with the course. Choose from major training programs in TV -Radio Servicing, Industrial Electronics and Complete Communications. Or select one of seven spe- cial courses to meet spe- cific needs. Check the courses of most interest to you on the postage -free card and mail it today for your free catalog. Available Under NEW GI BILL If you served since January 31, 1955, or are in service, check GI line in postage -free card. custom training kits "bite-size "texts OCTOBER 1970 11 www.americanradiohistory.com only MASTER offers you 32choices, jr > 411, Choose your combina- tion : with or without switches and safety 400 shields ... four different wattages ... 120 or 230. volts. Snap -in, rugged ceramic elements are encased in stainless steel, easily changed in seconds. Compressed air or inert gas concentrates precisely controlled heat up to 1000° exactly where you want it. The perfect tool at an unbeatable price ... as low as $75! Send for your Complete FREE Catalog of flameless Heat Guns, Blowers and Torches. New &Timely (continued from page 2) speed model which offers the user the option of a 3 minute or 6 minute transmission for full -page documents (drawings, proofs, financial and priority reports, photographs) through a telephone coupling. The two -speed model offers a significant reduction in both telephone line charges and operator time while operating in the 3-minute setting, and the 6- minute mode provides improved resolution and picture quality. In addition, the 6-minute setting permits the Magnafax 860 to speak to a wide number of facsimile de- vices installed in the USA. * Teleconsultation Is Now MASTER TV PSYCHIATRIC CONSULTATION shows how system will operate in Boston. Racine, WI 53403 Circle 5 on reader service card PROGRAM BOSTON, MASS.-Television now links two large Greater Boston teaching hospitals in a way never attempted anywhere before. Massachusetts General Hospital in Boston and the Veterans Administration Hospital, 25 miles away in Bedford, YOUR share their expertise over closed-circuit television. The unique venture embraces all three purposes of each institution: AUDIO SYSTEM c10-20A WITHOUT EXTENSIVE WIRING THIS HIGH DENSITY MATRIX SELECTOR SWITCH eliminates hundreds of soldered joints and hours of labor when you pre -program, select monitor audio systems or insert components in breadboarding circuits. Useful in applications from EKG equipment to water sprinkler time control systems; also in electrical component testers, numerical control for machine tools or to control, transmit and receive frequency. patient care, physical education, and research. Dr. John H. Knowles, General Director of the MGH, and John J. Whalen, Director of the V. A. Hospital, primarily a psychiatric institution, announced the project recently. Newsmen watched a program beamed between the two hospitals. After a successful pilot period of two months, the project is now open on a regular basis. THIS COUPON WORTH $10.00 OFF REGULAR $25.00 PURCHASE PRICE OF A C10 -20A Mail this coupon and get a C10-20A Matrix Selector Switch with 100 crosspoints for only $15.00 postpaid. (Regularly $25.00) No COD's. Check or money order must accompany order. MAIL TODAY! OFFER LIMITED CHERRY CHERRY ELECTRICAL PRODUCTS CORP. 3618 Sunset Avenue, Waukegan, Illinois 60085 The psychiatrist and patient at Bedford will also be able to see whoever is at the MGH Teleconsultation room. The two -way nature of the system enables either of the two hospitals to seek medical or allied medical consulta- tions. Residents in training at MGH-in dermatology, for example-with their instructor will be able to see skin disorders that would be rare or non-existent to MGH. At the same time, the Bedford patient will gain by the consultation that NAME_ ADDRESS CITY is part of the demonstration. And, an engineer at the MGH could examine a chart shown by an engineer at Bedford in addition to hearing a word description STATE ZIP of a hospital engineering program. Medical and non -medical teaching programs Circle 6 on reader service card 12 (continued on page 14) Circle 7 on reader service card www.americanradiohistory.com ANY NUMBER CAN PLAY. The time is tomorrow. The name is TEAC. The machines are the Simul-trak' Series TCA-40. And they're here today. This series of tape decks combines the best features of high -quality quarter-track, two-channel operation with four -channel stereo capability. It's the best of two worlds, in three versions, four channels. All three models feature four-channel playback, as well as regular two-channel playback with auto reverse. What's more, Models 40 and 41 can be modified later to the full four-channel capability of Model 42, at moderate cost. Meanwhile, any one of these machines is compatible with your present equipment; no modifications or reassembly are necessary. So what are you waiting for? - Simul-trak'" surrounds you with sound and gives you a headstart on tomorrow. TEAC, TEAC Corporation of America 2000 Colorado Ave. Santa Monica, Calif. 90404 General Specifications Speeds -71/2 and 33/4 ips Motors -1 hyst. sync., 2 outer rotors -±3 Wow and Flutter -0.12% @ 71/2 ips Freq. Response S/N Ratio -50 dB dB 50- 15,000 Hz @ 71/2 ips Crosstalk -48 dB tfCORO SEaECi it t.4M PEAY6ACI[ TEAC MOOEt RA.41 STEREO RECORD AMPIIR,ER TCrA- 40 1/4- track, 2- channel stereo playback, plus 4- channel stereo playback (in -line) 1/4-track, 2- channel erase and record heads for future "step-up Automatic reverse for uninterrupted playback of conventional 2-channel tapes Readily modified to TCA -41 or42 Built -in solid -state preamplifiers Ideal for duplication master or copy deck TC" 41 (iilu.s't rater?) 1/4- track, 2-channel stereo playback, plus 4-channel stereo playback (in -line) 1/4-track, 2-channel record Automatic reverse for uninterrupted playback of 2- channel tapes Readily modified to future 4 channel recording capability, or TCA -42 Solid -state playback and record preamplifiers Off-the-tape monitoring selector TCrA- 42 1/4- track, 4- charnel 2-channel stereo playback, plus 4-channel stereo record (in-line) Automatic reverse stereo playback (in -line) for uninterrupted playback 1/4 -track 2- channel of 2- channel tapes stereo record and Total of 8 separate sol id -state playback and record preamplifiers Off- the-tape monitor selectors www.americanradiohistory.com TRUE TRIGGERED SWEEP New &Timely OSCILLOSCOPE/VECTORSCOPE MODEL TO -50 DC to 10 mhz frequency response .02 volt sensitivity Calibrated vertical attenuator Calibrated time base Supplied with combination Direct /Lo -Cap probe 5 X magnifier Automatic triggering mode 5" flat face tube edge -lit graticule One Year Warranty 33950 Made in U.S.A. L See your distributor or write Dept. RE-10 LECTROTECH, INC. 4529 N. Kedzie Ave , Chicago, Illinois 60625 (continued from page 12) will also be developed between the two institutions. Physicians at the hospital - in Boston have examined some 1,700 patients at the airport since the system originated. Both airport employees and passengers have availed themselves of the ser- vice aimed at making optimal use of the busy physician's time by eliminating travel to the airport medical station. Late in the spring of 1969, Dr. Thomas F. Dwyer, an MGH psychiatrist, began interviewing psychiatric patients over the closed- circuit network. New Coast-Guard Radar-TV Circle 8 on reader service card FOR ALL FIRER POLICE SECURITY IlDUSTRIAL BUSINESUSE Model 2301 132 -174 MHz $37500 VHF -FM 1 CHANNEL 1 pair of crystals and 1 set of standard batteries. Model 2301A $47500 132 -174 MHz VHF -FM 2 CHANNELS 1 pair of crystals and 1 set of standard batteries Model 2302 450 to 470 MHz $59500 UHF -FM 1 CHANNEL 1 pair of crystals, 1 set of standard batteries and Tone. - Model 2303A $47500 32.5 -41 42 -50 MHz Available in 2 Frequency Ranges LF -FM 2 CHANNELS 1 pair of crystals. 1 set of standard batteries less tone` Model 2303A available with tone at additional charge. Professional performance! Perfec ly designed for efficient dependable and continuous heavy duty use. Provides instant voice contact with base stations mobile units and other portable transceivers Compatible with all 2 -way systems Receiver and transmitter operates on independent frequencies sensitive, noise immune souelch external connections for antenna, earphone and charger 1.6 watt output. FCC TYPE ACCEPTED & D.O.C. APPROVED -U.S. BUREAU OF MINES APPROVED 'SONAR RADIO CORPORATION 73 Wortman Avenue, Brooklyn, N.Y.11207 Please send information on the SONARCOM. Name Address City State Dept. 210 I 1 Zip Circle 9 on reader service card 14 -A WASHINGTON, D .C., new airborne search radar which converts radar infor- mation to daylight viewing will increase the U.S. Coast Guard's capabilities for small craft searches and rescues. The new system, called Search and Resale Airborne Radar, will be built by the AIL division of Cutler Hammer for the Coast Guard to detect objects as small as a 16 -foot fiberglas boat in five-foot seas at distances of 10 miles from the searching Coast Guard aircraft. The sys- tem is designed to detect these objects in clear weather as well as heavy fog and rain. The system will have a scanning an- tenna that will turn 300 revolutions per minute, a rate five times greater than that of today's operational radars. The resul- tant increase in radio beams, reflected by the consistency of the targets looked at. will reduce the interference from random objects in the ocean, such as wave crests which might normally appear on the radar scope as targets. Distinguishing this random "sea return" from small targets has been a major problem in the past. One of the most important features of the system will be the conversion of the radar information to a television screen. This will be the first development of a motion compensated system that con- verts radar blips to a TV type bright dis- play on board a flying aircraft. The relationship of small targets to other targets which appear on the radar screen will be accentuated because of a new design which takes the relationship of the input to the output amplifier loga- rithmically instead of linearly. R -E RADIO -ELECTRONICS www.americanradiohistory.com -;, , ¡ 007C4t7. ;!:rJ,l/:1¡_ ®S) u- I IIII iary4 4 " III --- ----. Want to tie. up the service market? Start with the Channel Master Opti -Vue Colo- CRT wi _h the three year warranty, ore TV set That needs a pict_ire tube, and one customer. -- ,Tay,r/O©/':<4 _----- N vfA.r :.D. 1]!..) -- ,Dl4©y f Tell Your customer how Opti -Vue guarantees the finest color he's ever seen for a full three year--not just one or two. And how, just in case something shot Id go wrong, he gets a free replacement. So it may :ost a little more, but it's worth it. And the price is right, too! Now, you've secu-ed the part of the sit he's most worried about he's sure to :all you when any other part fails. You've tied upall his service tusiness for a full three years by taking care of his knott est prob em, and, not unim- portantly, yoir custorrer's very happy with his new color vision! _._.-------' _- `"© So gc ahead and tie cne on with OPTI -VUE The line with 3 year warranty! CHANNEL MASTER Div. of Avnet, Inc., Ei:enville, N.Y. 12428 OCTOBER 1970 Circle 10 on reader service card 15 www.americanradiohistory.com ANNOUNCING An All New Crespondenie MIGHTY MITE Tube Tester Now Checks more tubes and it's faster than ever before with all solid state FET circuitry for instant on action . . . first time in tube tester history ew solid action push button function tches to speed up every test re is s n th famous encore Mighty Mite tube tester; it's updated and streamlined in appearance and performance. No more wasted time waiting for the tube tester to warm up when you have a hot troublesome tube in your hand ready to test. The TC154 Mighty Mite VI is instant-on with no meter drift. New FET circuitry still enables you to read grid leakage up to 100 megohms because it too is a high impedance device like a vacuum tube. New circuitry permits even higher sensitivity check on heater to cathode leakage; from 180,000 ohms to 300,000 ohms. The Mighty Mite still checks for shorts between each and every tube element with the famous stethescope shorts check. New two -toned vinyl- covered and brushed steel presents a truly professional instrument. See your Sencore distributor today and ask him for the new all solid state Mighty Mite. Only Sencore has it. Over 60,000 Mighty Mites now in use, Only $99.50 NO. 1 MANUFACTURER OF ELECTRON /C MAINTENANCE EQUIPMENT 3200 Sencore Drive, Sioux Falls, So. Dakota 57107 Circle II on render service cart! 16 HOW TO FIND PARTS I was sorry to read about John Sikara's complaint in the Correspondence Column about the difficulty in obtaining parts for construction arti- cles. I would like to suggest a method for the readers to find their parts. The first stop is, of course, their normal distributor from whom they can pick up all the standard parts. The second move is to find a distributor for the manufacturer of the parts they are missing. This usually can be done by checking the catalogues, yellow pages of the telephone book, or calling the nearest sales office or representative of that company. Then order the missing parts from that distributor. In some cases it may mean a delay of several weeks but the distributor can get the parts. If the parts still can not be pur- chased, then write directly to the company that makes them at the place they are made. The last resort, of course, is for the builder to write to the author in care of the magazine. RICHARD W. Fox Applications Engineer General Electric Company Auburn, New York, 13021 8-TRACK-DATA NEEDED - As a subscriber, I appeal to you or your readers for information-sche- matics and operating instructions covering 8 -track player/recorder manufactured by Kalof Electronics, Van Nuys, Calif. It is model U.T. 801, Se- rial No. D 1054. Will appreciate any information anyone has on subject player /recorder. BOB SPICER P. O. Box 191 Fort Gaines, Ga. 31751 OLD COPIES AVAILABLE I have several vintage copies of Radio News magazine, forerunner of RADIO -ELECTRONICS. Available are issues for the years 1924, '25, '26, '27 and '28. I have all issues for the year 1925 and one copy of the March 1940 issue. HAROLD DISHMAN Route 5 Maryville, Tenn. (continued on page 22) RADIO -ELECTRONICS www.americanradiohistory.com WE HAD JUST REPRINTED OUR LITERATURE . . . ... ADDING OUR FIFTH NEW PLANT . . . EN WE DID IT AGAIN PRECISION TUNER SERVICE 410015 Springfield, Mass. PRECISION TUNER SERVICE YOU vice can offer this specialized, expert service. Quality is our bag, man! Experienced, conscientious PTS Tuner Sercraftsmen with sophisticated, precision (and expensive) tools and equipment mean faster PROFIT for ou with PTS 8 -hour service No doubt about it! PTS mails your tuner back the SAME DAY it is received! Now less in- transit time, too! Precision ,and now with even shorter in- transit time! VHF or UHF $8.95 UV Combo's 40/41;s1915 Major Parts, Tubes, Transistors charged at Net Price CUSTOMIZED REPLACEMENTS AVAILABLE FOR $12.95 UP (NEW OR REBUILT) FIRST TO OFFER 365 -DAY GUARANTEE! - - - COLOR BLACK & WHITE TRANSISTOR TUNERS ALL MAKES - GUARANTEED COLOR ALIGNMENT NO ADDITIONAL CHARGE FREE JOB CARDS OCTOBER 1970 FREE SHIPPING For fastest service, send faulty tuner with tubes, shields and all broken parts t0: LABELS HOME OFFICE -Box EAST- Box SOUTHEAST- 4451 SOUTHWEST- Box WEST- Box 272-Bloomington, Ind. 47401 334-W. Springfield, Ma. 01089 N.W. 37th Ave., Miami, Fla. 33142 7332- Longview, Tex. 75601 1431-Turlock, Calif. 95380 Tel. Tel. Tel. Tel. Tel. 812/824-93M 413/734 -2737 305/633 -0002 214/753-4334 209/632.2928 Circle 12 on reader service card 17 www.americanradiohistory.com NTS outs a whole new world at your tinúu'tivs. NTS home training can put a whole new way of life in the palm of your hand. A new, exciting job, a much bigger income is now easily within your reach. NTS training is something special. We provide all the kits you need for the most effective training. National Technical Schools sends kits with every course, and teaches you to build and test a 18 - wide range of professional equip- ment the same kind of equipment you'll actually use on the job. -That's the NTS "Project Method" training that's practical and in- depth. You learn everything from fundamentals to the latest innovations. From beginning to end, NTS makes it fascinating and fun to learn this way. And all you need is a little spare time and an interest in electronics. Each year, men are moving into important new jobs, or their own businesses, straight out of NTS electronics training. NTS is what's happening to men everywhere. Check the coupon. Take hold of the career you want most. Do it now. No obligation. No salesman will call. RADIO-ELECTRONICS www.americanradiohistory.com We aacN your electronics course with kits to make your traioin fast. You'll min every minute of it. NTS COLOR TV SERVICING ro .fir. COLOR TV 295 SO. IN. PICTURE`' NTS training provides an easy way to become a professional home entertainment service technician. You receive a big screen Color TV with many unique features. The unit even includes self servicing equipment that permits you to make all normal test operations. No additional test equipment is needed for adjusting your set. In addition you get an AM -SW radio, Solid -State radio, Field- Effect Transistor Volt -Ohm- meter, and Electronic Tube Tester. You learn about Electronic principles and trouble shooting, hi -fi, multiplex systems, stereo, and color TV servicing. NTS COMPUTER ELECTRONICS This is the future. And it's happening now. The number of computers will increase many times in the next few years. NTS offers a solid grounding in com- puter operation, wiring, data pro- cessing and programming. One of the 10 important kits included is our exclusive Compu -Trainer®. It's a fully - - operational computer logic trainer loaded with integrated circuits the first ever offered in home study. It introduces you quickly to how, w..h. aftr,omwhtheneorayndto why of computers practical servicing techniques. This unit is capable of performing 50,000 operations per second. NTS ELECTRONICS COMMUNICATIONS Choose from two exciting courses to get into the big -paying fields of transmitting and receiving equipment: (1) The FCC License Course. (2) The Master Course in Electronic Communications (more comprehensive, with Citizens' Band Two -WayRadio). Either Communications program qualifies you for your FCC - First Class Commercial Radio-Tele- phone License NTS assures you will pass this FCC exam within six months after successfully completing your course or your tuition is - refunded. Kits include an Amateur- Phone 6 Meter VHF Transceiver NTS exclusive, 6 transistor Solid State Radio, Volt-Ohmmeter (fully transistorized). - ,... NTS AUTOMATION/ INDUSTRIAL ELECTRONICS Let NTS put you into the age of electronic controls. Systems Automation is rapidly becoming the emphasis of modern industry. Your NTS training in automation electronics includes equipment like a 5" wide band Oscilloscope. You also get the new NTS -a Electronics Lab. It's an exclusive NTS experimental laboratory complete workshop that simplifies learning about solid- state, miniature and integrated circuits. 5" Oscilloscope CLASSROOM TRAINING AT LOS ANGELES You can take classroom training at Los Angeles in sunny Southern California. NTS occupies a city block with over a million dollars in facilities devoted exclusively to technical training. Check box in coupon. NATIONAL SCHOOLS WORLDWIDE TRAINING SINCE 1905 4000 South Figueroa Street Los Angeles, Calif. 90037, U.S.A. Exclusive new Compu -Trainer rIf card is missing check coupon and mail for free color catalog and sample lesson. Now. National Technical Schools 4000 S. Figueroa St., Los Angeles, Calif. 90037 Please rush Free Color Catalog and Sample course Lesson, checked plus below. information on No obligation. No salesman will call. L Y/ V l. I V ö C K I U 5 Watt AM Transmitter/ Receiver Master Course in Color TV Servicing Color TV Servicing Master Course in TV & Radio Servicing Practical TV & Radio Servicing Master Course in Electronic Comm. FCC License Course Master Course in Electronics Tech. Industrial and Automation Electronics Computer Electronics Basic Electronics APPROVED FOR VETERANS Accredited Member: National Association of Trade and Technical Schools; National Home Study Council. Name Age Address City State Zip Check if interested in Veteran Training under new G.I. Bill Check if interested only in Classroom Training at Los Angeles Dept. 206 -100 J 21 www.americanradiohistory.com CORRESPONDENCE (continued from page 16) PRINTED- CIRCUIT PATTERNS I quite enjoy your magazine, especially the many fine construction articles you have presented in the past. However, I am experiencing difficulty in having negatives of the printed -circuit layouts reproduced, due to copyright laws which commercial print shops must abide by. I would appreciate your sending me a release to photocopy the printed circuit layouts for photo-etching my boards. HOWARD F. GARRISON Englewood, Colo. The photocopy shop is right. For them to go ahead and duplicate without permission does violate the copyright laws. However, it is our intent, when we present a printed circuit layout, to have our readers use the pattern to make hoards for their own personal use. Therefore, we do authorize readers to use these patterns and make copies of them for their convenience in the construction of the particular article described; provided this is not for manufacture and is for their personal use.-Editor WHY NOT TUBES? I want to congratulate your magazine for the challenging projects that are published in its pages. But I notice that most of the electronics magazines publish only construction articles based on solid -state components. I agree that this type of project has its advantages over the tube based ones, but I feel that tubes are not yet out and that the reader should have a chance to acquire some practical background on the operation of tube equipment. Also, many readers have various amounts of tubes on hand and the surplus market is loaded with inexpensive ones. So how about some articles with vacuum tubes? UBALDO ORGNERO Calgary, Canada We agree that tubes are not dead, but in many instances there is little excuse for using them. The transistor is often easier and less expensive to use, and always smaller. When you use tubes you have a much more complex power supply associated with the circuitry too. We will present articles using tubes whenever the use of tubes gives the reader a tangible advantage; perhaps in high -frequency applications or extremely high-power circuits. otherwise we will continue to present projects based on solid -state com- ponents.- Editor KWIK -FIX MIXUP Two errors appeared in the June 1970 issue that should be of interest to all readers. In the Kwik-Fix article, page 44. second column; the first paragraph reads "Both horizontal and vertical blanking are applied to the emitter of Q1 by R6. R5 and C2 shape the hori- zontal pulse. These positive -going pul- ses bias the transistor completely off for their duration. That makes high - amplitude negative -going pulses in the collector." This is erroneous; there is no in- version when a signal is applied to the emitter. Applying a positive-going pulse to the emitter is the same as ap- plying a negative -going pulse to the base. The second sentence in the sec- ond column of the same article on page 44 reads "L2 and L4 are a matched load for the load line." Ac- tually L4 is the peaking coil of V2. B. J. BROWN Trion, Ga. R-E IN THIS ISSUE Stereo system not delivering top performance. Better take a look at the article starting on page 40. Peter Sutheim tells how to get better sound from your stereo system. 99.99% reliable - Every now and then, one of our tubes fizzles and somehow it's the one you install. Even we don't know how you happen to receive that particular tube. But we do know that it doesn't happen more than once in thousands of times. Raytheon receiving tubes -including Raytheon Tubes for Imported Sets-have to be extra reliable. Because, Raytheon is the leading independent supplier of receiving tubes to ;independent servicemen. We don't have competing service trucks or retail outlets. So, we depend on you just as much as you depend on us. RAYTHEON Circle 13 on reader service card 22 RADIO- ELECTRONICS www.americanradiohistory.com finally! Fl visually perfect fini wave! OCTOBER 1970 -it The sine wave above was generated by Shure's design computer like the sine ... Super Track wave that Cartridge was generated by the Shure in the Hirsch -Houck testing V -15 Type 11 laboratories first cartridge we have tested to have done so," according to their looks Improved "the published SHViRE yh3w"rote0ereupaarceovcmytrkht.a/iembsbTaepifshlcurisitelsyls1bs,H0pace0enihdr0drsa,fcsemHhcazoptn-niHdobsoanitnhwnu.e"edcekwCoSwafoRhevotuerhekerpeeowSrpFeBtalaersroiioaerntcsgsheheet6dinhlr0d.eesrtAa1em0tnse1pdtd- treewdscuetor'rlrilndegcbaoetrthd3ep/4aletpagl1sraaeygmdinr,agmtaon.odfsTehtthnheedey Inc., 222 Hartrey Ave., Evanston, Ill. 60204. AN co( ir 14 nn rcurl( r.1errice care/ 23 www.americanradiohistory.com ... In the Shop With Jack By JACK DARR SERVICE EDITOR another great new idea reversible rfichei for hang es Xcelite "99" tools 0 C 0 0 0© 0 0 These two unique plastic (UL) handles extend the usefulness of all Xcelite Series "99" tools, make welcome additions to any "99" set. Both regular (99-1R) and Tee (99-4R) types accept more than 60 individually available nutdriver, screwdriver, and special purpose snap-in blades to speed and simplify assembly and service work. Fully enclosed ratchet mechanism is built to highest socket wrench quality standards. Recessed reversing shift operates at the flick of a thumb. Patented spring chuck holds blades firmly. nationwide availability through local distributors REQUEST BULLETIN N670 Made in U.S.A. Cirjrria XCELITE, INC., 10 Bank St., Orchard Park, N. Y. 14127 In Canada contact Charles W. Pointon, Ltd. Circle 15 on reader service card 24 Ripple and Noise; Unfiltered Rig "Ripple" is what you have left over after you get through filtering the dc power supply. Like all leftovers, it can cause trouble. Turkey hash for 6 days in a row is monotonous. It's not the actual -of 60- or 120 -Hz ripple itself which causes the trouble course you can get a faint hum -bar or two in the picture, but this isn't the worst of it. The presence of 60 -Hz ripple in- dicates far more serious trouble. When this is above normal limits, your dc power supply filtering, or more accu- rately, decoupling, is a long way from be- ing good enough. In all electronic circuits, one thing is common to all stages -the dc power supply. With the great number of different spikes, pulses, signals of all fre- quencies, and so on, that you have, it is absolutely imperative that you get rid of them after you've used them! If any of them is allowed to get into another stage, you'll really find some weird and unusual troubles. This is caused by feedback. Even if it is only from the output of a stage to its input, this can cause oscillation or in- stability. If they happen to get back in the right phase, it can cause degenera- tion and "mysteriously" reduce the gain of a stage. If the feedback signal comes from a stage with different signals, we -a get some real howlers. Example horizontal -frequency sawtooth or spike signal getting into the video amplifier stage. This causes hori- zontal shading of the raster-one side is darker than the other. Vertical -fre- quency feedback causes shading from top to bottom. If this is strong enough, you get the odd symptom of the picture "going out from top to bottom" as the brightness is turned off, as if you were pulling a shade down over it. The key clue in such cases is the nature of the effect. Side -to-side shading is coming from the horizontal circuits; top-tó-bot- tom shading from the vertical. In either case, the basic cause is the same -feedback. Feedback happens be- cause the filtering is not good enough. In the "source- stage" this signal, after we've used it to sweep the screen, has to go somewhere. It's supposed to go back to the (common) power-supply, and from there straight to ground. This signal is "ac." It goes to ground because the normal impedance of the dc power supply is very low. For example, a 50 -1.LF capacitor has 63.7 ohms reactance at 50 Hz. At 5000 Hz, only 0.637 ohm. At 15,750 Hz, this gets down to about 0.2 ohm or so. (This is why you will see a greater 60 -Hz ripple than the other frequencies-the lower the frequency the greater the reactance of a capacitor Xc = 1 In practical 2a-fC circuits, you'll find several capacitors to- taling 200- to 300-µF or more, and a total impedance of practically zero ohms. We've got to keep this impedance very low to prevent feedback at any fre- quency. The used signals must be "drained off" to keep them out of mis- chief. Think of this in terms of plain old resistance. If we had a 100 mA signal flowing through a 100 ohm resistance, we'd develop a 10-volt ripple. This will actually cause the plate voltage (or collec- tor voltage) of stages fed from this line to vary 10 volts. You can see what kind of trouble that would cause! The easiest way of finding this kind of trouble is with your scope. Just touch the direct probe to the hot terminals of all electrolytic capacitors anywhere near the circuit which is showing signs of trouble. A good trick is to set the scope up for a certain deflection at 1.0 volt p- p. Any ripple greater than this is very apt to cause trouble. Don't confine your efforts to 60 -Hz ripple alone! Anything you see on there, except a nice straight "dc line" means trouble! In tube circuits, you'll find 6 to 8 volts of ripple (60 -Hz) at the rectifier output. However, at the filter output this had better be down to about 1.0 volt p -p maximum. One volt of ripple in a 300- to 400 -volt circuit won't be too bad sim- ply because of the very small per- centage. In transistor power supplies, with their far lower voltages, a 1.0 -volt ripple means difficulties; percentage again. Solid-state power supply circuits use very large filter capacitors. You'll find several thousand microfarads of fil- ter capacitance. The quickest check in a tube circuit is to bridge a good capacitor across the suspected unit. Look for the ripple to disappear. If it does, replace the capacitor. DO NOT (Repeat: DO NOT) bridge large filter capacitors across tran- sistor power supply circuits. Turn it off, hook up the new unit, then turn it back on. The charging surge of a 2000-SF ca- pacitor is fearsome and can easily blow a fuse or pop a transistor. Sometimes the ripple won't go away, but will merely drop a little when a new capacitor is bridged across the old one. If this happens, the old capacitor probably has a high power factor (loss of filtering efficiency) and it will have to be taken completely out of the circuit and replaced by a good one to clear up the trouble. R -E RADIO -ELECTRONICS www.americanradiohistory.com don't miss this opportunity If You Have What It Takes to Qualify for Training in Electronics We'll Not Only Train You... We'll Help You Finance Training and Help Place You In the Job You Want! Just a few short years ago, who could have imagined electronic marvels like the micro -miniaturized printed circuit, no larger than the head of powered heartbeat regulators ... a pin ... battery computers that - make split- second calculations it would take the human brain years to duplicate! This is the amazing world of technology. The demand for trained Electronics Specialists and Draftsmen is increasing every year! These are well paid, prestige positions with practically unlimited opportunities for advancement. In 12 months or less, United Technical Institute can prepare you to take your place in this dynamic, expanding field. You can - study right at home, in your spare time and at your own pace or attend a UTI resident school near you. Because UTI is an eligible institution under the Federally Insured Student Loan Program, you may attend the Institute on a government-guaranteed educational loan. And after you finish your training, we can help you find your first position! Accredited Member of National Technical Schools. Approved for Association of Trade Veteran Training. and Get the facts now! Just clip the coupon and send today for a FREE, fact-filled book describing the exciting opportunities in electronics, and how you can qualify for them. We'll rush your book by return mail so you can read it and - decide for yourself. No obligation, of course. But don't delay clip the coupon for your free book today! United Technical Institute .4501, fJ- J division of Career Academy 125 W. Wells St. Milwaukee, Wis. 53203 Dept. 07N215205 Please rush me your free 28 page with all the booklet details on your Electronics course I I Name Address (Please print) City State Phone Lam interested in: El Classroom Study El Home Study Age Zip El Facts on GI Bill j I I Circle 16 on reader service card OCTOBER 1970 25 www.americanradiohistory.com SPECTRUM PRODUCTS PRESENTS HIGH QUALITY POWER AMPLIFIERS AT MANUFACTURERS PRICES > EQUIPMENT REPORT Heathkit 1G-57 Post-Marker Sweep Generator For manufacturer's literature, circle No. 21 on Reader Service Card. {! . ;C .4 ,.._E «.xt 2, ONE FET AND 7 SILICON TRANSISTORS. - POWER OUTPUT. 25 watts RMS at 8 ohm load. (35 watts IHF music power) FREQUENCY RESPONSE. 1DB from 10Hz to 50,- 000Hz at full RMS output. DISTORTION. Less than one (1) percent. THREE INPUT CHANNELS. One megohm FET high im- pedance input, and two (2) low impedance inputs. INPUT SENSITIVITY. High impedance .5 volt for full RMS output. Low impedance .25 volt for full RMS output. Low impedance 1.5 volt for full RMS output. TRANSISTORIZED TEMPERATURE SENSOR. Holds idle current at a constant 10 ma. preventing thermal damage. DC OPERATING VOLTAGE. 45 volts. DC OPERATING CURRENT. 10 ma. idle, 1 ampere at full IHF output.. OVERALL DIMENSIONS, 4x4x2 inches. PRICE. $16.50 SPECTRUM PRODUCTS PRESENTS THE NEW SELECTRA -MATIC POWER AMPLIFIER ONE FET AND 7 SILICON TRANSISTORS. SELECTRA- MATIC. Automatically lets you select any power from RMS at 8 ohm load. (22 watts music power] FREQUENCY RESPONSE. 3DB from 10Hz to 50,000Hz at full RMS output. DISTORTION. Less than 1 percent. THREE INPUT CHANNELS. One megohm impedance input. Two low- impedance FET high inputs. INPUT SENSITIVITY. (35 ance .25 volt for full impedance .5 volt for volt RMS full supply) High impedoutput. Input (1) Low RMS output. Input (2) Low impedance .05 volt for full RMS output. TRANSISTORIZED CURRENT CONTROL. Automatically holds distortion at a minimum. TRANSISTORIZED TEMPERATURE SENSOR. current at a constant 20 ma. thus Holds idle preventing thermal damage. DC OPERATING VOLTAGE. Anywhere from 12 to 35 volts. DC OPERATING CURRENT. 20 ma. idle. 750 ma. at full IHF output. OVERALL PRICE.$ 6 50, twoN(2) for >/s inches. $31 00 SATISFACTION GUARANTEED SPECTRUM PRODUCTS P.O. BOX 2562 CULVER CITY, CALIFORNIA 90230 Circle 17 on reader service card 26 THE MORE THINGS A SINGLE TEST IN- strument can do, the more valuable it is in the service shop. The Heathkit IG-57 TV Post-Marker Sweep Generator certainly meets this evaluation. With this ver- satile test instrument, you can use sweep-alignment techniques on any stan- dard piece of electronic equipment "with the greatest of ease" and accuracy. Many technicians have hesitated to use sweep alignment in the past, simply because it was such a hassle getting ev- erything hooked up; also because of a nagging doubt that it wasn't accurate! Previous methods of putting markers on the sweep curve caused several troubles, the worst of which was actual distortion of the curve by the markers. In the end, we actually did not know whether we had helped alignment or made it worse. With the system used in the IG-57, this doubt is gone. It uses the "postmarker" circuit; this is the only way in which frequency markers can be added to sweep- response curves without distortion of or interference with the actual frequency response of the unit being aligned. The markers are put on the curve after it has gone through the tuner circuits. A special "marker- amplifier" and mixer circuit is used. The marker frequencies cannot affect the response of the tuned circuits. Amplitude of the curve and the markers can be controlled individually. Above all, the whole thing is simple. Two cables connect to the TV set, sweep input and output, and two to the scope, vertical and horizontal inputs. Turn it on and away you go. To further reduce clutter on the bench, the IG-57 even has two dc bias supplies on its front panel; many alignment instructions specify a fixed bias, especially in color TV i.f.'s. No separate bias box is needed. The dc voltage goes to 15 volts, and the polarity can be reversed, if necessary, for use with transistor forward- bias agc, etc. The list of specifications for the íG- 57 is fascinating. The instrument provides three sweep ranges: Low, 2.5 to 5.5 MHz, for color bandpass and sound i.f. alignment. The 10.7 -MHz i.f. of FM tuners can be swept by the 2nd harmonics on Low. Next, IF for TV i.f. alignment covers 38 to 49 MHz, on fundamentals. Finally, the RF sweep goes from 64 to 72 MHz (channel 4) and a high band (192-198 MHz, channel 10) on the harmonic. All these have a minimum signal output of 0.5 volt (500,000 µV ) which is, as one of my colleagues used to say, "enough to blow a signal through an inch pine plank!" However, as in all sweep alignment, it is the markers which are the most im- portant. Marker accuracy is the key to the usefulness of any sweep generator, and the thing which has caused us the most trouble in the past. The IG-57 meets this requirement by using crystal oscillators. There are 16 of these, each individually controlled by switches on the top of the front panel. One very important part of the i.f. sweep alignment procedure is now much simpler-trap alignment. This is vital in color TV alignment. A misplaced trap can cause color suckouts and a multi- tude of other problems. (For a test, try running the 41.25 -MHz trap up on the side of the curve till it gets the color carrier, and you'll find out!) With the crystal markers, the three most impor- tant traps- 39.75, 41.25 and 45.75 MHz, can be tuned right on the nose. For additional help in this, as well as in sound i.f., sound detector, stereo FM and aft alignment, a 400 -Hz signal can be modulated onto the marker sig- nal. The trap is simply tuned until audio modulation is at its lowest point, and there you are-the trap is now at its maximum attenuation. Or a sound detec- tor is aligned for maximum AM rejec- tion. which is the "right place." Special connecting cables and probes are used. These have tiny clips for connecting into the circuits. An rf probe is used for i.f. and rf alignment, and a demodulator probe can be used at intermediate points through the TV i.f. (specified in some manufacturer's align- ment instructions, for link and trap alignment). Incidentally, these probes are light and small. Frequency modulation (sweep) is done with an all-electronic circuit using a controllable inductor. No more me- chanical sweeps, with hums and buzzes. Tiny toroidal cores coupled to the in- ductor control the amount of frequency deviation (sweep width) and the center- ing. These two things are controlled by a concentric dual-knob on the panel, for one-hand operation. Incidentally, the "curve height" ("Trace Height") and marker pip amplitude ( "Marker Height ") are also a concentric dual con- trol. This makes adjustment of the curve height on the scope and the marker heights on the curve very easy. A separate seven -step attenuator is pro- vided for regulating the output signal voltage. This has 1.0-dB, 3.0-dB, 6.0-dB. two 10-dB and two 20-dB positions. Any or all of these can be used simulta- neously. With this accurate attenuator, the scope can be calibrated in dB; this makes alignment with markers set "so many dB down" from a given point very simple. The IG-57 is available from Heath as a ready-made instrument or in kit form. R -E RADIO-ELECTRONICS www.americanradiohistory.com Newest SAMS Books Hi -Fi Stereo Servicing Guide by ROBERT G. MIDDLETON. A complete guide to effective hi -fi and stereo servicing. Provides the basis for a full understanding of hi-fi tuner and amplifier circuitry and procedures for servicing this type of equipment. The proper use of audio test and measurement equipment and the basic principles of acoustics are also given. Covers all hi -fi components (except record players and tape recorders). Order 20785, only $3.95 ABC's of Avionics dbeyrsLtEanXdPinAgRRoIfSHav. ioPnroicvsid-tehs ea basic unelectronic equipment used to insure the safety of crew and passengers. The type of equip- ment and the techniques employed in private aircraft operations are featured. Discusses requirements for basic com- munications, navigation aids, instru- ment flight aids, weather guidance, and flight control safety devices Order 20764, only $3.50 Mobile -Radio Systems Planning by LEO G. SANDS. Here is practical, basic information about various types of mobile-radio systems, how they work, their capabilities and limitations, system requirements, licenses, channels, band and frequency selection, transmitter- receiver selection, antenna systems, and accessories. Includes an invaluable system-requirements form for planning a mobile-radio system Order 20780, only $4.50 Transistor-TV Servicing Made Easy by JACk DARR. This practical guide will help you become skilled in the special techniques of transistor-TV servicing. Ctroavnesrissttooroslsaanndd terqaunispimsteonrt-sreerqvuiicriendg; techniques; power supplies; horizontal and vertical sweep circuits; video i -f and output circuits; agc arator problems; tuners; and sync -sepaudio circuits; and selecting replacement transistors. Order 20776, only $4.95 Security Electronics botrypoenJrOiacHtdiNnegvEi.cpeCrsUinaNcnNidIpNslGeyHsstAeoMmf . smEuoxsdpeedlranitnoseplterhoce-- vide security against crime. Describes ditineottnreucdstiieoovnniceaoslf.ahrImindcdsleuandnedms eicnthatarluposteiborjsenc-otdsn,ettaehnce-- nouncement of detected intrusions, bug- ging, debugging, and speech-scrambling systems, and future developments. Order 20767, only $4.50 How to Hear, Police, Fire, and Aircraft Radio by II, LEN BUCKWALTER. After World War police, fire, and aircraft radio moved to the less crowded vhf bands, and the "police band ", which was found in many older radios, was silenced. Few listeners had vhf braencde,ivbeerscacuaspeatbhleeyowf ecroevreerliantgivethlye estitxvapeteelynsciilvrocew.u-ictWroysi,tthamtwohniediteoardvinvagerinetetyqoufoipfsmoreleilnda-t- is available. This book is a guide to the selection and use of vhf radio. Order 20781, only $3.50 HI -FI STEREO 101 Questions and Answers About Transistor Circuits bcsmciouysemitntoLmcrcEloaocOtninurflcGryieug. ,iautSsrrbAkayiteNa.idsoDEinnSqx.sgup,,eAltaishnntiienspowsunthtetsrrraseaanenbstdobhiusaetsotoiuctrmrtapnconiours---tt aimndpeodtahnecresb,asciucrrceonntsiadnerdatvioonlsta. gCe ogvaeinrs, power supplies rf circuits, and and circuits; oscillators. of circuits; Order 20782, only $3.50 lIII /N, rrryuin/xui,rrl.utr' 14 1%1. antn.J.inlru/hYi'le. 1 -2 -3 -4 Servicing Automobile Stereo bpmtcroylieicvetaFehsOlroRtdethEhqeSteuoTiipneHbmlg.eoeeBctnnhtEritLo.omTnu.IisetcTch"thah1aines-ndn2ibc-o3apmol-rk4eoa"ccnfheidrreasedntepsilcaaetpacior-l- tpmFhrieuninlatmclilpiyepl,telhextohsdaeontbfdooaaotuaukpttooesmhscotoawebrrsteirlohiedosgwysestettseorymesoastep,. mpflmsy. Order 20737, only $3.95 Aviation Electronics, 2nd Edition nsaamtmstbbreiyvuioyagmceusitonniaatonKaskess,tminEmpiucuosIfooraaT,ssonipntten,HriiadedgceoanreWalnnaeiedridns.tcqdrsiictBureoarraaeOrnionvapenncgSni,flmtddEatiaiinc.taoteiowseeinnoTnnweddene-thrs,fnaqstiidtermotsunheoeurmidsepvxpdam,erirpmniacranleyipseracertna.,isaeitnlnditnontcds-aa.tgaailsnrseanltC,,dht,ncahoetAcdeneavsoicTcnydemnheosderCg-s---f-- Order 20743, only $9.95 Questions & Answers on Short -Wave Listening bgiQtqicasnieruuyougeieitvnedrneHcsaaeactdo.lnfiit;fnoesooCssnsmarH,htstdrnhiAoauetdeanRtrdcentdLtid-hedEnbw;dosStyeweaarharvnWvoesnesishswOcdwhtoeObioensroDsrrr;tgohpts-Rh-weaoUwwocrdraFaowtoacvF-tvvr.aewelesesddharAt.rvirooeneeircfncghtelte-e,iiiewisvslvrtpfeaneerrfrvneaeruses---.-l Order 20783, only $3.50 OCTOBER 1970 North American Radio -TV Station Guide, 6th Edition 1 -2 -3 -4 Servicing Transistor Color TV jtbMsttaohohtyebedriespetcFtthmbhoa.OopoieleloRdroetorr"khEdic,ogSeTiTdhstesVhsxteafpHtwoahl.frarsauaeniyBmntqadEuacthpioniaLoelcvmdeTlknpe,.ersltoeonhtTfrdgtedoha,hiouceleosfaabowtlslh,lo"eylef1ostsohwtwt-rseo2aeaaeponrydp--vt3s.pbiiibncly-Isyy4gne-- and easy repairs. bTiaaoSiauccsntyspeVoaiedenpl,wfVrgacusaaelAratnloltaaalNlidcoltnt-aEeainlmgtosetehl,i,ntiAoettsoash.entfrvioWmr,JniasaOsng,ierefNmlestrsaahEettbatanheqSeIklrd.auenmreUa.tedLtpntn.iehaSeiogclsris.eryeset,.avsdgrCIaiisnua(bblaoilcyiyoolndrlnuueaogrctddafesthfeahdottataos,eighnotreiMomnsaopatepanoeaenlhixss)rrrd-,t,-t-. Order 20777, only $4.95 Order 20779, only $2.95 r - - - - - - HOWARD W. SAMS & CO., INC.- Order from your Electronic Parts Distributor, or mail to Howard 4300 W. 62nd St., W. Sams & Co., Inc., Dept. Indianapolis, Ind. 46268 RE -100 Send books checked at right enclosed Send FREE 1970 Sams Book Catalog 20785 20764 20780 20777 20767 20781 Name PLEASE PRINT Address L City State lip Circle 18 on reader service card 20776 20743 20783 20782 20737 20779 J 27 www.americanradiohistory.com www.americanradiohistory.com A Government FCC License can help you bring home up to $10,000, $12,000, and more a year. Read how you can prepare for the license exam at home in your spare time-with a passing grade assured or your money back. IF YOU'RE OUT TO BAG A BETTER JOB in Electronics, you'd better have a Government FCC License. For you'll need it to track down the choicest, best paying jobs that this booming field has to offer. Right now there are 80,000 new openings every year for electronics specialists-jobs paying up to $5, $6, even $7 an hour... $200, $225, $250, a week ... $10,000, $12,000, and up a year! You don't need a college education to make this kind of money in Electronics, or even a high school diploma. But you do need knowledge, knowledge of electronics fundamentals. And there is only one nationally accepted method of measuring this knowl- edge ... the licensing program of the FCC (Federal Communications Commission). Why a license is important An FCC License is a legal requirement if you want - to become a Broadcast Engineer, or get into serv- icing any other kind of transmitting equipment two-way mobile radios, microwave relay links, radar, etc. And even when it's not legally required, a li- cense proves to the world that you understand the principles involved in any electronic device. Thus, an FCC "ticket" can open the doors to thousands of exciting, high-paying jobs in communications, radio and broadcasting, the aerospace program, industrial automation, and many other areas. So why doesn't everyone who wants a good job in Electronics get an FCC License and start cleaning up? The answer: it's not that simple. The government's licensing exam is tough. In fact, an average of two out of every three men who take the FCC exam fail. There is one way, however, of being pretty certain that you will pass the FCC exam. And that is to take one of the FCC home study courses offered by Cleveland Institute of Electronics. CIE courses are so effective that better than 9 out of 10 CIE graduates who take the exam pass it. That's why we can back our courses with this iron- clad Warranty: Upon completing one of our FCC courses, get your you must be license -or able to pass the you'll get your FCC exam and money back! They got their licenses and went on to better jobs The value of CIE training has been demonstrated time and again by the achievements of our thousands of successful students and graduates. Ed Dulaney, Scottsbluff, Nebraska, for example, passed his 1st Class FCC License exam soon after completing his CIE training ... and today is the proud owner of his own mobile radio sales and serv- ice business. "Now I manufacture my own two-way equipment," he writes, "with dealers who sell it in seven different states, and have seven full-time em- ployees on my payroll." Daniel J. Smithwick started his CIE training while in the service, and passed his 2nd Class exam soon after his discharge. Four months later, he reports, "I was promoted to manager of Bell Telephone at La Moure, N.D. This was a very fast promotion and a great deal of the credit goes to CIE." Eugene Frost, Columbus, Ohio, was stuck in low paying TV repair work before enrolling with CIE and earning his FCC License. Today, he's an inspector of major electronics systems for North American Aviation. "I'm working 8 hours a week less," says Mr. Frost, "and earning $228 a month more." Send for FREE book If you'd like to succeed like these men, send for our FREE 24 -page book "How To Get A Commercial FCC License." It ... requirements tells you all about for getting one ... the FCC types of License licenses available ... how the exams are organized and what kinds of questions are asked ...where and when the exams are held, and more. With it you will also receive a second FREE book, "How To Succeed In Electronics," To get both books without cost or obligation, just mail the attached postpaid card. Or, if the card is missing, just mail the coupon below. ENROLL UNDER NEW G.I. BILL. All CIE courses are available under the new G.I. Bill. If you served on active duty since Jan. 31, 1955, or are in service now, check box on reply card for complete details. CoIEfCElelveeclatnrdonInicsstitute 1776 E.17th St., Cleveland, Ohio 44114 Accredited Member National Home Study Council rA Leader in Electronics Training ... Since 1934 ll Cleveland Institute of Electronics 1776 East 17th Street, Cleveland, Ohio 44114 Please send me without cost or obligation: tttohrodeYnmaiyoc.u,sr"an4d4de-sphcaorgiwbeinybgoouolrokbc"ooHuporpswoerstutocnaitnSieuspcrcieenpeadErleeIcnmtroeEnlifecocs-r Your book on "How To Get A Commercial FCC License." I am especially interested in: E lectronics Technology B roadcast Engineering First Class FCC License Electronic Communications Industrial Electronics Electronics Engineering 2 NEW CIE CAREER COURSES Name 1. BROADCAST (Radio and TV) ENGINEERING... nMouwltipinlecxlu, dCesoloVr iTderaonsSmyisttteemr sO, pMeraotnioitnorsa,ndFCMATSVt.ereo 2. ELECTRONICS state and transient ENGINEERING. .. covers network theory, solid state steady physics and circuitry, pulse techniques, computer logic and mfoarthmeemnatailcrseadthyrowuogrhkincgalicnulEulse.ctAroncicosl.lege-level course Address !PLEASE PRINT) City State Zip L Check here for G.I. Bill information OCTOBER 1970 Circle 19 on reader service card Age__ RE -83 - J 31 www.americanradiohistory.com ving Tubes Picture Tubes ECG Semiconductors The long awaited and newly revised Sylvania Technical Manual is out. Complete and unexpurgated. The fantasy of every Independent Service Technician. Written anonymously by an agile team of Sylvania engineers. 32,000 components described in breathtaking detail. Including thousands of unretouched diagrams and illustrations. Discover "Electrifying" the unspeakable thrill of new color TV Tubes, listed as never before. The ecstasy of 28,000 ECG Semi- conductors. From exotic Deflection Oscillators to a lurid ac- count of Transistors and Rectifiers. This book has what you want. Components for the man who knows what to do with them. The 14th Edition of the Sylvania Technical Man- ual is not available in any bookstore. Your Sylvania Distributor is discreet. Speak to him. SYLVAN IA GENERAL TELEPHONE & ELECTRONICS 32 RADIO -ELECTRONICS www.americanradiohistory.com 11 is all to recor rou rb econ not ill w ty pr rec corm ad i ratio ring ad, pes ng t effe 11 wa sles istudi quad iv .:. ; . ` ove over sior& to .1 t ,y _-L-: stv> f11' í , he good r- o :.. inns . ruiu Q. able; y.. a . New 4-cimiinci stereo techniques by WALTER G. SALM xr!r . iril! Py Z.R:i,T` , s 3 - . rrrat y:.:a: ü I rrQ.H..L>F.- g:í.T,..atWiasn°itti,,. [ . 4- channel stereo is here to stay. Here's the latest on what's happening in this new race for solid sound that surrounds the listener l ` r yf . . - . bled. 1 mor ective short recor eight - es in can b y time e lots eo rec Vi reacItEre esy-at--least-on -store rfi -se with i.: - . Aam Tart!is..Y ; version heads-for k are exixerrsive mplifiers like r.r,- 1. .ri-r.=i"y:4`- .ÿy-: re ma y rec rc can -fillin very ith orc he co Scheme "ultimate ile he en, so tional sound t-r all, i rig from OCTOBER 1970 n niproveni www.americanradiohistory.com just as effective and solve all these problems? And so it goes. Here's what's happening now. Tape equipment is in the forefront, as it was in 1956. Companies now producing quad playback-capable equipment include: Crown International, Teac, H. H. Scott, 3M and Telex /Viking. Ampex has produced quad equipment for professional use, machines that will handle both 1/2inch and 1/4 -inch tape, but an Ampex consumer quad unit may not be far away. At the CES show in New York Ampex showed a four-channel cassette player. Kenrich Purchasing, an importer of Japanese cassette recorders, plans to market an inexpensive quad conversion kit for cassette surround sound. The basic unit looks little different from any living -room version of a cartridge player. It has two speakers built into its cabinet, but also has two outboard speakers at the rear of the listening room. And there in lies the difference. The same unit can be used with four outboard speakers, as is another unit that has no built -in speak- ers. The cartridge machine is com- patible with conventional 2- channel stereo tapes. All it takes is a flip of a front -panel switch to go from quad to old- fashioned stereo. The track arrangement is 1 -3 -5-7 for sequence A with 1 as left front, ,.3 left rear, 5 right 4-track in a cartridge Possibly the easiest single format to work with for home entertainment use is the 8- track, continuous -loop cartridge. This cartridge has sufficient tape width to accommodate two four- channel programs with interleaved tracks, making playback heads easier and cheaper to build. Bearing this out TYPICAL 4- CHANNEL STEREO AMPLIFIER. This one is the H. H. Scott model 499. Several other manufacturers have announced similar gear. front and 7 right rear. At the end of have been twin announcements by sequence A, the head shifts down and Motorola and RCA. Motorola said it plays tracks 2-4-6-8. Program time is had a four-channel stereo 8 -track tape halved by the quad format so a player for the car and would be in- double-length tape becomes instead troducing it later this year. No men- standard album -length. Presumably tion was made of where the tapes were the tapes will be priced somewhat to come from. higher than standard 2- channel car- At virtually the same time, RCA tridges and because of the use of four unveiled a living-room quad system tracks, will have half the playing time. also based on the 8-track cartridge. This one was more realistic, since RCA can make its own quad tape car- - Tapes should be available now. One of the few amplifiers on the scene so far is the Scott "Quadrant" tridges very easily and demonstrated a 35- watt-per-channel unit with an imsome new ones in the prototype dem- pressive number of front-panel con- onstration. trols and a staggering price tag of K(;H t5TK LORC H ESTRIi ORCHESTRH o TRACK O 2 TRACK O 3 TRACK O 4 TRACK ORO OLO L R WGBH WCRB O W NYC L R Q WKCR O L R $600.00. Interestingly, the unit has two different stereo headphone jacks-one for the front speaker pair and one for the rear speaker pair. The front -pair jack is used when listening to conventional 2-channel stereo. Eventually, such amplifiers will no doubt have a single headphone jack with choices of various blends for both two -channel monitoring and the most suitable mix for casual listening, and the owner will make his choice. The broadcast situation is far from clear. Even as we go to press, there's every chance that the FCC will grant that all- important experimental broadcast approval. In the meantime, the only quadcasts that have been legally possible have been via two stereo FM stations paired up with rented telephone lines. The listener needs two complete stereo receiver setups to listen to these limited quadcasts. Sound familiar? Other systems are available, but won't be heard by the public until the FCC issues the necessary experimental license. Latest word on the status of single- station broadcast is that no one can seem to make up their minds as to what is desirable and not. It's generally conceded that if a station's going to broadcast quad, then its SCA channel must go. SCA is that special service channel with a 67 -kHz subcarrier that carries background music or other special programs to paying customers. SCA has in fact become the focal point of disputes between proponents of different kinds of quad transmission systems, and often the feuders have other, SCA-bred axes of their own to grind. A basic system suggested by William Halstead ("Mr. Multiplex") RECORDING, BROADCAST AND PLAYBACK techniques are shown on the left as they are now being used. FOUR -CHANNEL TAPE, reel -to -reel is the Telex Quad S -nic Model 230 below. QQ transport is for playback only; QQRM handles both recording and playback. oL FRONT Ro [ OL SOFA FT Ro REAR 34 --1 ORCHESTRA , O O L R K-101 KRON L R O O RADIO- ELECTRONICS www.americanradiohistory.com working with Leonard Feldman, uses two 8- kHz -wide subchannels for the two rear speakers, with subcarrier frequencies at 69 and 89 kHz. This technique has a certain amount of overlap with the alloted SCA channel (59 to 75 kHz), so the SCA capability is automatically eliminated in stations that quadcast. One serious problem here is the fact that any quad decoder for such a system would also be capable of picking up SCA channels, because of this overlap between SCA and the lower of the two quad sub- channels. To avoid any outcries of "SCA piracy," Feldman has installed a tiny reed relay in the quad decoder circuit that automatically mutes the detector's output when a 67 -kHz subcarrier is received. This idea easily wins the Rube Goldberg medal and does nothing to stop the tinkerer who wants to bridge across the relay to get SCA. Another technique, formally pro- posed to the FCC by McMartin Industries and later withdrawn, uses a form of time- division multiplexing (TDM). This technique intermixes the two signals at a 19-kHz rate. Channel bandwidth is held to 8 -kHz per channel and in the playback, sampling is locked to the 19 -kHz stereo pilot signal. This signal enve- lope embraces good old 67-kHz as a center frequency (suppressed) and is amplitude -modulated to prevent any eavesdroppers from illicitly picking up SCA broadcasts which happen to be McMartin's bread and butter. Main problem with the TDM technique is phase distortion. Add just one tiny bit of phase delay because of propagation conditions and the signal separation goes to pieces. Actually, there's little reason not to adapt the Halstead/Feldman sys- tem AM by converting both with suppressed channels to carriers -the same transmission method used for the FM stereo subchannel. This way, quad decoders wouldn't pick up SCA, reed-relays notwithstanding, and broadcast modulation level could be held at reasonable proportions. Some people, both in the FCC and out, are understandably nervous about the proposed additional use of the FM band. Anything above the as- signed 150-kHz bandwidth is dan- gerous, they believe, and might cause co- channel interference. Not so. The actual bandwidth in use would never go above 150-kHz, simply because bandwidth use is a function modu- lation percentage. In the present setup, a station broadcasting mono FM can use 100% modulation which effec- tively eats up that full 150 -kHz. If the station broadcasts FM stereo, it re- duces its main -channel modulation to -R 80%, uses 10% for the 19-kHz pilot and 10% for the L stereo infor- mation on the subchannel. If the sta- tion carries SCA, it reduces the main channel another 10%. This brings us down to 70% main-channel modu- lation. If two quad channels were to be added, they would each probably re- quire 10% modulation. Since SCA can't be carried during a quadcast, there's 10% available right there. Chop off another 10% from the main carrier-leaving 60% and we have our quadcast setup. What would this do to signal-to-noise ratio? Not much. Each 10% reduction in main-channel modu- SYSTEM USED BY DYNACO to add front (F) and back (B) information to left and right channels. SPEAKER ARRANGE- MENT nel. All for turning you must existing 2- channel system into pseudo add are two additional speakers and a 4 -chanspecial matrix adjust thneetawmoprklifie(srhobwanlanbceelocwo)n. trWolhefonr using this minimum arrangement sound in the back speaker when monophonic material is being played. -a lation results in a loss of about 1.5 dB of S/N radio cheap price to pay for so much extra sound. Thus a quadcasting station would have about 1.5 dB poorer S/N ratio on its main channel than would a stereo station carrying SCA. What will happen? What actually happens will probably follow the pattern set in 19561961. Someone will propose a definite system that will be fully compatible with conventional stereo and mono reception. A limited number of decoders will be produced and sold at a premium price to experimenters who will use them to listen to perhaps one or two hours a week of test quadcasts. Other systems will be proposed, in increasing numbers. The closer the FCC comes to making a decision, the more companies will get into the act-each one with a quad transmission system of its own. Ultimately, the system selected as the industry standard will not be one of those that had had experimental quadcast experience, but will be one of convenience, and possibly one that will still permit SCA transmission! But perhaps the Commission will recognize the fact that SCA is no longer a matter of life and death for many FM stations the way it was 10 years ago. FM stations are making it on their own now, and many are making it in the big leagues. The FM -FM quadcasts that have taken place so far raise another interesting question: what is the optimum microphone placement for quad recording and broadcasts? In three (continued on page 86) FRONT L INPUT F INPUT L +F +B OUTPUT L. LEFT R r RIGHT F = FRONT B =BACK LEFT -,LEFT RIGHT Ho -r. COM HOT OCTOBER 1970 R +F -B OUTPUT -lam+ 35 www.americanradiohistory.com MI S3 S4 M2 SI RI S2 s R 8 PREAMP I + S6 R15 S5 R8 PREAMP4 Build modular JI R8 J2 ON-OFF R7, MONITOR J3 R8 J4 PREAMP2 RIO PREAMP3 6-channel stereo mixer preamp by GEORGE D. HANCHETT, Senior Engineer, RCA Solid State Div. THIS STEREO PREAMPLIFIER AND mixer is particularly interesting to those who want to make high-quality tape recordings. The preamp has four microphone and two line inputs that can be switched to left, right, or both channels. In addition, two auxiliary inputs are provided, one for each channel. The auxiliary inputs cannot be switched. All inputs that can be switched are controlled from the front panel. The two auxiliary inputs are controlled from the rear of the unit. Each output channel has its own VU meter. The stereo preamplifier and mixer is made up of three basic circuits and a minimum of inter- connecting wiring. The three circuits are a high -dynamic -range microphone PARTS LIST (Fig. 1) Cl, C2-1000 F. 25 volts, electrolytic D1 through D8- SK3030 (RCA) Ml, M2-VU meter R1, R2, R7, R10, R15, R16- potentionmeter, 10,000 ohms (R7, R10 is a dual linear pot) R3, R5, R6, R12, R13, R14- 10,000 ohms, '/2 watt, 10% R4, R8, Si RRth91r-o31u-3g4h7ohoSmhm6s,s-,'r/o2'/t2awrwaytat,tts,1w01i%t0c%h, 2 poles, 5 J4- positions, shorting type J1, J2, J3, microphone jacks J5, J6-phone jack J7-4 -lug terminal strip (screw terminals) J8, J9 -phono jack 36 SK3030(4) OUTPUT A OUTPUT B V 1,15 J6Iv VU METER A T DI D3 Y MI D4Y D2I R4 47 bAB SI n o 0 o4-r oB I ol 11 R5 10K 0R6 10K LINE AMPLIFIER A (F16.8) R7 10K 10 \ 11 MULTI- INPUT MIXER A (F16.51 1 2 34 5 6 7 MASTER GAIN LINE AMPLIFIER 8 (FIG.8 ) RIO O 10 MULTI -INPUT MIXER B (no.5) I 2 34 5 6 7 SK3030(4) VU ID5 METER Y D7 e RII =D8 47 YD6 M2 S6 TAB A ° ° ° B 1n o- ERIK IOK 01 0.1, o LINE INPUT A J7 -b RI 10K R3 IOK R2 10K J8 AUX INPUT A ABO S2 o B o ti-Lo 5 6 HIGH DYNAMIC RANGE ABO S3 A_o4_ Bo f o o (1) 5 (1) HIGH DYNAMIC RANGE PREAMP A2 ( FIG.2) +20V tR8 33 i1 33 II + Cl C2+ T _L EACH 1000/25V 6 5 HIGH DYNAMIC RANGE R14 IOK AB1 S5 ° B ow-t, ()5 ()6 HIGH DYNAMIC RANGE PREAMP B2 (FIG.2 ) LINE 7 -a INPUT B R15 10K R13 10K SRI6 IOK J9 AUX INPUT e RADIO -ELECTRONICS www.americanradiohistory.com preamp, a multi-input mixer, and a headphone or line amplifier. A block diagram of the total unit is in Fig. 1. The output of each microphone preamp (see Fig. 1) is fed to a switch which can connect it to channel A, the left channel, channel B, the right channel, or both channels (A and B) simultaneously. The output of these switches as well as the line input for each channel is fed into the multi -input mixers. A master gain control combines or gangs the outputs from the mixers installed in each channel and passes the combined signal to the line amplifiers. The diode limiting circuit used with each VU meter keeps the meter from being damaged during the charging of the large coupling capacitors in the line-amplifier. Two R-C power-supply filters consisting of R8 and Cl, and R9 and C2 assure circuit stability. Each filter services two microphone preamplifiers. The stereo preamplifier and mixer is made up of a number of circuits as described above. The description of each of the three circuits includes circuit boards and component placement diagrams. The individual circuit boards and the interconnecting wiring required for the stereo preamp CIRCUIT BOARDS A complete set of 8 circuit boards needed to build this unit are available for $10. Order 10706 -1. A set of 4 boards for building a mono version are $6. Order 10706 -2. Boards are G-10 glass-epoxy, undrilled. Photo negative for making your own boards containing all board patterns is $1.50. Order from Photolume Corp., 118 E. 28 St., New York, N. Y. and mixer may be assembled as desired by the builder to form the kind of custom unit he needs. The high-dynamic-range microphone preamplifier, intended to be used with low-impedance dynamic microphones, will handle loud passages of music and close talking without adverse effect on the output. The amplifier has a gain of 1500 to 2000 and can provide a maximum undistorted output voltage of 2 volts rms to a load impedance of 500 ohms or more. The maximum undistorted input is 400 mV rms. The frequency response is flat from 20 Hz to 30 kHz. The circuit for the high-dynamicrange microphone preamp are in Fig. 2 The preamplifier consists of two stages of current-stabilized amplifiers separated by a gain control and an R-C filter, consisting of R7 and C5, that prevents motorboating. Resistors R5 and R12, placed in the emitter circuits of transistors Ql and Q2, improve the frequency response of the preamplifier by providing some emitter degeneration. The output of the preamplifier is shunted with resistor, R15, to make the circuit compatible with the zero-point switching capability used in the master preamp. The output impedance of the preamp is low. The table shows the value of Rl to use with microphones of various impedances. The printed-circuit -board layout for the microphone preamp is in Fig 3. A photograph of a completed board showing parts placement is in Fig. 4. All ground connections in this circuit must be made to the same point, as shown in Fig. 3, to avoid forming ground loops. This common -ground feature is built into the printed-circuit TABLE I Microphone Impedance R1 (ohms) 200 500 4,000 220 560 R1 not used R1 connected across microphone input jack. Modular construction lets you build a custom mixer -preamp that meets your needs precisely, or duplicate the unit described here 8208 R7 R2 R4 í100K IOK I0/6V 10 /15V CI C3 I 1( ' C4. 100 R3; 01 /25 1+ Oa 6.2K :RI* SK 3038 R5 680 C2 300 /6V+ R6 T 47012 I -*SEE TEXT AND TABLE R9 IOOK C5 10/ 2V R8RIO ít6.2K I0K S 30 csr /RII 10K 02 SK3038 R12 68n 0 %{ 4R713 12 +20V o 6 Q3 K3020 50/I5V +CI(7 4 /RIK1 íR15 OUT I0K 4Q VOM GND PARTS LIST (Fig. 2) CCC32l,-, 1CC065F--13,00105FFv,,o6lt6sv,ovletoslle,tsce,trleoecllyettrcioctlryotilcytic CC74--51000FF, ,1525vovlotslt,s,eelelectcrtorolyltyictic Ql, Q2-SK3038 (RCA) Q3- SK3020 (RCA) RI-see All Resistors 1/2 table I and text -watt 10 %. R2, R9- 100,000 ohms R3, R10-6200 ohms R4, R11, R15- 10,000 ohms R5, R12-68 ohms R6, R13-470 ohms RR78--8p2o0teonhtimoms eter, R14-1000 ohms 10,000 ohms, audio taper OCTOBER 1970 n+ INPUT G O HIGH DYNAMIC RANGE MICROPHONE PRE.AMP FIG. 1- (FACING PAGE) BLOCK DIA- G2-R(ALMEFTo)f complete mixer preamp. MICROPHONE PREAMP FIG. sche- m3fo-ar(tBictEh. eLOThmWrie)keeCItpRrarCenaUsmiIsTpto.BrsOFIAGaRr.eD4uP-s(AeAdTB.TOEFVRIEGN). PHOTO OF ASSEMBLED BOARD ing parts placement details. show- + 42 C 51582I iJAG+62 a I- ' O ' 37 www.americanradiohistory.com board and must be followed if some method of circuit construction other than the printed board is used. In addition, all preamplifier connections to external circuits should be made to the same ground point. Mplti -input mixer The multi -input mixer is designed to mix the inputs from up to seven sources, usually microphones, for input to an amplifier, recorder, or other piece of audio equipment. The mixer has a gain of approximately unity and, therefore, has no effect on the system in which it is installed. If more than seven inputs are required, as many as three mixers can be wired in parallel. How it works The circuit for the multi-input audio mixer is in Fig. 5. The resistance network shown at the left not only provides the mixing function but also to make possible zero-point switching of the inputs. In the zero -point switching, as used in this unit, the capacitors at the output of the microphone preamps as well as the input capacitor of the mixer are kept charged. This is done by connecting a resistor across the output and input. Thus there is no disturbance, no cracks or pops, when inputs are switched in or out. The amplifier portion of the circuit, shown at the right in the schematic, is current stabilized by the emitter resistor. This resistor is not bypassed, and provide a greater degree of degeneration and reducing the overall gain of the mixer to unity. Some adjustment of resistor val- ues is required if less than seven inputs are used. Table II shows these re- TABLE II RESISTANCE VALUES No. of inputs 2 3 4 5 6 7 R17 8.2k 7.5k 6.8k 6.8k 6.2k 6.2k R18 120 ohms 110 ohms 91 ohms 82 ohms 75 ohms 68 ohms sistor values for from 2 to 7 inputs. When three or more mixers are paralleled to accommodate more than seven inputs, not only must the outputs of the mixers be paralleled but the ground points on each circuit board must be connected. The gain of the mixer thus connected is somewhat less than unity. Component placement and circuit board pattern for the multi -input mixer are in Figs 6 and 7 along with a photograph of a completed board. Headphone or line amplifier The headphone or line amplifier is very useful when the power amplifier is located some distance from the microphone. If preceded by a microphone preamp, the amplifier makes a very useful remote pickup. It is also very useful for driving the line inputs of tape recorders. The headphone or line amplifier has a voltage gain of 100 and can drive any line impedance of 250 ohms or more. It has a maximum undistorted output of 3 volts rms into a 500 -ohm line and has a frequency response fiat from 20 Hz to more than 25,000 Hz. The input impedance is 1,800 ohms. Amplifier operation The circuit for the headphone or line amplifier is in Fig. 8. The interconnection of the transistors in the + 20v R15 R14 R12 RIO RB R5 R6 R4 R3 FIG. 5- (BELOW) unit described in audio mixer. FIG. CIRCUIT of 7th-is(ABaOrtiVcEle). multi FIG. -6in-p(uRtIGaHuTd)io mixer. Two are CIRCUIT BOARD needed to build PATTERN for the the PHOTO OF MIXER shows parts placement on the circuit board. Refer to Fig. 1 for interconnection details of the complete preamp. I 2 3 4 O O 6 7 0 10/6 10/6 10/6 -10/6 10/6 10/ 10/6~-6 C6- V V R1 CI+._.R3 C2 +TR5 C3 V V C4 =---' V C5T R7t + R9 RII V V C7 R13{{ R15 IK IK IK IK S IK IK IKS I I R2 R4 R6 R8 RIO# RI 2t 39K# 9K 39K 39K 39K' 39Kí +20V O9 -CIO 0OUT I *SEE TEXT AND TABLE SE COM 12 38 www.americanradiohistory.com PARTS LIST CC8l-t5hr0ouFgh, C7 -10 (Fig. F, 6 5) volts, electrolytic 15 volts, electrolytic Q1-SK3020 (RCA) Rl, R3, R5, R7, R9, R11, R13-1000 ohms, 1/2 watt, 10% R2, R4, R6, R8, R10, R12, R14- 39,000 ohms, 1/2 watt, 10% R15- 100,000 ohms, 1A watt, 10% R16-2200 ohms, 1/2 watt, 10% R17, R18 -see table II and text RADIO -ELECTRONICS +20V R2 3.9 K lo IN 2 COM CI SK3020 5/6 02 SK3024 5C2 100//225 C OUT 4COM 3 PARTS LIST -5 C1 C2 -10F0,F6, (Fig. 8) volts, electrolytic 25 volts, electrolytic Ql-SK3020 Q2-SK3024 (RCA) (RCA) RRR213--13-609800000,00oo0hhmmoshs,m, s1%/,/22 watt, 10% watt, 10% '/2 watt, 10% R4-470 ohms 'A watt, 10% o COM a o wz oc o zLU _ao to _ za. OUTPUT 10 (46 A g A 8 LINE INPUT A AUX INPUT e s iaFnlRlpOuliktMejlayTcHkasEp. pRTlihcEraAetReionsOse.Fts THE MIXERPREAMP you of outputs were connected can see the auxiliary in parallel to provide input and line connectors for Ci Oi FIG. uses 8 -(TOP) LINE two transistors. AMFIPGL. IF9IE-R(CEcNirTcEuRit scAtFhhiIBreGocOwu. lViiintn1Ege0b)o(apAaCradmBIrRtOspinCVlitfUeEpierlI)aTcrcoeCnismBnOeOeMscnAhPttoi.RoLwnDESnseT.eEpaDcaFttiutgeBa.rlOn1AsRiffzooeDrr. STANCOR TP -3 PRI 120 VOLTS SEC SO VOLTS SK3030 D3 22V ZENER WATT COMMON FciIrGc.uit.11-PItOWis EbRuiltSUrPigPhLtY is on regulated the main chassis of the mixer reamp see in the photo at the right. as you can OCTOBER 1970 LrcioOgnhOstiKstoIsNf GotfhelIeNapdhFsoRtcoOo.MnTnehTecHtiEntwgTooOuVPtUpuyotmsuettcoearntshesaerceeirtcahuteitthpbeoowaterodrp-s.s.uMpposlyt components in of the jumble the lower of wiring amplifier makes the operating condition of the amplifier self-adjusting, (i.e.: the amplifier can maintain itself in a stable operating state in spite of variations in power-supply voltage and ambient temperature. Stability is insured by feedback through R3. If ()Ps emitter current should increase, the base voltage of Q2 would decrease because of the additional voltage drop in R3. However, the decreased base volt- age of Q2 results in a drop in Q2's emitter current, a reduction of feedback voltage to Q1, and hence a decrease in QI's collector current. This decreased collector current causes an increase in Q2's base voltage that compensates for the original decrease and the amplifier is stabilized. The interconnection of transistors just described also makes possible the low output impedance of the amplifier. The printed circuit board pattern for this circuit, and a photo of a completed board, are in Figs. 9 and 10. Power supply is last A simple power supply completes the unit. This supply is shown in Fig. 11. It is assembled directly on the chassis of the unit and is not built onto a circuit board. Once you have completed the power supply, selected the desired number of input, mixer and output boards you can proceed to assemble your custom mixer-preamp. We are sure you will enjoy it. This article is presented through the courtesy of the RCA Solid -State Hobby Circuits Manual, HM -91, $1.95, which will be published early this fall. R -E 39 www.americanradiohistory.com Get better from your A do-it-yourself guide to maintenance and simple adjustments to get the best from your stereo rig. by PETER SUTHEIM This article is one of a series intended as a sort of supplement to the operating booklet that comes with hi -fi components. The manuals are often pretty short on information that doesn't have to do directly with turning the unit off or on, using the controls, and such basics. Since most customers for hi -fi components are not at all technically inclined, the makers feel it's pointless to take up space describing maintenance and the more subtle adjustments. But for those who enjoy getting a feel for the equipment they use, the warning, "no user-serviceable parts inside" does not need to apply. One caution before we begin, though. Nothing in this article is in- Harman-Kardon's Citation 12 120 -watter. The latest in stereo power amplifiers. 40 tended to contradict anything in the instruction manuals. We may suggest occasional lubrication, for example; but if your booklet says very explicitly not to oil this or that, then don't oil it. They know more about what they've made than you do, or than we do. This month we discuss tuners and amplifiers. Later we will cover such components as speakers, record players and tape recorders. Keeping the amplifier fit Well-designed transistor amplifiers tend to deteriorate a lot less with age than tube amplifiers do, partly because of the inherently long life of transistors when they are not abused, and partly because of lower voltages and lower temperatures in solid -state equipment. There is usually not as much preventive maintenance to do in solid -state gear. It is important, though, especially in dusty or smoggy regions, to clean air vents, grilles and heat sinks. Heat held in by restricted air flow can cause premature failure of transistors and other parts, especially in marginally designed equipment. Use a whiskbroom, brush, rag, or vacuum cleaner. Noisy or intermittent switches and controls can sometimes be fixed by cleaning the contacts. Seldom -used switches and controls are the most likely to cause trouble. Often just twisting the switch or control rapidly from one stop to the other several times is enough. Sometimes you will have to use a switch and control cleaner, or some ethyl chloride, to help dissolve dirt. Inspection of a switch will sometimes turn up the cause for intermittent operation -bent or corroded contacts, dirt, a bad solder connection. A fairly common cause for noisy volume and tone controls in transistor amplifiers is dc leakage through the control. The tendency to use relatively low-resistance controls in solid-state amplifiers (10,000 ohms, for example) requires coupling capacitors of 5 or 10 µF, typically. In all but the most expensive equipment, these are electrolytics, which tend to leak more than other types of capacitor. Leakage also tends to increase with age and temperature. The only answer is to replace the offending capacitors. If you can afford to, use tantalum capacitors, which have far less leakage current for a given capacitance. Many early solid-state amplifiers and preamps had objectionably noisy phono preamp stages. It is sometimes RADIO -ELECTRONICS www.americanradiohistory.com sound STEREO PHASE INVERTER DC BALANCE ADJUST \ R4 POWER OUTPUT OUTPUT TRANS R2 AC R3 (DRIVE) BALANCE BIAS SUPPLY R5 BIAS VOLTAGE ADJUST B+ Fig. 1-ADJUSTMENTS ments. Usually, R2 plus the de bias level, while IN HI -FI AMPLIFIER. Not all amplifiers have all these R3 equals RI. Pot R3 sets equal drive to tubes V! R4 sets equal cathode currents through R6-R7. and V2. adjust- R5 sets WATCH FOR SYMMETRICAL CLIPPING AUDIO OSC AMPLIFIER UNDER TEST possible to improve them with newer transistors. The General Electric or Sprague 2N3391 -A is a good, low noise, low -cost silicon planar npn transistor now being used by many manufacturers; it can replace other silicon npn types probably without any changes in circuitry. An even better transistor is the Fairchild SE4010, though it may be harder to come by. Both cost well under $1.00. Several designs used the RCA 2N2613, a pnp germanium transistor especially recommended for low noise. Performance was sometimes disappointing; buying a handful of 2613's and finding the one with the lowest noise may bring significant improvement. A possible replacement is a silicon pnp transistor by Fairchild, the 2N4250 (or its brother and sister, the 2N4248 and 2N4249) . Depending on the circuit, this may require some changes in first-stage bias-resistor values. Its gain is very high even at collector currents around 10µA, where noise is extremely low. The 2N424850 series also cost well under $1.00. Sometimes replacing first-stage emitter, base and collector resistors with some of better quality helps. Any resistor with dc flowing through it is a OCTOBER 1970 SET TO 400 Hz OR I,000Hz APPROX 8-OHM WIREWOUND DUMMY LOAD RESISTOR (GETS HOT I ) VOLTMETER TO MEASURE OUTPUT (VOLTS) 2 POWER 8 (ASSUMING AN 8d0 DUMMY LOAD) Fig. 2-POWER AND OUTPUT BALANCE CHECK. Assymetrical by balance adjustments is probably developed in earlier stage. put, adjust the 400- or 1000 -Hz input signal to just below point on scope. Square the voltage reading and divide it by the value clipping not correctable To measure power outwhere clipping is seen of the load resistor. potential source of extra noise. Oh- mite, IRC or Allen- Bradley com- position resistors are likely to be better than unknown or "bargain" resistors. It is impossible to tell by looking at a resistor how noisy it is, so pulling out resistors and replacing them with new ones is a gamble. But it may be worth the effort if you are annoyed by hiss. If yours is a tube amplifier, much of what has been said about cleaning applies to it also. If the tubes are more than about 3 years old, replace them. Use matched pairs in output stages unless your amplifier provides dc balance adjustments. Run through the balance and bias adjustment (Fig. 1) in any case; follow the manufacturer's instructions. The idea is to get the two push -pull output tubes in each channel to draw equal current through the output transformer primary winding. Since the currents drawn by each tube flow in opposite directions, the magnetic fluxes they generate in the transformer core cancel each other. This reduces distortion and extends the bass power capability. Several tube amplifiers provide metering terminals or some other way of adjusting output -stage current. Another good way to check is to set the amplifier up for a power measurement (as in Fig. 2-400- or 1,000-Hz tone to the input, 8 -ohm resistor and scope across the output), and adjust the tone level and the output-stage balance until the clipping of the output waveform is symmetrical. Still a third way is to connect a harmonic distortion meter to the amplifier output and adjust the bias and balance controls for minimum distortion at a power output near the rated maximum. A few amplifiers have adjustments for balancing the signal drive to the two sides of the push -pull output stage (Fig. I again). These too should be checked after the tubes are replaced, and checked again after the first hundred hours' use. The symmetrical- clipping test can be used here, but the best way is to adjust for lowest harmonic or intermodulation distor- tion. If an amplifier does not meet its power or distortion specifications (at rated line voltage) after you have replaced its tubes, perhaps some resis- tors have drifted off their original values, paper capacitors have become leaky, or electrolytics have become inefficient. If you can, check supply voltages against the schematic. They 41 www.americanradiohistory.com should be within 10% of their specified values. If they seem low, and you know your line voltage is normal, replace the electrolytic filter and decoupling capacitors. This should also help cure hum or instability that may have developed over the years. But don't be too hard on an old amplifier. First of all, remember that a 10% drop in power (as from an original rating of 20 watts down to 18) is only t/2 dB, and completely inaudible. A loss of even half the power (3 dB) may not be noticeable in many situations. Secondly, many amplifiers were (and are) sold on the basis of exaggerated or "best of the run" figures. If this is the first time you've made measurements on your old amplifier, you may be discovering that it never did perform as well as you were led to believe. The noise level of the pre- amplifier stages can vary enormously with the tube used. Not all 12AX7's are the same. By general consensus in the industry, the quietest are the ones made by Telefunken in Germany; several manufacturers imported them for inclusion in original equipment, often stamping them with their own brand names. Such premium tubes may be available as replacements if you write to the manufacturer. Good bets also are the ECC83 tubes (European type number corresponding to the American 12AX7) made by Mullard (British) and Amperex (Dutch). The American premium versions of the 12AX7 never quite came up to the standard set by the European types, although the G -E or RCA 7025 may be worth trying. If you have the money and the patience, buy several and find the ones that have the lowest hiss, hum and "flicker noise ". If your amplifier uses 12AX7's in tone-control or other later stages as well, you can safely use the noisier tubes there, where the signal level is higher and less susceptible to tube noise. Tuners For tuners with vacuum tubes, replace all the tubes if they are more than about 3 years old. In all tuners except the Marantz 10B, which uses i.f. filters instead of tuned trans- formers, it would be wise to follow tube replacement with an alignment job. FM alignment, especially in a stereo multiplex tuner, is much more critical than AM alignment, and the safest procedure is to follow the manufacturer's service instructions. In general, though, you can check i.f. alignment easily enough by tuning in a weak station, or by weakly coupling a signal generator to the i.f. strip. Assume, if you use a generator, that the i.f. strip is basically tuned to 42 the correct frequency (that is, 10.7 MHz). It is probably more accurate than your generator, so connect a vtvm (switched to a relatively low dc range) between the last limiter grid and ground, and introduce a weak signal from the generator. Then tune the generator until the meter peaks (or until the tuner's own signal-strength meter peaks). Don't worry if the generator's dial reads something other than 10.7 MHz. This way you'll avoid the risk of unnecessarily realigning the whole i.f. strip to a new frequency, with possibly very evil effects on the tuner's performance. It is important to use a weak signal for peaking the alignment of an FM i.f. strip. Strong signals will cause limiter stages to saturate, and when they do, their tuning characteristic will be very broad and the peak hard to find. You can also use a weak FM broadcast station for the same purpose. Aligning the detector in a highquality tuner is more difficult, and best done with a sweep generator and a scope, with the help of the manufacturer's service manual. It is best to leave the ratio detector or discriminator alone unless you have reason to believe that it's seriously out of whack (if, for example, there is audible distortion on almost all FM stations, or if you've diddled with the alignment already). Fig. 3 shows a RATIO DET TRANS 7--.4,--oR 6AL5TUBE I I¡ I I MPX OUTPUT MONAURAL AUDIO OUTPUT = SET VTVM TO LOW DC VOLTS RANGE, ZERO POINTER AT CENTER OF SCALE, CONNECT AS SHOWN Fig. 3-TOUCHING -UP FM DETECTOR. With input from FM generator or station, adjust secondary slug for zero output. quick "field expedient" method for at least "centering" the detector with a signal generator or FM station as the signal source, and a vtvm. If the dial calibration is off, check to see whether it's off by a linear amount (a certain fraction of an inch) all the way across the dial. If so, the error is probably due to dial cord slippage, or some other kind of mechanical slippage. Slipping dial cords can often be restored just by cleaning them with a greaseless solvent, like isopropyl alcohol or ethyl chloride. Or perhaps the pointer has simply slipped slightly. Even if it hasn't, you can sometimes restore dial calibration reasonably well by sliding the pointer to the correct spot on the dial when the tuner is centered on a station whose frequency you know. (Remember that FM broadcast station frequencies are far more accurate than service-type signal -generator calibra- tions.) If the calibration seems to be pre- cise at one end of the dial or in the middle, but off by an increasing amount elsewhere, the error is almost certainly due to a drift of value of some component in the oscillator tank circuit. It is often possible to restore accurate calibration by juggling very slightly the adjustment of the os- cillator coil and the oscillator trimmer, but this can be tricky and time -con- suming. Under no circumstances make any gross adjustments unless you know exactly what you are doing and why you are doing it, otherwise you may have a full -scale alignment job on your hands. If the error is not serious it is sometimes better to play it chicken and live with it, or to move the dial pointer slightly to "split the difference" in the calibration error. If you choose to replace the dial cord altogether, be sure to make an accurate sketch of how it is installed before you remove the old cord, else you may have several hours' intensely frustrating work ahead. Unless you have had experience, leave the multiplex section alone. Any kind of alignment work on a multi- plex decoder requires at least an accu- rate source of 19-kHz and 38 -kHz sig- nal. The procedure is too long to go into here. Numerous books and arti- cles dealing with the adjustment of stereo multiplex decoders have been published. Many complaints of poor FM re- ception are due not to the tuner but the antenna and lead-in. An outdoor antenna should be inspected at least once a year, especially in industrial areas where corrosive pollution runs high, or in seacoast locations. The poly- ethylene insulation of twin-lead dete- riorates with exposure to sun and air pollutants, and its electrical loss in- creases. Connections between the lead - in and the antenna or lightning arres- tor can corrode and break. Insulating blocks on the antenna itself can be- come coated with conductive salts, greatly decreasing the effectiveness of the antenna. Other things change with time, too; a new tall building may have al- tered reception conditions in your home, and that could be responsible for worsened quality on some stereo stations. A change of antenna loca- tion, or à different antenna, may be needed to solve the problem. R -E RADIO -ELECTRONICS www.americanradiohistory.com TAPE RECORDING how to buy audio tape There's more to magnetic tape than the box it's packed in. Here's the story on what goes into those white boxes. by BYRON G. WELS YOU'VE BOUGHT YOUR FIRST TAPE RE- corder, and now you want to buy tape, so you can put it to use. You're faced with a fantastic assortment of brands, types, lengths, thicknesses and prices. Chances are, if you're like most people, you will try a bit of this and a bit of that, until finally you learn what you like and what you don't like. However, although this process works, it is horribly expensive. You can often get stung by the cost until you learn, and more costly, you might even entrust a valuable recording session to a shoddy tape and wind up losing money and recording. In this article, we will outline what to look for and what to look out for in tape, so if you do spot a bargain and go for it, you'll at least know what you're getting and won't be surprised. Prerecorded tapes The newcomer (and many old hands) at tape recording look upon a tape machine more as a means to play music than to record it, and this is fine. These people invest in "albums" of prerecorded tapes, collecting the music they like. But you've got to be on your guard. Today, most tape albums are sealed in plastic wrap, and you can't open the package to look at what you're getting, let alone listen to the tape before you buy! The best rule here is to know what you are buying beforehand. You can do this by listening to your better FM music stations, those that announce the name of the tape producer and the number of the tape either before or after OCTOBER 1970 playing. This gives you the chance to listen and judge in advance. Another good rule is to stick to the names you know, both in producers and performers. Because artists' fees are high, some of the smaller music producing companies will go abroad and hastily organize a "pickup" symphony orchestra to play into a recorder. This master tape is then brought back home for processing, duplicating and sale. Such tapes can be spotted by the fact that the box will rarely mention the performing orchestra, featuring the title of the work for a big play instead! Somewhere on the box, if you can find it, the orchestra will be identified. But if you spot a name like the "Lower Slobovia Penultimate Symphonette," watch your step. Another thing to watch for are certain key words. "Suite" and "Excerpts" both imply abbreviated versions of a work. Unfortunately, we often accept such words as part of the actual title. However, "Swan Lake Ballet Suite" means a shortened version of the full ballet. The word "Suite" is French for fast. Another trick word is "Overture" or in French, if you want to add class to your record or tape box, "Ouvreture." This is really just an introduction, not an entire opera. Finally, take a look at what you've bought when you get home. Maybe you bought a box that's a full 7 inches across, and maybe it contains a reel 7 inches in diameter, but you might find a huge plastic hub at the center, up to 4 or 5 inches across. The result? A heck of a lot less music than you expected! If you can get stung with re- corded tapes, the problem is even worse for blank tape. Let's take a look at what's generally available. First, you've got to choose your base material. This is the plastic on which the oxide recording medium is applied. You have a choice of acetate or Mylar, in varying thicknesses. The acetate is more prone to breakage and embrittlement, unless you go for the thicker base. Of course, using a thicker base means that they can't put quite as much tape on each reel! The Mylar is far longer -lasting and in the thin 1/2-mil and thinner 1/4-mil varieties you get a lot more on each reel. Of course, you pay more, and if you set the record level too high you may get print through. That is, the recorded information on the tape is transferred to the next layer, with all kinds of echo effects that were never recorded in the first place! More critical is the oxide itself. How well has it been designed, how well has it been milled, and how good a binder has been used in making it adhere to the base? These are all critical factors. Why? If the oxide hasn't been properly milled, it will be lumpy, and each lump will make the tape rise from the head, causing dropouts in your recording. If the binder isn't good, the oxide will shed, again leaving blank spots in your tape. It can also speed head wear. Chances are that if you buy a name brand, you'll get good quality. Your choice really depends to a great extent on what you plan to use the tape for. But you also ought to select your tape to fit the application in light of what that application is. If you anticipate recording level problems, use a high-output tape. If 43 www.americanradiohistory.com you're going to be recording long sessions with no opportunity to clean the heads, use sandwich tape, in which the oxide is sandwiched between two layers of plastic, the top layer being very thin. No oxide touches the heads, so there's no need to clean. White -box tape As Barnum said, "There's one born every minute." White -box is tape that is usually sold in a plain white box, with no manufacturer's name or reputation to back it up. It's usually sold at a comparatively low price, and usually there are more than enough customers ready to shell out their money for this stuff. What white -box tape is, however, is a story in itself. Usually it's computer tape that was 1 or 2 inches wide and reslitted to the required 1/4 inch. Unfortunately, computer tape is required only to register the fact that it has been magnetized or not magnetized. The fidelity of this stuff is often not suited to audio work. Sometimes, white-box is reslitted video tape, which has a better frequency response but can bring other problems. The safest rule is to stay away from this stuff. Another good source for the white-box packagers is mill ends or rejects. When a tape manufacturer starts or finishes a run of tape he must adjust his coaters. Until they are set properly, quality will suffer. However, he can and does sell these mill ends or rejects to the white -box people. Fortunately, many tape manufacturers have begun to realize that they are actually doing themselves a disservice by this practice, and simply throw away the subgrade material. Testing tape The proof of the tape pudding is usually in the playing, but there are tests that you can use to find out how good (or bad) a reel of tape is. One good test is to take a look at the new reel of tape, holding it up to an even, strong light. The layers of tape on the reel should be smooth and even, with no sign of buckling. If you see a slight "hump" in the tape, unwind it to that point to see whether you've got a buckling overwind or a splice. Next, unwind about 4 or 5 feet of the tape in a room where the air is quite still, and let it hang from the reel. If the tape does not hang evenly, with no "pulling" to either side, this indicates that the tape slitters were dull and that the tape has "warped" as a result. Such tape may jump the idlers during a session. Next, draw the tape tightly over a straight edge, such as a table edge. Look carefully for any sign that the oxide has flaked off. As a final test of shedding, place the tape on a flat surface, oxide side up. Press a piece of pressure-sensitive tape over the oxide, and pull it away quickly. Examine the IF OXIDE FLAKES OFF when you run it over a table edge, it could be a bad buy. tape carefully under a good light to see if any oxide pulled off. Tape recording is a wonderful hobby, but it can be marred by a poor purchase. Know what you're going to buy, and then go to the store and buy it. Remember, you're buying tape-not fancy four-color packages, not low prices-just good, high-qual- ity recording tape. And watch out for glib, smooth - talking salesmen, too. They do not al- ways have your best interests at heart! Some stores give the salesmen what are called "P.M.'s" or Push- Merchandise bonuses. If they sell products so listed, it's more money in their pockets, so don't be fooled. More than anything, else, re- member to Caveat the heck out of Emptor! R-E MODULAR TV SETS (A rundown of the new sets) MOTOROLA (TS- 915 -'19) Cuasar Solid State Color Panel AFC B D E F G H L M S Circuits AFC discriminator & amplifiers Video IF amps., AGC amp., video det., video det amp., 4.5 MHz det. Audio demods, & output amps. Noise inv., AGC gate, sync sep., vert. sync inv. & oscillator, 1st video amp., 2nd video amp., brightness stabilizer Color gate pulse former, horz, osc., horz. output Vert. pincusion amp., H. reg. amp. & driver Vert. limiter & Vert out., vert. and horz. convergence assy. RGB demodulators, RGB video driver, blanker amp., blanker out., brightness controls RGB video out. amplifiers & drive adjust. ACC amp., color killer amp., color IFs, color oscillator output & drivers MOTOROLA (Hybrid) CTV5, CTV6 Quasar 2 Color ZENITH (Hybrid) 4B25C17,19 Color ZENITH (Hybrid) 12B14C52 Color 44 BA Video IFs, video amp., audio IC, audio out. FA Sync. sep., vert. osc. /out., H. phase det., horz. osc., hors. driver HA Convergence assembly KA AFC discriminator & output SA Color sync & osc, col. killer, ACC amp., 2nd video amp., sync & AGC takeoff, color IFs, RGB demodulators, volt. rg., RGB video outputs ZA Transistor supply regulator (+20 volts) with foldback current limiting Panel Circuits 9 -23 (AGC Module) AGC gate, AGC delay, AGC output, noise gate driver, noise gate, sync limiter 9 -27 (SubGen. Module Assy.) 9.37 (Chroma Mod.) 150 -166 (IF Assy.) S -85579 (Cony. Assy) 9 -47 (Color Module) IC subcarrier oscillator, APC, ACC, output amp. IC chroma ampa. & IC demodulator Three IFs, Audio Det., Video Det., 1st video amp. Dynamic convergence assy. . 2nd color amplifier & IC demodulator ZENITH (Solid State) 22AB55 Monochrome HEATHKIT (Solid State) GR -270, GR -370 Color RCA (KCS 184, 177,176) Solid State Monochrome 150 -20 (IF Three IFs, video det., & driver Assy.) 150 -204 Sound IC demodulator, amplifier (Sound Mod.) 9 -22 (Video- Video out, sound driver, sound output sound Mod.) 9 -23 (Sync- AGC gate. AGC out, AGC delay, noise gate AGC Mod.) driver, noise gate, syn limiter 9 -24 (Vert. Vert. osc., vert. driver, vert. output Mod.) 9 -25 (Horz. AFC, horz. osc., hors. driver Mod.) Panel IF Assy. Circuits Three IFs & video detector, driver Lumi nance Board Lum. Amps., blanker, brightns lim. & control, dot generator Sound Board Video Out Board AGC /Syn Board IC amp.- discriminator, driver, audio out. IC demodulator, lum. amp., RGB outputs AGC inv., gate & gated amp., AGC amp., RF AGC, noise inv., sync gate, sync. sep. Chroma Board Osc. Circuit Board ACC amp., color killer, 1st & 2nd color amps., band pass amp. Burst amp., ACC, APC phase diodes, IC 3.58 MHz oscillator, CW amp. AFT Circuit Board Convergence Board Vert. Osc. Board Horz. Osc. Board Horz. Out Board Panel Pix Module Video Module Sound Module IC amp., discriminator, RLC circuits for dynamic convergence Vert. switch, vert. predriver, linearity clamp, vert. driver Phase slitter, AFC diodes, horz. osc. SCR HV drivers, HV regulator Circuits IF amps, video detector, video drivers, AGC circuits Video out, sync, AGC keyer IC sound det., amp., audio output RADIO -ELECTRONICS www.americanradiohistory.com NEW R -E EXCLUSIVE Focus stages-four major versions in color chassis Kwik- FixTM picture and waveform charts by Forest H. Belt & Associates SCREEN SYMPTOMS AS GUIDES WHERE TO CHECK FIRST SYMPTOM PIC DESCRIPTION VOLTAGE WAVEFORM PART For reference: Raster lines in focus (closeup) Normal Normal Normal Raster out of focus and shaded ( closeup) Focus anode of CRT No help Bleeder resistor No raster Focus anode of CRT No help Focus rectifier Raster out of focus (with picture) Focus anode or CRT No help 100k resistor (diagram B) No raster Focus anode and no tube current No help Focus transformer NOTES: Screen symptoms are only of marginal help in tracking down trouble in focus stages Study the screen as you turn the FOCUS control. Only helpful clues are at the points indicated. THE STAGES All color picture tubes except recent small-screen types require a high dc focus voltage. Its value must be at all times from 18 -20 percent of whatever value of high volt- age is applied. If the high voltage varies, the focus voltage must vary with it. Otherwise, there will be poor focus at high and low brightness. In practice, that means focus volt- age must vary from about 4200 to 5500 volts dc. Color picture tubes use electrostatic focus. This makes a "dry" circuit; that is, there's NO normal current flow to or from the focus electrode in the CRT. The only electron flow in the entire focus stage is a very tiny current where tvhaeluree'-s 6a6 bleeder megs or resistor. more. That's normally a very large Focus voltage is developed by rectifying a high-energy an Easy ReadTU feature by FOREST H. BELT & Associates © 1970 Check focus voltage or horizontal-output cathode current as indicated. For quick check, test or substitute parts shown as most likely cause of the screen symptom you see. pulse taken from the plate of the horizontal output tube. Its value is usually about 5000 volts peak to peak (p -p). The pulse is fed to the focus rectifier anode, usually directly from the horizontal Output plate. Only in an occasional chassis is there a small bit of flyback winding between horizontal output plate and focus rectifier. The stage in diagram A has the control potentiometer across part of the flyback winding. The pot slider picks off enough of the pulse to develop the correct value of dc at the output of the 1V2 focus rectifier. This version is seldom used anymore. Diagram B is popular in middle -age color sets. Sometimes a solid -state rectifier is used in place of the tube. The distinctive part is the focus transformer, which has a movable core in part of the windings. The rectifier anode is www.americanradiohistory.com DC VOLTAGES AS GUIDES Voltage change to zero very low low slightly low slightly high high - Diagram A V1 cathode Normal 20% of HV R1 open Vi open Diagram A focus anode lead Normal20 %ofHV R1 open R2 open V1 open R1 leaky * V1 socket bad R1 faulty* R2 arcing* CRT socket (pin9) R2 v. high R3 open Diagram B V1 or X1 cathode Normal- 20% of HV V1 open X1 open V1 socket bad T2 shorted Cl shorted X1 shorted T2 shorted T2 open R1 open CRT socket (pin 9) R3 open R2 high Cl open - Diagram B focus anode lead Normal 20% of HV R2 open R2 v. high Diagram B - H -O Tube cathode current Normal 200 -240 mA Diagram C focus anode lead Normal- 20% of HV R1 open R1 faulty Cl shorted T2 shorted X1 shorted R2 faulty: R1 open R2 faulty* R3 open Diagram D focus anode lead R1 open R2 open R1 v. high R2 open R3 open NOTES *erratic voltage usually depicts internal arcing. Use this guide to help you pinpoint the faulty part. Measure each key voltage with vtvnz and high- voltage probe. Measure key current with current function of vorn. For each, move across to the column that best describes the change you find. Notice which parts the chart says might cause that change. 46 Finally, notice which parts are repeated in whatever combination of voltage changes you find. Test those parts individually for the fault described. NOTE: Use the chart rows for the diagram closest like the focus stage you're servicing. NOTE: All these voltage guides assume the high voltage is within 1000 volts of normal. RADIO -ELECTRONICS www.americanradiohistory.com driven from the horizontal output plate, as in other focus stages. The focus-transformer windings are fed out-of- phase with each other, and at a different phase than the voltage pulses at the rectifier anode. The adjustable core determines how much and what phase of pulse is fed to the rectifier cathode through the 130-pF capacitor. The net dc at the cathode depends on the relative values and phases of pulses applied to the rectifier. The core adjustment there- fore in effect controls dc focus voltage. Some early models -and ones -use a focus stage like a few diagram small- screen recent C. A specially built divider voltage resistor source. develops focus dc directly from the high That takes care of tracking very simply; focus voltage is automatically a fixed percentage of the high voltage at all times. A high-value potentiometer at the ground end of the bleeder provides manual adjustment. In diagram D, a voltage sextupler, of the half -wave vari- ety, builds an input pulse voltage into the 25 kV dc needed for the color picture tube second anode. A tap in the volt- age multiplier picks off about 30 percent of the total volt- age value for exact value of focus. Divider dc sent to the resistors and a pot set CRT focus anode. This the ver- sion is found in recent-model solid-state color receivers. SIGNAL BEHAVIOR There is only one "signal" or waveform in any of these focus zontal stages. output That's the tube plate. high- energy It is above pulse 5 kV from the horip-p, far beyond the rating of almost any scope or probe. You seldom need to know its voltage, anyway. If you want to view the pulse waveform, clip the scope probe tip to the insulation of one of the leads. from the plate cap of the horizontal output tube The lead is fine, if the connection is direct. no NOT LET THE PROBE TIP TOUCH sbothhafaecpiktets.eIralmfenadaidnssafiolzsc(esueosaesrtrtWwhaeniansvcdfoeoinfrroegmrsimes orafGdisjtuuhuisesdteeedfd)o,.ctvuhsae-riteprsaunlscseofontrsamikdeeenrraboatlryofnliyne- DC DISTRIBUTION Actual dc voltage in a focus stage that given on the schematic for the may be different from chassis. So much de- pends on the particular CRT. But the difference won't be great. A lot also depends on the value of the high voltage. That, in turn, depends on the settings of the screen and drive controls, brightness, and in some sets the contrast. Dc focus voltage is usually fed to pin 9 of the picture tube. There may be a series resistor, or none. Since no current flows, the value doesn't affect dc voltage. The re- sistor is mainly a filter to smooth out any pulse "hash" that gets past the rectifier. To stabilize the load on the focus rectifier and pulsesupply circuits, there is often a bleeder. Changes in its value, or in the values of any resistors in series with it, can alter focus voltage seriously. SIGNAL AND CONTROL EFFECTS Controls are of three main types. One is the potentiome- ter version shown in diagram A. This kind has almost disappeared. It was dangerous because so much hot rf from the flyback was present. The control didn't last long, either. More popular is a different kind of potentiometer hookup, shown in diagrams C and D. A pot in a resistive divider network has a comparatively small dc voltage-. only a few thousand volts, and dc at that. The third type of focus control is the adjustable -core TI HORIZ OUTPUT TO HV RECT RI 100K FOCUS I V2 VI I MEG 22 MEG R3 22MEG TO FOCUS ANODE CRT PIN 9 TI HORIZ OUTPUT TO HV RECT 2 AV 2 D DIODE R2 22MEG II emMit CI 130pF T2 6 kV I 4 MEW I IFOCUS I TO FOCUS ANODE CRT PIN 9 R3 66 MEG 22 MEG VI HV RECT TO SECOND ANODE OF CRT RI 1321 I MEG TO FOCUS ANODE 1 128 L _J MEG 1 OF CRT p- p PULSE R3 50 MEG IN SOME VERSIONS R2 10 MEG FOCUS OCTOBER 1970 www.americanradiohistory.com 25 kV TO CRT SECOND ANODE RI 15.5 MEG -R2 6MEG 4kV -5.2kV TO CRT FOCUS ANODE >20MEG 47 focus transformer (diagram B). Its operation has been explained: it controls dc output of the rectifier by altering the net pulse voltages applied to the focus rectifier. The object of any focus control is to vary the average focus voltage to suit the CRT and the settings of other controls in the chassis. To a small extent, the video in the station signal can affect focus voltage. If you put a dc meter on focus voltage, you'll see it vary with brightness content of the picture. More brightness over the screen loads down the high voltage, so the focus shifts downward enough to track. The high- voltage regulator should take care of voltage shifts, but small changes are normal as scenes change. QUICK TROUBLESHOOTING The quickest way to spot a focus problem is to look at a blank raster on the picture-tube screen. If the set has a SERVICE switch with a RASTER position, use that. Or, turn the AGC control to produce a whiteout. Or, just pull an i.f. tube temporarily. If horizontal scanning lines are not clear and sharp, turn the focus control in both directions. One way should bring the raster to sharp focus. If not, the set has focus trouble. For a first check, measure the high voltage with a normally bright raster. If it is within 1000 volts of the value recommended by the manufacturer, yet the raster will not focus, the trouble is definitely in the focus stage. The high voltage must be within tolerance before you can make any meaningful tests in the focus circuits. That's because, one way or another, the focus stage gets its drive from the sweep-and high-voltage section. Compare the two voltages to their normal values. If the high voltage is, say, 10 percent low, and focus voltage is perhaps 50 percent low, that points to focus trouble. If both voltages are either high or low by the same percentage, the trouble is common to both. The horizontal output tube, flyback, B -plus, boost voltage -all could af- fect the pulse reaching the HV and focus stages. You can measure focus voltage conveniently at pin 9 of the socket for standard color picture tubes. Or, it may be easier to reach at the focus-rectifier socket or terminal, or at the hot end of the 66 -meg resistor. Most high- voltage probes or voltmeters can read focus voltage accurately. While you're near the CRT socket, take a look at pin 9. This terminal often corrodes,-turning green and sometimes eating the wire through. The cure is a new CRT socket, and then fill the pin -9 socket terminal with silicone grease to keep air from it. SPECIAL CLUES If focus voltage drops to a very low value or zero, there can be no raster. With focus voltage at about 50 percent of normal, you probably can see fuzzy blobs of color-the highlights of the picture-floating around the screen. But be sure high voltage is up; if it's not, you can't do a thing with the focus stage. If the high voltage is only half of normal and the hori- zontal output tube overheats, a selenium focus rectifier may be shorted. Also check for a shorted pulse-coupling capacitor (diagram B). Shorted turns in the focus trans- former can overload and destroy the flyback. Cathode current in the horizontal output tube is a good clue. Measure it. If it is high, yet the circuit tries to pro- duce high voltage, disconnect the focus transformer. If it's shorted, disconnecting it returns the cathode current and high voltage almost to normal. If high voltage is normal and cathode current within reasonable limits, yet focus voltage is very low or zero, suspect an open focus rectifier. The solid-state type rarely open. Usually, they partially short and overload the fly- back and output tube. A change in value of a high-resistance bleeder can raise or lower focus voltage. If a plastic-encased one goes bad, use an exact duplicate. Check potentiometers. The kind in diagram A is espe- cially critical. Never spray it to clean it. If contact gets poor, or the element starts arcing to ground, replace the -it pot. Use a thick sheet of polyethylene film between the control and the mounting increases the insulation path. It's best to replace pots in divider circuits, too, if they begin to get scratchy. Cleaning rarely lasts more than a few days (or hours). They can also change value, which upsets the voltage. If sets with voltage multipliers (diagram D), any high- voltage trouble also affects focus voltage. If an individual rectifier in one of these goes bad, it's a good idea to replace the whole "board- full" of rectifiers. All of them have prob- ably been subjected to overload. R-E WAVEFORMS AS GUIDES WF 1 Normal Unknown V p-p This waveform is sample picked up by holding scope probe near focus transformer (diagram B). It has little practical value for diagnosis. It varies in shape and peak-to -peak amplitude as the core of the focus transformer is adjusted. The changes verify that the core is affecting coupling in the transformer, but the changing value of dc voltage at the rectifier cathode tells you the same thing. Changing parts values elsewhere in the circuit have little or no effect on the waveform. See DC Voltages As Guides for better help in diagnosis. NEW BOOKS LOGIC CIRCUITS, by N. M. Morris. McGraw Hill Book Co., 330 West 42 St., New York, N.Y. 10036. 199 pages, 6 x 9 in. $13.50. A general guide to design and use of logic devices and systems with chapter review questions for self- study. Chapters describe numbering systems and codes, arithmetic processes, the flip -flop, counting systems and hardware. Advantages of Karnaugh map method are described. 48 MOTOROLA COLOR TV SERVICE MANUAL, by Forest H. Belt. Tab Books, Blue Ridge Summit, Pa. 17214. 160 pp., 81/2 x 11 ". Softcover, $4.95. Covers all models using TS- 907-TS924 chassis. First chapters are on monochrome purity, gray-scale tracking, static and dynamic convergence adjustments, as well as tuner repair. Remaining chapters are devoted to analysis of each chassis. HANDBOOK OF PRACTICAL ELECTRONIC TESTS AND MEASUREMENTS, by John D. Lenk. Prentice -Hall, Inc., Englewood Cliffs, N.J. 07632. 302 pages, 61/4 x 9% in. $15. Guide to most practical electronic test and measurement procedures encountered by electronic technicians. Covers component tests and quantity measurements. Generally, a quick procedure with simple equipment is described along with a detailed lab procedure. R -E RADIO -ELECTRONICS www.americanradiohistory.com Constant-Speed Motors for Tape Recorders by AL WILLIAMS'" THIS SUMMER, IF YOU LIVE IN A REA- sonably large city, you found that at various times many of your appli- ances-from toasters to refrigerators, to blenders -were working at some- thing less than maximum efficiency. Worse, some of your high -fidelity equipment did not work up to standard. It wasn't the fault of the appliances or components. The plain fact is that there were serious voltage drops at certain times of the day. Actually, voltage under the best conditions may vary considerably from the standard 115 to 120 -volts supposedly delivered to your household outlets. It's not just a summer problem, when air conditioners create a tremendous demand on available power. It can happen almost anywhere, anytime. A case in point is a busy ski area in Southern Vermont. During the evening, with every lodge filled to capacity, there is a definite loss in light levels compared with other times of the year. A serious voltage drop can affect tape recording quality. The problem can be as sticky for the amateur home recordist as for the professional working on location. Let's take a look at specifics and the part that the motor drive -and hysteresis synchronous motors -can do to help the situation. The fundamental task of a transport system is the smooth, constant movement of recording tape through the tape head contact area. Achieving and maintaining this movement under varying ambient conditions is the transport designer's challenge. Some of the annoying results of inadequate transport design include change in key or pitch of recorded audio information and random fluctuations detectable as wow and flutter. These problems can occur due to ac input power line variations as well as loading changes within the transport system. The drive motor is the prime mover in the transport system. All tape speed deviations, whether stationary or time varying ones, can ultimately be referred back to the drive motor. Therefore, the essential specification for a tape transport drive mo- *Chief Engineer Concord Electronics Corp. OCTOBER 1970 tor is constant speed. In terms of practical design the linkage between drive motor and the rest of the tape transport system will typically involve belts or friction wheels. And in order to keep a reserve of momentum at the point of contact between the tape and drive system (the capstan), inertia is supplied with a flywheel attached to the capstan shaft directly. The flywheel removes short term disturbances in the transport motion, but its average angular velocity must be maintained with the drive motor. The types of motors or motor systems which might be selected by the designer include dc motors with mechanical or electronic regulation; ac induction motors; and ac synchronous motors. Dc motors with governors are widely used in and generally restricted to low cost portable battery operated recorders, but have been used, occasionally, in component class recorders where battery supplies are not used. The disadvantages of the dc system include brush and contact noise if mechanical regulation is employed, the need to supply dc, and usually some additional circuitry such as amplifiers and /or filters. Remote control of motor speed is a possible but very minor advantage of the dc system. Ac induction motors of single- or two -phase design are often found in a variety of tape recorders primarily because of their simplicity and low cost. In the single -phase induction motor the rotor speed is highly dependent on the ac source voltage and will change significantly with minor changes in source voltage. A two -phase induction motor may be coupled with a detector and servo amplifier to provide motor speed control. This approach is complicated. costly, and commonly relegated to control functions such as head motor speed in video recorders. Ac synchronous motors represent a class of motors that are selfcorrecting relative to rotor speed and consequently deserve first consideration in tape transport design especially for the component type recorder. A "self- correcting" mechanism implies some form of servo system which will oppose fluctuations in both input power and output load in order to maintain some predetermined characteristic in the overall system output. A servo system is comprised of a detector and feedback mechanism usually incorporating amplification. Comparative transport perform- ance has proven the superiority of the hysteresis synchronous motor particu- larly in large cities where ac voltage fluctuations are extreme during high demand periods of the day and in heavy industrial locations where ex- treme fluctuations may be more frequent if not more severe. While the amplitude of the ac power undergoes large changes, the frequency (60 Hz standard) remains closely controlled. Such circumstances clearly suggest preference of the synchronous motor over ordinary induction motors in se- lecting a tape transport drive. The transport speed of Concord MK series decks has been controlled to within 0.7% for ac power fluctuation of between 100 and 128 Vac and within 1.0% over an 80 to 140 Vac range, surpassing the dynamic range of either ac induction or dc servo-con- trolled machines tested under identical circumstances. The hysteresis synchronous mo- tor takes special advantage of the phe- nomenon of hysteresis for detection of an error signal and generation of a correction signal. Hysteresis as related to the synchronous motor means the lag in magnetic effect which in the synchronous motor is used to store and compare the phase of the angular velocity of the rotor with the electrical phase of the ac source, some of which flows in the stator windings. The synchronous motor then per- forms magnetic amplification of the correction signal that subsequently alters the angular velocity of the rotor just enough to eliminate the error signal. This process is a dynamic one taking place on a continuous basis. The result is a phase lock between the frequency of the ac source and the frequency (rpm) of the rotor. Once locked in phase the motor speed is highly dependent on the frequency of the ac source and remarkably independent of the voltage level of the ac source. Phase lock will be lost only when the ratio of motor load to input power is excessive. In addition to the basic synchronous motor windings, others are included which serve two important purposes, that of self -starting and dynamic damping in case of large sudden changes in rotor load. Hence, the hysteresis synchronous motor is a self- contained closed loop phase lock servo system that can fur- nish constant speed over a wide range of power levels. R -E 49 www.americanradiohistory.com Now To The PUT or complementary SCR is new solid -state device. Here is how it works and how to use it. 4 LAYER SCR SCS PUT DIODE Putter With The Put by R. W. FOX About three years ago, the General Electric Company introduced the fourth member of the pnpn structure. This device has been called both a Programmable Unijunction Transistor (PUT), since it may be used in place of the unijunction transitor, and a complementary SCR. The former name is to show a major use of the device while the latter is a more descriptive name. General Electric has at present two devices on the market, the C13 Complementary SCR and the D13T PUT. These two devices are specified for their respective tasks, but to a degree may be interchanged. This article is devoted mainly to the D13T PUT. Several of the applications and much of the theory can apply equally to both devices. Included are theory, UJT replacement, switching circuits and many examples of their use. Theory of the PUT In Fig. 1, the equivalent circuit shows the two transistor analogue of a pnpn structure. For an SCR, the gate is the base of the npn transistor, but for the PUT the gate is the base of the pnp transistor. This is the differ- ence between a PUT (and /or a com- plementary SCR) and an SCR. The theory follows normal thyristor theory for turn -on, turn -off and latching, etc. o K Fig. 1- PROGRAMMABLE UNIJUNC- TION transistor and its equivalent circuit. The device is turned on by making the gate negative with respect to the anode by a little more than the diode offset voltage so that enough anode current exists through the first pn junction (i.e., the anode -anode gate junction) to cause regeneration to oc50 cur. This current can be considered base current for the pnp transistor. The current required to trigger is typically on the order of a microampere. The current at which regeneration takes place is defined as the peak -point current (lp). As the regeneration causes the anode -cathode voltage to collapse the device switches to the conducting state. The time for device turn -on is about 50 to 100 nanoseconds. (This turn -on, it should be noted, is an order of magnitude faster than the conventional unijunction transistor.) This results in a steep pulse for high di /dt SCR trigger ap- plications. The device is now in the on-state, and in this region there are two parameters of great interest. I These parameters (shown in Fig. 2) are Ir or valley current and or I --i -- IP V V Vp Y Fig. 2- ANODE- CATHODE CHARACTER - 1ST ICS based on the I,: and I parameters. holding current. Valley current is the point at which the PUT starts out of saturation, however, because of the beta shifts in the two transistors, the device will remain in conduction until the holding current is reached. The device at this point returns to a nonconducting state. The PUT in relaxation oscillators Figure 3 shows a typical PUT relaxation oscillator. This circuit has two allowable states. State 1 will be for the PUT in the off or non -conducting state and state 2 will be for the PUT in the on-state. First let's analyze the steady state conditions. Assume that the PUT is in state 1. After sufficient time - the capacitor will be charged to (VAA RAIe,.), where IcL is capacitor - - leakage current. The anode-cathode voltage would be (VAA RAIe,. where IL is the cathode leakage current VGG Fig. 3 -A PUT RELAXATION OS- CILLATOR. Like most circuits of this type, the active element is either on or off. - (which usually may be neglected). The voltage would be (Voo R,;Io0), where Ia° would be the gate current with device off. (At room temperature I,;0 will be less than 10 nanoamperes). If this state is allowed then: - VAA RA (IL + IeL) - < V00 R0Ia0 + VT Eq.1 Where VT is the gate offset voltage to trigger. If this equation is satisfied then this state is a permissible state, and the output voltage (Vo) is I,.RL. Assuming that IL, Ie,. and I,;,, are negligible, Equation I reduces to: VAA Ç (V,:n + VT) Eq. 2 Equation 2 points out vividly that as long as the anode supply voltage is - less than the effective gate source volt- age (VuE Vap VT) the PUT will remain non-conducting. If the PUT is initially in state 2, then the following relationships will hold: V, ;0 = (Ra + RL) Io + RLIAR Eq. 3 = + VAA (RA RL) Ia -}- RLIo Eq. 4 Vo =R,,(IG-}-IAA) Eq.5 Where IA,; iS anode -cathode current and V, is the forward voltage drop. If IAE > In Eq. 6 then the PUT will remain in conduc- tion. If V,;. is applied to the circuit of Fig. 3 and then VAA is applied, capacitor C will charge exponentially toward VAA. If Equation 2 is satisfied then the PUT RADIO -ELECTRONICS www.americanradiohistory.com does not turn -on. If, on the other hand > VAA (VGG VT) then it may be possible for the PUT to turn on. As the capacitor charges the current through RA decays exponentially. When VG = (VGG -1- VT) the current through - - RA is: IA (VAA Vc) /RA Eq. 7 It is at this point the PUT will trigger, if at all. For the PUT to be triggered IA I Eq. 8 For if IA is less than I,. then regenera- tion cannot occur and the device re- mains in State 1. If regeneration occurs then the anode -cathode voltage collapses and VG appears across R,,. Voltage VG will now follow Vc on an ex- ponential decay less the forward drop of the PUT to one of two end points. The first is the case where equation 6 holds; the second where it does not. It can be seen, if the capacitor has been discharged, and Equation 6 still holds, then, as a consequence the PUT will remain conducting. In the other case, as the capacitor discharges, there will be a point in the disoharge at which the anode current has dropped below the holding current. At this point the PUT returns to State 1 and the capacitor is recharged through RA. This is the free-running relaxation oscillator. PUT fudge factors In the above discussion, I,,, I,, VT and VGG were assumed. The parameters, though, are not just single numbers that are merely plugged into equations. Each of these may be varied 1- over a considerable range. Factor No. Stand -Off Ratio (n) VAA. B2 VBB ir VA A rlVBB Fig. 4 -a -A UJT b RELAXATION OS- CILLATOR and (b) a comparable PUT circuit. OCTOBER 1970 In the above example two power supplies were used for the relaxation oscillator. In a conventional unijunction circuit (Fig. 4-a) only one supply is used and the peak capacitor voltage at turn-on is expressed as a function of the inter base voltage (Vß). How- ever, between UJT's of the same type this function, the stand -off ratio (n), varies by 10 to 20 %. With the PUT each and every peak -point will be essentially the same and the designer may pick his peak -point over the range from 0.1 to 0.9. The stand -off ratio is merely the ratio of resistors in divider R1 -R2 in Fig. 4 -b. Thus, for the PUT, the stand -off ratio is: n =R,/(R,+R2) Eq.9 Factor No. 2-Peak Point Current (I,.) Peak-point current is a function of gate source impedance and temperature, one is an advantage but one a disadvantage. As gate source impedance and temperature are raised the peak -point current decreases. Temperature compensation will be discussed in a later section. Figure 5 -a and 5 -b show 10 4 z w 1 u z_ o1 4 wa 0.01 -75 -50 -25 0 25 50 75 100 AMBIENT TEMPERATURE- °C a ---_ -v - 1K ---.."--,- - 10K` ._-....- ---.-- K "OI MOEKG...... - : IOKt IOOK -^ERG= IMEG -01-031T3T21 =-- RG VSs 001 I IO 15 20 - VS SUPPLY VOLTS b Fig. 5 -PEAK -POINT CURRENT is a function of gate source impedance and of temperature. Chart (a) plots peak-point current against temperature and chart (b) against supply voltage (V) for different values of gate source impedance RG. the typical variations of peak-point current with changes in temperature and Vs (gate supply volts) for different 3- values of gate series resistance (R0). Factor No. Valley Current (Ir) Valley current can be varied the same way the peak-point current is -'-r-is-s--+- 100 -- IK - IIOK K----. =1óóK - -IMEG -I00K -°RGIMEG - RGG --DIDS13TT2I VS - 10 15 VS SUPPLY VOLTS 20 1000 _ RG I0K VSIOVOLTS RG I00K RG IMEG -75 -50 -25 0 25 50 75 100 AMBIENT TEMPERATURE-°C Fig. 6--VALLEY CURRENT character- istics, for given with VG (chart a) gate impedance, varies and temperature (b). varied. Figures 6-a and 6-b show this variation. Factor No. 4-Offset Voltage (VT) Since the PUT, like most thyristors, is current triggered, the offset voltage is a function of gate source impedance. In reality this offset is due to the diode voltage drop between anode and gate, hence it is a function of temperature. Figure 7 shows the 3 I MEG Vs .10 VOLTS -75 -50 -25 0 25 50 75 100 AMBIENT TEMPERATURE-°C Fig. 7- TRIGGER OFFSET VOLTAGE for a programmable uni junction transistor varies with ambient temperature level and with the series impedance at the gate. typical variation of VT with gate source impedance and temperature. Replacing UJT's with PUT's In many cases a designer will wish to replace a UJT with a PUT to obtain a cost or performance advantage. Using the PUT (D13T) in a cir- 51 www.americanradiohistory.com cuit in place of an unijunction is easily understood. Figure 8 -a shows a basic unijunction circuit. Figure 9 -a shows the identically same circuit except the unijunction transistor is replaced by the D13T plus the resistors R1 and R2. Comparing the equivalent circuits of Figs. 8 -b and 9 -b, it can be seen that both circuits have a diode connected to a voltage divider. When this diode is forward biased in the unijunction transistor, R1 becomes strongly modulated to a lower resistance value. This action generates a negative resistance characteristic between the emitter (E) and base one (BI). For D13T, resistors R1 and R2 control the voltage at which the anode gate diode becomes forward biased. After the diode conducts, the regeneration inherent in a thyristor causes the PUT to switch on. This generates a negative resistance characteristic from anode to cathode simulating the modulation of R, in the conventional uni- junction. Resistors Rß_ and R,;, (Figure 8 -a) are generally unnecessary when the DI3T replaces a conventional UJT. This is illustrated in Fig. 9 -c. Resistor R,,, is often used to bypass the interbase current of the unijunction which would otherwise trigger the SCR. Since R1 in the case of the PUT (DI3T), can be returned directly to ground there is only the peak-point current of the PUT (about litA) to bypass. Resistor R,,, is used for temperature compensation and for limiting the dissipation in the UJT during capacitor discharge. Since R2 (Fig. 9) is not modulated, R,,., can be absorbed into it. The result is the circuit of Fig. 9 -b which contains the same number of components as the UJT circuit but at a lower cost and with better performance. Resistors R 1 and R2 have been removed from the pulse circuit, there is no reason why they cannot be changed in impedance to change the peak -point and valley currents as required by the application. Applications of the PUT The PUT with its flexibility can be tailored to fit many places where a UJT would not be acceptable; but before proceeding to some examples of this type of circuitry, there is a need to examine some final UJT applications of the PUT. It was noted above and shown in Fig. 5 and 6 that peak and valley current were functions of gate source impedance. Since they both decrease with increase in gate source impedance there could be a problem if we wish to vary them independently. Figure 10 shows some variations on the gate circuitry. 52 In normal UJT circuitry the interbase resistance is normally about 10,000 ohms, with the PUT impedance level as a design factor. Figure 10 -a shows a high- impedance divider which gives low Ip and low Io. If you want characteristics closer to the UJT's, use the circuit in Fig. 10 -b. Remembering that at the peak -point the anode (point E) of the PUT (DI3T) is above the gate potential by VT. Thus the diode is reversed biased and the gate source impedance is high (1megohm in this case). But at the valley-point the gate is near cathode potential (point B1), so that the diode is forward biased and the gate source impedance is low (about 1000 ohms). + E B2 Re RB2 y UJT' B2 R2 Res .RI +R2 RI SCR RI .9 RI +R2 RBI 131 a b VEB) C Fig. 8-a -A TYPICAL UNIJUNCTION driving an SCR. b -UJT equivalent cir- cuit and (c) negative- resistance characteristic. 82 81 o b C c- Fig. 9-HOW circuit in Fig. A 8 PUT REPLACES UJT in -a. b -UJT equivalent cir- cuit using programmable unijunction. The simplified PUT version of Fig. 8-a. "82 "82" o DI3T b NB2/ C Fig. 10-TYPICAL UNIJUNCTION circuit configurations. a -For low I and low b -Use paralleled diode and resistor for low 1,. -high and (c) for low I . and high 1 with temperature compensation. -A Fig. 11 ONE HOUR TIMER using a pair of PUT's. The first does the timing; the second one triggers the load circuit. This circuit has a low Ip and relatively high I.. Figure 10-c shows a similar diode network that provides temperature compensation of VT(VAG). When the peak -point is approached, the trigger - - point is when (VE VT) = (V,0 V1,) Eq. 10 where VW; is the effective gate source voltage; VE is the emitter of the V equivalent UJT and is the diode forward drop. Equation 10 shows that temperature compensation is obtained when the diode's temperature co- efficient is the same as VT. In Fig. 11 there is shown a one-hour timer using a single D13T2 PUT for timing and to develop a trigger pulse for the D13T1 at the end of the delay. (continued next mònth) RADIO -ELECTRONICS www.americanradiohistory.com TAPE RECORDING by DAVID K. KIRK PERHAPS IT'S BECAUSE NOBODY HAS yet decided what magnetic fields really are. Maybe the reason is simply the comparative youth of the system. The fact remains that magnetic tape recording is both the most fascinating and the most mystifying aspect of modern audio. If you find this hard to swallow, try your hand at these. The upper limit of recorded frequency range is set by the length of the record head gap. False. At high frequencies, only one side of the record head gap needs to be operative to place a related signal pattern on the tape. Most audio recorders have a record bandwidth of well over 40 kHz at 71/2 ips and record their own high frequency bias. Pull the tape along at 1 ips and you will hear it. The effect can be quite annoying to anyone trying to edit a 15 ips tape, where it is necessary to rock the tape slowly back and forwards across the playback head. The main factor limiting overall bandwidth is the replay head gap, where the "trailing edge" recording effect does not apply. Storing tape without rewinding reduces print- through. True but how many followers of this common studio practice realize why? The general theory, and it's wrong, is that post -echo rather than pre-echo is printed when the tape is stored without rewinding and post -echo is less audible, being drowned in the decay of the transient that caused it. Actually, print- through travels in both directions by equal degrees, causing equal amounts of preand post -echo. Then why does storage without rewinding work? Because print through is largely a temporary effect that disappears after a few seconds out of contact with the responsible field. Storing tape before rewinding means that a program must be rewound a few minutes before playback. This act alone gives the print through time to decay. On some tape transports, the time lag between the tape leaving the feed reel and reaching the play head is great enough for the (continued on page 58) OCTOBER 1970 facts and fallacies You probably don't know all the answers, but if you get all of these right, class yourself an expert! www.americanradiohistory.com RhiEgEhL-q-TuOal-itRyEEpLrofTeEsAsiConaAl--7t0y1p0e for home use. is typical of equipment 53 Second in a series... Ctinhaeenslyeeocputrroosnboillcevsem?s They're a cinch after you've taken RCA Institutes' new communications electronics program. It includes new preparation for the FCC license plus the assurance of your money back if you fail to get it. This one is quite elementary. This one is more advanced. - In this door bell circuit, which kind of transformer is T, step -up or step-down? Note: if you had completed only the first lesson of any of the RCA Institutes Home Study programs, you'd easily solve this problem. lWS uMOp-datS :sJaMSUy 54 ' 20 ' 2,0 ' 10 What is the total capacitance in the above circuit? Note: you'd know the solution to the problem if you'd taken only the first two lessons in RCA's new Communications Electronics Program. These are the lessons that prepare you step -bystep for an FCC License. This license is a requirement for servicing all types of transmitting equipment and can help open doors to jobs commanding high income in communications, radio and broadcasting, aerospace, industrial automation and many others. - For a rewarding career with good pay, take that first step now. Send for complete information mail the attached card. RADIO -ELECTRONICS RCA Institutes Autotext learning method makes problem -solving easier... gets you started faster towards a good-paying career in electronics Are you just a beginner with an interest in electronics? Or, are you already making a living in electronics, and want to brush -up or expand your knowledge? In either case, RCA has the training you need. And Autotext, RCA Institutes' own method of Home Training will help you learn more quickly and with less effort. Wide Range of Courses Select from a wide range of courses. Pick the one that suits you best and check it off on the attached card. Courses are available for beginners and advanced technicians. Electronics Fundamentals Black & White Television Servicing (Transistorized TV Kit Available) Color Television Servicing (Color TV Kit Available) FCC License Preparation Automatic Controls Automation Electronics Industrial Electronics Nuclear Instrumentation Electronics Drafting Computer Programming Plus these new up-to- the-minute courses Semiconductor Electronics Digital Electronics Solid State Electronics Build and keep this valuable oscilloscope. Communications Electronics Prepare for good paying positions in fields like these Television Servicing Telecommunications Mobile Communications CATV Broadcasting Marine Communications Nuclear Instrumentation Industrial Electronics Automation Computer Programming Solid State Electronics Drafting In the new program on Solid State Electronics you will study the effects of temperature and leakage characteristics of transistors. ncn OCTOBER 1970 Variety of Kits -Yours to Keep A variety of RCA Institutes engineered kits are included in your program of study. Each kit is yours to keep when you've completed the course. Among the kits you construct and keep is a working signal generator, a multimeter, a fully transistorized breadboard superheterodyne AM receiver, and the all- important oscilloscope. These 4 kits are at no extra cost. Compare this selection with other home study schools. Two Convenient Payment Plans Pay for lessons as you order them. No contract obligating you to continue the course. Or, you can take advantage of RCA's convenient monthly payment plan. No interest charges! Classroom Training Also Available RCA Institutes operates one of the largest technical schools of its kind. Day and evening classes. No previous training is required. Preparatory courses are available. Classes start four times a year. Job Placement Service, Too! Companies like Bell Telephone Labs, GE, Honeywell, IBM, RCA, Westinghouse, Xerox, and major radio and TV networks have regularly employed graduates through RCA Institutes' own placement service. All RCA Institutes courses and programs are approved for veterans under the new G.I. Bill. Send Attached Postage Paid Card Today. Check Home Study or Classroom Training. rAccredited Member National Home Study Council. -1 IF REPLY CARD IS DETACHED, SEND THIS COUPON RCA Institutes Inc. Home Study Dept. 758 -010 -0 320 West 31 Street New York, N.Y. 10001 Please send me FREE illustrated career catalog. Name Address City L (please print) State Ago Zip J 57 www.americanradiohistory.com ( continued from page 53) print to fall below audibility; so no need for preplayback winding. Magnetic tape wears out. False. Run a brand new tape through a recorder with clean heads and measure the frequency response. Rewind, clean the heads once more, and mea- sure again. The 7-20 -kHz response should be at least 2 dB up on the virgin figures. Far from wearing out, professional and high -quality tape actually improves with age, the oxide coating smoothing out to a level, dustfree surface. By contrast, most new tapes are covered in a fine powder of loose excess oxide. This clogs the record and play heads, causing high frequency attenuation. A brand new tape should always be fast-wound a few times before serious use. The best way to dub a tape is backwards. This one is true, strange though it may seem, and is applied by at least one major tape recording manufacturer. Run any recording backwards and you will notice an apparent lack of high frequencies that makes you reach for the treble boost. The reason is that the reversed tape is devoid of sudden transients; our ears are climbing relatively slowly up what would naturally be the decay. The sudden cutoff at the "end" of each transient has little impact on our ears. Under normal conditions, the ampli- VARIABLE NOISE FILTER is featured in Ampex AX -300. Other versions offer automatic threading too. fiers would be prone to "ringing" on the leading edge of strong transients. Reversed, the only sudden change they have to make is in downward level. Residual head magnetism builds up over several hours. False, or at best only half true. The major cause of residual head magnetism is dc from the tape amplifier reaching the record and /or play heads. This occurs to some extent in almost all recorders, particularly where a high -value capacitor is in circuit close to the heads. A degaussed head can become remagnetized within minutes, depending on the circuit design, input load and operational switching sequence. A 30 Hz-20 kHz +3 dB fre- quency response gives better quality than 30 Hz-12 kHz +3 dB. This may be true of amplifiers but with tape equipment is a very false assumption indeed. When a manufacturer or service engineer sets the bias current of a recorder, he usually goes for wide frequency range simply because the customer, reared on specifications, ex- pects it. Most studios, however, rightly set the bias at a higher level in order to secure maximum signal -to-noise ratio and minimum distortion for a particular brand or (tape is very variable) individual reel of tape. Studios appreciate that lifting the high-frequency response to extremes inevitably brings in an extra octave of noise, both from the tape and from the preemphasis circuits. It's no good throwing figures at the public. A dealer who wants to guarantee himself regular customers should let them hear an A-B comparison of two machines, one biased for maximum frequency range at 3% distortion, the other for maximum signal-to-noise ratio at around 1.5% distortion. Most people will go for the latter because most people don't like hiss. [A few socalled non -professional recorders (e.g., Tandberg's model 6000) offer extended frequency response with excellent signal -to-noise ratios and low distortion. Also, Dolby noise reducers RECORD AMPLIFIERS ARE STACKED below the tape deck in the Roberts model 771X. (Advent, Harmon -Kardon) now per- mit extended response without tape hiss.- EDITORS] Quarter -track systems produce more hiss than t/-track. False. When you switch from a 3/4-track playback head on a stereo recorder to a I/2- track head, the hiss will go up, not down as a lot of people seem to ex- pect. The 1/2-track head theoretically produces 3 dB more hiss than the 3/4- track, so an A -B test on background noise alone will show 1/2-track to be the "inferior" system. The important fact is that 1/2 -track produces a full 6 dB increase in signal level and, when the 3 dB hiss is allowed for, this makes a 3 dB improvement in signalto -noise ratio. It is the latter 3 dB that counts. Finally a question the reader might like to puzzle over. The answer requires nothing more than a basic understanding of equalization. When asked to make copies of a 33/4 ips master on 15 ips speed-to-speed equipment for later playback at 33/4 ips, for what speed do you set (a) the equalization of the playback machine and (b) the preemphasis of the recorder? R -E COLOR TV ANTENNA INSTALLER'S GUIDE This month Section II of your Radio -Electronics Reference Manual continues to grow. We present the final part of an article on TV antenna installation. If you wish, you can purchase a special hardcover binder to keep your Reference Manual pages together. It has a dark blue fabric cover and is gold- stamped Radio -Electronics Reference Manual. The cost is $1.00 postpaid. Order from N. Estrada, 17 Slate Lane, Central Islip, L. I., N. Y. 11722. 58 RADIO -ELECTRONICS www.americanradiohistory.com á 9E 3 ó E °,N - `r-° a^o N m rm m m tp m U ? Z2 wZ U t/1 J > Z J J J Z O ci 2 p 2 . N Q N Q Q H(2) 2 Q 2 O _ U >--iu,>, Q- J;} Q Cr 3¢ m f Q U Ö U. Ú U Q W I _- Q Q 22 2 - _ W co m 2 2 O 2 á H 2 IZ_ tn 3 aZ--r Ztu aZW L- O O á W.-o O,f 0 NLc-) M OMO M v(p t _ O t1¡ _ cri O rn d N N,n d t7 D c L Ó 00 .... Cr-+ N 3 a-W=OoO.. o=" OL O Ó. 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" (a o>=, v- - +O+ V) V) y a) C 'Ç Ñ R bC A C 7 Q m= 0 .L- Ú(II E ;-< O ('7 a>) ..- > L N° L (o fEß _(ß (n a) C ' >.0 ° +Q- 4) a) a) (6a N 4-, 0 v) C p(ß Ç 1-- co (O U+--' bCA E +, cco O U a) v) = N Q O F- fß U a) E '_ C ß (ß co sr' p ++ a) (ß O L m a) +°, (6 C E a) V) >. ß L i(bX> 3.c v) w -o c L L C(ß O 3 '°-(n° +O., a) Q] E (n O O (ß C OU -° as C a) L ++ + c C .° ' a) -°api b°A °U N m O C(o Ç + fl (n c L L L Ú O a) ++ cc-i O Ñ =o (n aci =C+Jas >T bA v- O UÌ (ß CO E+°- a) M ad 7) ai 4] L LEÚa)OaL) L L L 4) (6 (O U O C co V= ) O M +- H >"..E LE v) www.americanradiohistory.com IN GUT ULTIPLEX GENERATOR IN R OUT iluihi Ellt stereo multiplex COMPOSITE MODULATION R GNG AUDIO 'No The stereo generator described here is designed for low cost and simplicity. It compares favorably to commercial units in stereo performance, but does not have self- contained audio signals or i.f. test signals. Only a 1 -kHz signal and -a general -purpose scope are required for aligning this generator. An FM receiver should also be available. The generator provides over 30 dB stereo separation between 300 and 20,000 Hz. Total parts cost is around $50, but many parts are common and can be found in your spare parts box. This unit does have an rf output to check an entire receiver's performance without an external rf generator. The high-frequency oscillator works at 106 ±2 MHz and is frequency modulated by a variable- capacitance diode. A regulated power supply is incorporated and gives exceptional rf stability. Theory of operation A basic understanding of FM stereo transmission will aid the user in understanding the generator operation and design theory. The FCC controls the method of stereo transmission. The base band spectrum is shown in Fig. 1. The RELATIVE AMPLITUDE SUPPRESSED STEREO SUBCARRIER 80 PILOT SUBCARRIER L -R SIDEBANDS MAX LrR SIDEBAND SCA (WHEN USED) /, 15 19 23 38 53 59 67 75 MODULATION FREQUENCY- kHz Fig. 1-FREQUENCY frequency modulated SPECTRUM in a stereo broadcast. monaural information or average left plus right (L-1-R) signal is contained in the 0 to 15 kHz useful audio range. The L -R information required for stereo demodulation is transmitted as an amplitude modulated 38 -kHz suppressed -subcarrier signal. This will result in frequency components ±15 kHz around 38 kHz, or 23 to 53 kHz. The 38 -kHz subcarrier must be reinserted in the correct phase at the receiver to obtain the complete stereo information. To do this, a low-level 19-kHz pilot signal is transmitted which has a definite phase relationship with the orginal 38 -kHz subcarrier at the transmitter. This pilot OCTOBER 1970 1 KHZ generator MONITOR M ,a Z by AL FRANSON With the popularity of FM stereo receivers, test equipment to align these sets is a must for service technicians and anyone interested in building FM receivers. To get good stereo separation from a receiver, a multiplex generator is much better than adjusting the set by "ear." phasing is one of the most important properties of the transmitted composite signal and is discussed in greater detail in the section on alignment procedures. A few FM stations also transmit a 67kHz storecast subcarrier. This signal is a frequency modulated subcarrier occupying the spectrum from 59 to 75 kHz. This subcarrier was not included in this generator since it has nothing to do with aligning stereo separation of a receiver. The composite baseband signal shown in Fig. 1 now frequency modulates the rf carrier between 88 and 108 MHz at a maximum deviation of ±75 kHz peak. Broadcast stations use pre- emphasis of the audio inputs which increases the level of audio frequencies above 2 kHz. This makes a de-emphasis necessary in stereo FM receivers to restore correct frequency response. This pre- emphasis at the transmitter occurs before multiplexing. In other words, the subcarriers previously mentioned are not pre-emphasized. This makes it unnecessary to include pre-emphasis in a stereo generator which is used for alignment purposes. If pre -emphasis is desired, it can be applied to the audio input signals before they are fed to this generator. Circuit description Transistor Q1 in Fig. 2 operates as a 19-kHz oscillator with the exact frequency of oscillation determined by the twin-T feedback network. The twin-T network makes a very stable oscillator once R2 is adjusted for 19 kHz. The 11 -volt peak-to -peak output of the oscillator (Fig. 3) is fed to a phase -shift network through Fig. 3 -PILOT SUBCARRIER signal gen- erated in 19 -kHz Twin -T oscillator Ql. buffer amplifier Q2. The phase-shifter is also isolated from the summer through buffer amplifier Q3. The phase-shifter provides a means of correcting phase relationship between the 19-kHz pilot and the 38kHz subcarrier. The range of phase shift available is about 120 °. A maximum phase shift variation of 90° is necessary. Transistor Q4 is the doubler amplifier which delivers two equal but opposite polarity signals to diodes D1 and D2 which full -wave rectify the 19 -kHz signal. Germanium diodes are used for highest rectification efficiency. This distorted waveform (shown in Fig. 4) is 1,1: (\An nnirli Fig. 4- DISTORTED SIGNAL results when 19 -kHz subcarrier is rectified. passed through an active bandpass filter consisting of Q5, Q6, and Q11. This is a twin -T filter which has excellent selectivity. The filter output is shown in Fig. 5. 1 1 II il !III 1 Ait\j VAPA Fig. 5 -THE STEREO SUBCARRIER is cl p by sharp 38-kHz Twin -T filter. The two audio inputs representing left and right channels must be conditioned to give L+R and L -R signals for proper stero transmission. The left and right inputs are fed to the summer, Q10, which is a feedback amplifier that provides greater than 20 dB isolation between L and R inputs. The actual isolation is partially determined by the generator internal impedances used to fed the L and R signal inputs. Source impedances below 100 ohms should be used to give greater than 40 dB isolation. Transistor Q7 is operated as an in- verter to give -R at its output. This is summed with L by Q8 to give R-L at its output. R31 and R22 must be adjusted to give proper stereo separation. The R-L signal is used to modulate the 38 -kHz subcarrier delivered by Q11. This is done with a ring modulator with 63 www.americanradiohistory.com 19kHz OSC. R3 R4 6.8K 6.8K C3 .003T OK R5 R6 C4 56K 5bK 01 222 SUMMER 00_ MPS2923 PHASE SHIFTER MPS2923 R43 R44 R45 Q3 C I0K 19kHz R57,5111 J1,MONITOR 120V R58,39011 C2A30 ,v 10K 50K R42 C21 C22 560L1 A043820pF R41 82011 SyF23 R46 10K PILOT LEVEL R47 10K C24 .0 R48 1, ?2y0 R56 .-.IOOK R55 3.9K IC-I MC 1531G* MPS918 ISäiC36 A341_ T - 6.2V - 15PF s 100MHz VCO C38 (13. pF R71 012 47K D9,IN5234 +6V R=59C33 J 5K- SyFi R67 22X. 337 C39 TpF OOI R68 470 COMPOSITE MODULATION 9 22K C40 IOO pF DIO IN5140 3V £R73 IK R7 I0K RB +1Ç5,5,6yF T IK C20,.1 R54 IOK 1 MPS2923(2) RII RIO 47° C6,.1 IN276(2) R37 15K 56K R35 C19 MPS2923 R12 6.8K 5.6K .01 RI3 47011 C7,.I R14 RI5 2K 12K R36 5.6K 4.71 /,KR5- R39 2.7K 38kHz FILTER C25,.001 C26001 06 tR50 68K R49 4.7K s 10K R5K52 _ = T T CV S- -L-C28"' .00 .001 R16,22Kf RNIpGIH¡TT C8 C9 +2011F J5 R20 RI7 IS1 K tt10K - = YR21 R18 CIO IK 301+F MPS2923 1IK29 1 R19 CÌI R22 680 I00yf 10K J6 IK ° ± 47KS 03 R27 560 J7 vN 00 00jF 2923 I00 F CI ;.4, CI8,5LyF R31 10K R 76 \`/ MPS29 -23_ti-\¡ 1 OB OKy IK R30 1.5K + 09 T 06 20yF MPS2923 C15 pF pOUT SI IN LEFT INPUT R23 R25 47K_ OIÓ R 28 +.1.. C14 1.5K T 20pF * SEE TEXT Fig. 2 011 TP-1 I R53 33011 P64 33011 117 VAC iR66 C41 IN3064 ( 4) BALANCED MODULATOR 1: TI C T ` 1 R60 D4 R61 56011 R63 560n C.TT T2 ,+Y+".`, LL=R °- OUT S2 1:2 R65 33011 R74 7511 = IN536 I/8A 53 T3 D7 +27V M FI 2N22I 8 VOLTAGE REGULATOR 24 All resistors 1/4 watt, 5% unless noted R1, R49, R52, R71 -4700 ohms R2, R22, R31, R43, R46-potentiometer, 10,000 ohms, linear taper R3, R4, R12, R40 -6800 ohms R5, R37, R38- 56,000 ohms R6, R35, R36-5600 ohms R7, R9, R17, R33, R34, R45, R47, R48, R50, R54- 10,000 ohms R8, R18, R21, R23, R29, R70, R73, R75, R76- 1000 ohms R10- 15,000 ohms R11, R13, R68-470 ohms R14, R15 -1200 ohms R16- 22,000 ohms R19-680 ohms R20, R28, R30-1500 ohms R24, R25- 47,000 ohms R26-100 ohms R27, R42, R60, R61, R62, R63-560 ohms R32, R41-820 ohms R39-2700 ohms R44 -potentiometer, 50,000 ohms, linear taper R51, R59- potentiometer, 5000 ohms, linear taper R53, R64, R65, R72-330 ohms R55 -3900 ohms RRR55587-6-35-911000o,h0om0h0ms oshms R66-27,000 ohms R67, R74 -R7659 -o2h2m0s0, ohms 5 watts Cl, C2-1500 pF, 2 %, mica C3-3000 pF, 2 %, mica C4, C19, C24, C35, C41-.01 F, ceramic C5-56 F, 15 volts, tantalum -5 C6, C7, C20, C29, C31, C32 -0.1 F, ceramic C8, C12, C15, C18, C23, C33 F, 6 volts, C9, tantalum C14, C16, C30, C43 -20 F, 50 volts, tantalum C10-30 F, 15 volts, tantalum C11, C13, C17-100 F, 6 volts, tantalum C21 -4300 pF, 5% mica C25, C26, C27, C28-1000 pF, 2 %, mica C34, C39-1000 pF, ceramic CC3376, -C1358-F3,320pFv,ol5ts%, ,tamnticaalum C40-100 pF, 5 %, mica C42 C22 --580200 ,,F, pF, 30 volts 5 %, mica T1, T2-Three 60 -turn windings on CF111-06 core (see text), Newark Electronics Stock No. 59F1510. $2.05 VAC T3 -24 volts, 0.3 amp transformer (B.A. -3#13A903) T4 -turn primary, 1 turn secondary, #26 Si, Se2,naSm3-eslepdswt itroeg, g3le/1s6w" idtciah form, brass slug D1, D2 -1N276 diode, Hughes D3, D4, D5, D6-1N3064 diode, TI DDD798-1--N11NN595362653B4r,,e6c1.t52if--ivevoor,lltt G.E. Zener, Zener, I.R. Mot. DQ110-2-N1N2252124,0,MMoto.t. or MV1624 (see text) Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10- MPS2923, Mot. Q11- MPS404, Mot. Q12- MPS918, Mot. 1- Q13-2N2218, T.I. IC- MC1531G op amp, Mot. or MC1709C (see text) J1, J3, .15, JJJ624,-pJ-ht7eof-lnobneanfjenaeacdnktsahrJuacks -3" F1 -1/8 amp fuse Case x 5" x 7" aluminum minibox (Bud CU3008A) Miscellaneous: 12 pin printed circuit connec- tor, 300 ohm twinlead, fuse holder, 1/16" single sided p.c. board-4%x6 inches. diodes D3 -D6. This type modulator is doubly balanced with two center -tapped transformers so the 38 -kHz component is canceled at the output as desired. The output of the modulator consists of the amplitude modulation components of the 38 -kHz suppressed subcarrier. Resistors R60-R63 are used to improve balance or carrier suppression. The carrier is more than 40 dB below the input, which is adequate. Transformer T1 must respond past 50 kHz without any resonances. Most commercial audio interstage transformers do not meet this requirement. Therefore, a special toroid transformer was designed. The construction details for this trans- former are in Fig. 6 on page 67. Transformer T2 can be identical to Ti. I used a commercial 2:1 center tapped transformer instead. At audio fre- quencies below 300 Hz the reactance of T2's primary introduces an undesired phase shift which results in decreased stereo separation. This can be improved only at the expense of a larger trans- former winding or by reducing R65 and R64 which requires more transistor cur- rent. A higher current transistor could be used for Q9. sists The total of L +R composite audio, L -mRoduinlaftoiromn actoionn- on the 38-kHz suppressed subcarrier, and the 19 -kHz pilot signal. These are summed together by operational ampli- fier IC1. An op amp is used to give greater than 60 dB isolation between the three inputs. Summing resistors R47, R48. and R66 can be varied to adjust the individual gains of each input. The individual gain is equal to R54 divided by the series resistor. I used an MC 1531 G which is rather expensive. Newer and cheaper op amps are available, such as the MC1709C, and can be used instead. The summer output modulates vari- able-capacitance diode D10, which is part of the resonant tank circuit of the 100-MHz oscillator. The diode, a Motorola 1N5190 Epicap, makes this a voltage-controlled oscillator which results in an FM signal output. The center fre- (continued on page 67) 64 RADIO -ELECTRONICS www.americanradiohistory.com MULTIPLEX GENERATOR (continued from page 64) quency of the oscillator can be varied about ±2 MHz by adjusting the slug in T4. My unit oscillated between 102 and 106 MHz. The exact frequency will be affected by stray wiring capacitance and layout. Be sure to prevent ground currents from modulating the oscillator. This is the reason for the decoupling consisting of R68, C35, and C36. The oscillator is especially susceptible to 19kHz ground currents. Too much leakage will cause the pilot to be transmitted even though R46 is set at minimum. The oscillator output can be suitably loaded with a 300-ohm twin lead. Diode D10 can be any of a number of 10-pF units now available. One low cost unit is the MV1624 ($1.42). The difference in operation between it and the 1N5140 ($5.85) will be a slight difference in modulation .sensitivity but should be negligible. A regulated dc power supply and an ac rectifier circuit is used. The Zener diode reference provides a low output impedance. This is necessary to keep both oscillators at their correct frequencies and prevent power line modulation of oscillator Q12. Construction and alignment The circuit layout is not critical except for the 100 -MHz oscillator, for which component leads should be kept to an absolute minimum. A piece of 300-ohm twin lead connects the oscillator coil to the feedthru terminals in the chassis. The circuit board is laid out so it can be unplugged from the chassis. It is held in place by one screw and a threaded standoff to the chassis. The first step in aligning this generator is to set the frequency of the 19kHz oscillator. The easiest way to do this is to monitor the signal at JI with an electronic counter while adjusting R2. Another way was devised which doesn't require a counter. A 19 -kHz signal is available in all multiplex demodulators when the FM radio is tuned to a station broadcasting stereo. This signal can be used to compare with the generator pilot frequency using the simple phase detector shown in Fig. 7. R2 is adjusted until the phase-detector output contains a - low-frequency beat note. This oscillator can be adjusted for a beat note of around 2 Hz which is plenty accurate meaning the two frequencies are within 2 Hz of each other. One of the phase detector inputs should be greater than 4 volts p-p to turn the diodes on. The chassis cover should be in place for this test in case stray capacitance changes the oscillator frequency. This requires an access hole in the side or back of the unit for adjusting R2. Next, the 38 -kHz filter is aligned by adjusting R51 for maximum output at 011's collector. Oscillation in this type of active filter is possible. Therefore, the 19-kHz oscillator should be disabled by shorting R7 and checking to see that no signal appears at Q11. The ac voltage at Qll's collector should be near 10 volts OCTOBER 1970 CORE :INDIANA GENERAL CFIII -06 60 TRIFILAR TURNS NO 32 ENAMELED WIRE PRI T SEC 6 Fig. 6- TOROIDAL CONSTRUCTION increases bandwidth without resonances. Z=10K 2K CT 19 kHz FROM RECEIVER 1.5K TRANSFORMERS: IOK /2K CT CALRAD CR -70 OR EQUAL .y69kHz FROM GENERATOR 820S1 BEAT NOTE OUTPUT Fig. 7- SIMPLE PHASE DETECTOR eases adjustment of the 19-kHz oscillator. Fig. 11-PILOT AND SUBCARRIER are in phase in this double-exposure photo. p-p and can be adjusted by selecting the value of R41. The next step is to adjust the phase relationship between the pilot signal and 38 -kHz subcarrier. To do this, you must either sync the scope on one of the signals or use a chopper input on the scope if available. The chopped input method allows direct viewing of both waveforms simultaneously. I used another method. The scope is externally synchronized by the 38 -kHz signal at test point TP-1. Then the 38 -kHz waveform here is viewed on the scope and the scope set- Fig. 9-MODULATION WAVEFORMS. a- b- c- Left-only or right-only signal with 1-kHz input at zero pilot level. and Waveforms at J2 with right or left in- puts at 500 and 5000 HZ, respectively. tings adjusted so the sine-wave zero crossing occurs at the center of the grid. Next the scope input is placed at J1 and R3, R4 are adjusted for a zero crossing of 19-kHz at the same point as the 38- kHz waveform. This is shown by the double exposure photo in Fig. 8. Now the pilot signal transmitted is in the proper phase relationship for stereo demodulation. The audio mixing circuits must now be adjusted to give proper stereo separa- tion. First apply a 1-kHz signal to the left channel. The pilot level minimum. The L-+R and L -iRs tusrwnietdchetos must be closed. With the scope input at J2, adjust R31 until one of the 1 -kHz envelopes is minimum in amplitude as shown in Fig. 9-a. Figures 9-b and 9-c show the same point for audio input fre- quencies of 500 Hz and 5 kHz respec- tively. These photos demonstrate a sepa- ration of about 40 dB. Next, remove the signal from L and apply to R only. A waveform similar to Fig. 9 will appear at J2 when R22 is adjusted for max- imum separation. The only calibration remaining is the 19-kHz pilot level required to give the proper oscillator deviation. I determined this with the help of an FM stereo re- ceiver. For this measurement the L-I-R and L-R switches are in the OUT posi- tions. Somewhere in the receiver multi- plex you can check the 19 -kHz level being received from the discriminator with a scope. Knowing this level, you can receive the signal from this multi- plex generator and adjust the pilot level to equal that from a broadcast station. The exact level is not extremely impor- tant but some multiplex demodulators are sensitive to pilot level as separation is affected. I found that 0.2 volt p -p 19 kHz at J1 output is correct and should be accurate enough for alignment. At this point the knob on the PILOT LEVEL control was adjusted to read "CALI- BRATE." I found it convenient to place (continued on page 83) 67 www.americanradiohistory.com CAREERS in ELECTRONICS blueprint to your future You're a technician today, but you don't have to still be a technician tomorrow. Here are some of the other doors open to you by L. L. FARKAS' Last month we introduced the service technician to several other kinds of jobs that he is qualified to handle. This month we present ten more opportunities for the future. They take training, but they are available. Cenogminpeueter /rpfrioegldramer The technician who has worked on computers and has a good knowledge of their theory and operation can often find a job as a computer field engineer. In this position he will service computers leased or sold by a computer company within a certain region. Such service includes preventive maintenance, troubleshooting and repair, and helping the customer determine what additional equipment he may need to perform specific tasks. Normally the computer company hiring a technician will send him to school to learn the intricacies and operation of their product. It will help the technician also to learn computer programing. With this additional knowledge he can help his customer further in establishing various programs which in turn may mean the sale of additional computer components or subsystems. Computer programing courses are available at many schools and all the technician needs is the desire to enroll in such a course and the tenacity to complete it. If he happens to be working on computers at the time, he can readily obtain programing experience that will help him progress on the job. Equipment sales The equipment sales field can be interesting and profitable to the technician who has sales ability. There is, of course, the job of salesman in an electronic supply house, where knowledge of part characteristics and usage is a must. Here the technician must know what new parts are available and can be used, or what substitutions can be made to meet a customer's design or operating requirements. He may also work as a salesman of various types of electronic equipment or electronic systems. In this last function he will often have to contact top officials of companies and government to whom he will have to demonstrate and sell his product. To do this effectively he will have to be able to speak well, but over and above this, he *Martin Marietta Corp., Vandenberg Operations 68 must know how to plan and implement a good presentation or demonstration. The training for this type of work, besides gaining a thorough technical knowledge of the equipment, includes courses on salesmanship, audio -visual aids, creative thinking and psychology. Again, such courses are generally offered by community evening programs. Junior or associate engineer Courtesy Cleveland Institute of Electronics To the technician who wants to further his career in the technical area of electronics the next logical step is to become a junior or associate engineer. In the past there were many opportunities for promotion to this level simply on the basis of experience on the particular equipment or system being produced. In the last few years, however, companies have tightened their educational requirements so that promotion to a junior or associate engineer level requires at least an associate science degree that includes courses in math, physics and chemistry. Most companies encourage technicians to update their education to this level. Some firms offer refunds or provide loans for college tuition. The smart technician will take advantage of such help. Even at the rate of one course per semester, credits accumulate fast and soon the technician will find he has gained the education that permits him to progress. Radio operator An electronic technician can also become a good radio operator. Certainly it shouldn't take him long to learn the operation and maintenance of commu- nications transmitters and receivers, motor generators, radar and other electronic equipment used for communications and navigation. Radio operator jobs can be found at fixed installations, such as a shore or airport radio station, in aircraft and on ships. Some operators are also used in airplane blind-landing systems. The radio operator must pass an examination given by the Federal Communications Commission to obtain a radio telephone or telegraph operator's license. For the telegraph endorsement the operator must take a code test in which his code sending and receiving skill is checked. For all licenses he must pass a test on the theory and operation of equipment and his knowledge of communication laws. A radio operator on board a ship or aircraft is an officer with great responsibility. He must insure that his equipment is always in good operating condition and be ready to make emergency repairs. A number of technical schools provide courses leading to a radio operator's license. Subjects covered include basic electricity, theory and operation of communications components and systems, theory and operation of radar systems and code practice. In most cases the electronic technician covers these courses pretty fast, needing only the code practice and a knowledge of FCC laws to meet the requirements of the FCC examinations. Of course, if your hobby is amateur radio, you may be able to short-cut the education span since you'll already have acquired most of the necessary knowledge and practice in communications. Circuit draftsman Courtesy RCA Institutes An interim step between a tech- RADIO-ELECTRONICS www.americanradiohistory.com nician and engineer can be taken via the drafting route. Here the technician can work on layouts of electronic circuits and, in some cases, as he gathers knowledge and experience, he may be given some original circuit design. This type of job requires a basic knowledge of drafting methods which can be obtained in high schools or in trade school evening classes. Of course, if the technician wants to progress from there to engineering he will also have to acquire the training and education indicated for junior and associate engineers. Broadcast or television engineer Courtesy Cleveland Institute of Electronics The electronic technician looking for different and interesting work should investigate technical positions with radio broadcasting or television stations. He can work in the studios, the master control room, in the field or at the transmitter. The studio engineer sets up microphones and cameras, and then controls gain and mixes audio or video channels. The master control engineer monitors and switches programs from different studios, field pickups or other remote locations. The field engineeer puts on broadcast or television programs from remote or field locations. He uses portable or mobile equipment to make pickups from the ground. air or from ships. Transmitter engineers must have an FCC operator's license since they handle the operation, maintenance and repair of one or more high-powered transmitters. Maintenance engineers handle the maintenance, troubleshooting and repairs of all radio broadcast or television electronic equipment, except perhaps in the area of the field engineer. The field engineer, distant from station facilities, must not only operate his field equipment, but also do all the maintenance and emergency repairs to insure "the show always goes on." Training for all these areas is based upon a series of courses, usually given at a technical school, which progresses from electronic and electrical component basics to broadcast and television systems. In this type of work the electronic technician can usually start as a maintenance engineer and then, as he gains experience with equipment, assume the position at the station that fit his interests and temperament. Often he does OCTOBER 1970 not have to take the formal training, obtaining all the information he needs by self-study and practice. Instructor Courtesy RCA Institutes A natural evolution from technician on a specific electronic subsystem or system is that of an instructor on that equipment. Having worked on the hardware, troubleshot its defects and performed its maintenance, the technician should be able to tell others about it. However, teaching calls for certain capabilities: The teacher should be able to describe the components of the equipment and discuss their theory of operation. This is not as easy as it sounds, for often a man can keep a piece of equipment operational without knowing exactly how it works. Thus before doing any teaching the technician must review the equipment in detail to make sure that he understands exactly how it operates. The teacher must have the skill of imparting his knowledge to his students. Most companies using technical instructors provide a short course in methods of presentation which include handouts. visual aids and practice in the best ways of making the subject interesting. Part of the instructor's job entails gathering the technical material he needs and compiling it in a student guide. This guide can vary from a series of outlines and line drawings to a detailed book of instructions, depending on the time allocated for its completion. To do this effectively, the technician should be able to write on technical subjects and to organize his written material. He should also be able to create or arrange visual aids to enhance his presentation. Public speaking experience or training will also help to make his lectures informative, while courses on effective writing or technical writing will be invaluable in handling his written work. Other tasks that the instructor must perform are: to write examinations, test his students. then grade the papers. An analysis of the results will then help him determine the success of the course. A number of training and evaluation methods can be learned by taking a basic education course. Training coordinator Just as important as the instructor on an educational program is the training coordinator. He plans and establishes the technical training program for his company. This entails determining the need for courses, obtaining course outlines, scheduling the courses, arranging for classrooms and necessary classroom equipment and insuring competent instructors are assigned. Once classes are organized he must enroll students, review student guides, even monitor classes to check on the quality of the instruction. Finally, he must establish and keep records on the results of examinations taken by the students so technical personnel can be fully trained to perform required tasks. To do this type of work a technician must be able to plan and take care of details. Rather than performing many of the functions, he coordinates them. He must also be able to set up and maintain records and communicate with supervisors to make sure they are aware of the training program and have taken the steps necessary to make their workers attend the courses. For the evaluation of courses he should be capable of putting himself in the place of the students and, based upon his own knowledge of the technical subjects, determine whether the instructor is providing the explanation and details necessary to understand the subject. Here the technician's experience will provide a basis of reference. Educationally, a course in business management will be useful in providing data on planning and implementation of various types of tasks and handling personnel. Technical writer If a technician has an aptitude for writing he can become a technical writer. Having worked with test procedures he should have a good idea of their form and content. Of course he does not necessarily have to originate them. Rough test procedures, or at least test specifications, are generally written by engineers. His task is then to place them in the step -by -step format used by technicians in testing equipment. With his experience he should have little difficulty. Another technical writing area is handbooks and technical manuals. These are more complex than test procedures as they generally cover simplified equipment operation, theory of component functions, setup and operation of equipment and maintenance routines. Normally the technical writer works with the engineers who designed the equipment and then with the men who set the first model in operation. He gathers a great deal of technical information from which he writes a rough draft of the manual. Once this draft has been reviewed by various project personnel, the writer corrects and finalizes the manual, making sure illustrations and photographs are included to clarify the text. A number of courses and books on technical writing are available in evening education programs. Probably one of the toughest jobs a ( continued on page 90) 69 www.americanradiohistory.com NEW PRODUCTS More information on new products is available from the manufacturers of items identified by a Reader Service number. Use the Reader Service Card on page 92 and circle the numbers of . the new products on which you would like further information. Detach and mail the postage -paid card. Nothing replaces the reality of personal in- class" instruction. It builds your confidence through thorough preparation. P rofessional success depends upon the quality of your training. You owe yourself the best. Anything less will be costly, takes much longer and requires more effort from you. Take the shortest distance between you and your career. You'll be ahead in every way. FREE LIFETIME PLACEMENT VETERAN APPROVED HEALD Engineering College 1215 Van Ness Ave., San Francisco, California 94109 Oldest and Largest Institution ofits kind in the United States. (Since 18631 Please send information on: HEALD ENGINEERING COLLEGE Bachelor of Science Degree Courses (36 months) Electronic Engineering Electrical Engineering DMechanical Engineering Civil Engineering DArchitecture (42 months) HEALD INSTITUTE OF TECHNOLOGY A division of Heald Engineering College Technology Diploma Courses DElectronic Engineering Technician (FCC) (15 months) DRadio-Television Technician (FCC) (15 months) DMechanical Drafting (12 months) DElectrical Drafting (12 months) Structural Drafting (12 months) Name Age Address City State Zip Phone J Circle 20 on reader service card 70 BUDGET AUTOMATIC TURNTABLE, Garrard model SL72B, includes all features of Garrard's top unit. Uses a low -mass tubular aluminum pickup arm that floats almost friction free on needle pivots. The adjustable counterweight is isolated from the arm to damp out resonances. Has three fingertip tabs for operation. One for automatic play of up to six records, the second turns the motor on and off, and the third activates cueing and pausing, viscously damped in both manual and automatic modes, with viscous damped tonearm descent in the automatic mode for the first time in turntables. Also features an antiskating device and a sturdy record support platform.-$89.50-Garrard British Industries Co, Westbury, NY 11590 Circle 31 on reader service card STEREO AM /FM TUNER KIT, model KG-/96, Easy-to -follow instructions require soldering connections between circuit boards. Includes all silicon transistors a tuning meter and edge -lit tuning dial. FM -IHF sensitivity, 3µV; AM, 50µV. Complete kit plus dipole antenna, $79.95 -Allied Radio Corp. 100 N. Western Ave., Chicago, Ill. 60680. Circle 32 on reader service card FIX -IT TOOLS, with special applications in the servicing of radio, TV and hi-fi sets include a pair of long (20X") fixed handle, hollow-shaft nutdrivers with hex openings of fl" and 5/48' to simplify work on color TV tuners, bezels, and other components where the only access is through the back of the set. Two interchangeable g" and X" external hex Palnut driver shanks which fit all Xcelite 99 handles including Tee and ratchet type are also offered. For fast tip cutting of fine wires, a pair of miniature close-cutting diagonal pliers, 4 inches long, for electronic assembly operations as well as service work. -Xcelite Inc., Orchard Park, New York, NY, 14127 Circle 33 on reader service card STEREOPHONES, model SP-8: Earcups are soft rubber cushions, headband has easy-to- adjust design, transducers are 2 inches. Frequency response is 2518,000 Hz with 0.3 watts output, im- pedance is 8 ohms. 11 ounces complete with 6-foot coiled cord and standard fi" phone plug. In kit form, $8.95 -EICO Electronic Instrument Co., 283 Malta St, Brooklyn, N.Y. 11208 Circle 34 on reader service card COMPONENT CLIPS -Hold Tite, feature a split bulb at its base that locks into printed electronic assembly boards to hold and insulate capacitors, resistors, lamps, batteries, fuses and other parts. RADIO -ELECTRONICS www.americanradiohistory.com Special introductory offer to new members of the ELECTRONICS AND CONTROL ENGINEERS' BOOK CLUB 11RC!If1S`` EIECIiBÌÌ41G 404/437 SOURCEBOOK OF ELECTRONIC CIRCUITS by J. Markus Pub. price, $19.75 Club price, $14.75 A494/754 ENGINEERING MANUAL, 2/e by R. H. Perry Pub. price, $12.50 Club price, $10.65 391/432 DISPLAY SYSTEMS ENGINEERING by H. R. Luxenberg & R. L. Kuehn Pub. price, $16.50 Club price, $11.95 A523/401 CHARACTERISTICS AND OPERATION OF MOS FIELD EFFECT DEVICES by P. 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Sent to members without cost, it announces and describes in detail the Club's featured book of the month as well as alternate selections which are available at special members' prices. When you want to examine the Club's feature of the month, you do nothing. The book will be mailed to you as a regular part of your Club service. tions-or if you want If no you prefer book at all one of the alternate for that month-you selecnotify the Club by returning the convenient card enclosed with each Bulletin. As a Club member, you agree only to the purchase of four books over a two -year period. Considering the many books published annually in your field, there will surely be at least four that you would want to own anyway. By joining the Club, you save both money and the trouble of searching for the best books. Please enroll me as a member of the Electronics and Control Engi- neers' Book Club and send me the two books indicated below. I am to receive the bonus for just $1.00, and my first selection at the special Club price shown. These books are to be shipped on approval, and I may return them both without cost or further obliga- tion. If I decide to keep the books, I agree to purchase as few as four additional books during the next two years at special Club prices (approximately 15% below list). Write Code No. of bonus book here Write Code No. of first selection here Name Address City State )ip E 33145 Circle 61 on reader service card OCTOBER 1970 71 www.americanradiohistory.com COMPUTER BOARD SPECIAL Easy to remove. Dimpled sides assure a tight holding action. Clips snap into holds .125" to .156" diameter. Available in sizes % ", %", %", and ií ". Made of virgin nylon, will accommodate over -size parts as well.-Lorain Tool & Mfg. Co., 1817 Iowa Ave., Lorain, Ohio 44052. Circle 35 on reader service card Stock No. B9082 Honeywell Computer boards, 41/2"x12". Transistors, diodes, zeners, capacitors, precision resistors, heat sink, trimmers etc. 2 Different boards $1.00. 3 lb. Stock No. B9093 Honeywell Power Board contains 4 2N1137B 80 watt PNP power transistors, 8 Top Hat diodes. 8 precision resistors and 4 IN642 diodes $1.25 ea. 2 lb. Stock No. 9094 Honeywell Boards 51/2" x 6". Loaded with late no. transistors, diodes, resistors and capacitors. 2 different boards $1.00. 2 lb. COLOR TV SERVICE AC- CESSORY, model B -150. Single-Brite gun control, permits the restoration of color picture balance when a single color gun weakens prematurely. The potentiometer -type device lets the technician adjust the bias between the GI and G2 grid leads of the weakened gun, per- COMPUTER GRADE CAPACITORS B2040 Sangamo or Pyramid 41/4" x 13/4" 4000 MFD 50V 50 B2039 Pyramid 41/4" x 3" 6000 MFD 75V 75 B4016 FET Field Effect Transistor To-18 25 Volt Source to Gate N Channel .. .50 B4017 Tunnel Diode Similar to 1N3717 .50 5/2.00 3/2.00 5/2.00 5/2.00 $1.00 FREE WITH $10.00 ORDER Lots of other items-send for free flier; all mer- chandise fully guaranteed. Please include postage; excess will be refunded. DELTA ELECTRONICS. CO. BOX 1, LYNN, MASSACHUSETTS 01903 Circle 62 on reader service card mitting color intensity variation as needed for balanced picture. Easy installation requires two simple connections and no soldering.-PermaPower Div., Chamberlain Mfg. Corp, 845 Larch Ave., Elmhurst, Ill. 60126 Circle 36 on reader service card FOGHORN /HAILER, Model MD -19 has 5 functions. Is a foghorn, boathorn, hailer, listener, and with MDA-19-1 speaker becomes an intercom. Has pushto-talk mike and weather-proof speaker with mounting base. Operates from 12 V. Includes mounting bracket and 20 ft. of cable. Kit $84.95, accessory speaker $9.50.-Heath Co. Benton Harbor, Mich. Circle 37 on reader service card PROFESSIONAL TAPE DECK, model CAD5, tape cassette recorder incorporates the Dolby -B noise reduction processor as part of the record and play- No. 111 ESPECIALLY MADE FOR TELEVISION TUNERS POSITIVE CONTACT p.EANER AND LUBRICANT CONTINUOUSLY CLEANS AND LUBRICATES CONTACTS EACH TIME TUNER IS ROTATED NON -CORROSIVE MON- DRYING NON-CONDUCTIVE NON -EVAPORATING Size i-i 72 LUBRA CLEAN .. A T.V. TUNER CLEANER THAT REALLY WORKS! MADE ESPECIALLY FOR TELEVISION TUNERS Finally , a tuner cleaner- that really -works. Apply LU CLEAN and let it do the work for you. Physical isa polishing contacts is no longer necessa LUBRA. CLEAN continues to T$I I . i4cate t a lloerfs ef tacts for months aftm failed. Sold leaners an b av e $2.98 per JJjA t P COrttli CLEAN COMPANY P. O. BOX 926 - MARTINSVILLE, VA. 24112 - PHONE (703) 638 -1211 Circle 63 on reader service card RADIO -ELECTRONICS www.americanradiohistory.com The new er antenna from RCA has: "Long-lasting" element/ feed line connections. Waterproof, polypropylene insulators that pivot. Integrated UHF bow tie. Rigid, square boom. Tough vinyl finish. That ought to prove RCA is serious about the antenna business. OCTOBER 1970 So serious we've set up a new production facility at our Memphis plant. But before we manufactured a single antenna, our engineers literally started designing from scratch. The result? Permacolor. Here are just a few reasons why RCA Permacolor antennas are different, and are an improvement over what you're now selling. 1. Durable connections /Perma -tuned circuits. All active elements (many perform more than one function) are solidly connected to a symmetrical aluminum feed line by riveted straps. This reduces reception failure due to flimsy or intermittent connections. 2. "Single unit" insulator/element. Insulators are polypropylene. Elements extend 51 inches into the insulators. Elements and insulators pivot as a unit-lock in place-have no loose connections. No high stress points. 3. Bow tie and 110° corner reflector UHF Section integrated into a single downlead for better UHF reception. 4. Easy installation. Simply unfold and install. Permacolor antennas go up in one piece. No bag of bolts. Nothing to take apart and reassemble. Snap -off elements let you quickly tailor the antenna to reception requirements. 5. Tough, handsome blue and gold vinyl coating protects against weather and airborne chemicals. The new RCA Permacolor Antenna is the antenna you can put up for good. See it now at your RCA Parts and Accessories distributor. Ì Parts and Accessories, Deptford, N.J. RC,' 73 www.americanradiohistory.com Introducing the world's only $339 triggered scope. Before you say you don't need a triggered scope, look what's happening to TV servicing: tubes are out, transistors and IC's are in. With tubes you could play hit -or-miss, knowing the tube would take the overload. Try the same thing now, and good-bye transistors. For new-era circuitry, Leader introduces a new era troubleshooter. A triggered scope, just like the ones the TV designers use. Now the wave shape is locked in and continuously displayed. Now you can look at a waveform containing high and low frequency components. Now you can determine voltage directly and instantly. Before you say $339 is a lot of bread, look what it buys: Leader's LBO -501 5-inch triggered scope, with a bandwidth of DC to 10MHz and a solid state package. Going like hotcakes at your Leader distributor. Seeing is believing. back electronics. Extends in frequency response beyond 12.5 kHz. Acts as a compressor/expander only without its inherent weakness. The Dolby processor boosts low-level, high-frequency signals before they are recorded and then attenuates these signals in a mirror image during playback. Electronic speed control assures minimum speed variation with reduction of wow and flutter. Professional sliding potentiometers set recording level and the recording overmodulation light works in conjunction with the dual recording meters and flashes when the sound level is too high. Automatic digrtal 'counter with pushbutton reset, records andR plays back i>1, mono and stereo, pushbutton switches_for all functions.-$229.95-Harman- Kardon, Inc. 55 Ames Court, Plainview, LI, N.Y. 11803 Circle 38 on reader service card COMPACT TV CAMERA, model TVC-500. Develops clear, sharp monochrome pictures in video or rf signal at a switch -selected output. Video is viewed on a monitor but when the camera is switched to rf output, the pictures are displayed on a standard TV receiver. Simple screwdriver adjustment selects output frequency covering channels 2 through (3. Output level on a composite LEADER INSTRUMENTS 37-27 27th Street, Long Island City, N.Y. 11101, (212) 720 -7411 Circle 64 on reader service card NO COMPETITORS Nobody else but EMC designs in so much value Compact, lightweight portability. Use it on the bench or in the field. Full -view meter gives ....direct, clear -cut qual- ity indications. Three heavy -duty controls for quick set -up of all tests. Check a fistful of tiut beosfteinn the time takes to test one. 12 slide switches for individual selection of tube pins provides versatility In testing. prevents obsolescence. Full comple- ment of sturdy sockets accepts compactron (12pin), nuvistor, nover, 10 -pin, 9[mo-pcinitnai,al,toucartnaedl, tubes. r P e c i s e progr a m m i n g. Only one socket pceornftiugbuera-btiaosne pdreenvteanl tpsluga-cinc.i- THE MODEL 213 saves you time, energy, money Checks for shorts, leakage, intermittents, and quality Tests u all tube types including magic eye, regulator, and hi -fi tubes Checks each section of multi -purpose tubes sep- arately Gives long, trouble -free life through heavy -duty components, including permanently etched panel Your best dollar value in a tube tester. Available in high- impact bakelite case with strap: $33.40 wired; $21.90 in kit form. Wood carrying case (illustrated) slightly higher. EMC r' 1 E M C, 625 Broadway, New York 12, N.Y. Rush me FREE catalog describing all EMC value -loaded test instruments and name of local distributor. NAMF ELECTRONIC MEASUREMENTS CORPORATION 625 Broadway, New York 12, New York Export:Pan-Mar Corp.,1270 B'way,N. Y. 1, N. Y. ADDRESS CITY 7ONE_STATF 74 signal is 1.4 V 1)-p, s idco is 1 V p-p. Hf output is greater than 29.5 dBmV (30mV) and impedance is 75 ohms. Horizontal resolution of center is 550 lines on video and 300 on rf output. Each 6 pound camera is supplied with a 25 mm F /1.8 lens. Wide angle and telephoto are available. $325.00-Jerrold Electronics Corp., 401 Walnut St., Philadelphia, Pa. 19105 Circle 39 on reader service card PROFESSIONAL MICROPHONES, models 860 and 860s. Ball-head omnidirectional dynamic mikes incorporate an integral "pop" and "blast" filter. The RADIO- ELECTRONICS www.americanradiohistory.com Modular Color Television! Exclusive Modular Design ... Circuit Boards snap in and out in seconds for easy assembly, simple servicing 3-stage IF assembly Gun shorting switches Tilt -out convergence/ secondary control panel Plug -in AGC /Sync circuit board Plug -in 3.58 MHz Oscillator circuit board Exclusive Check -out meter Plug-in Chroma circuit board Plug-in Luminance circuit board Service and Dots switches Hi -fi sound output Master control panel Plug -in Video Output circuit board High Voltage Power Supply Plug-in Sound circuit board Circuit breaker protection Conservatively -rated power supply components Plug-in wiring harnesses and connectors for easier assembly Plug -in Vertical Oscillator circuit board Plug-in Horizontal Oscillator circuit board Plug-in Pincushion circuit board New Expedited 48 -Hour No- Charge Warranty Service Plan for Solid State TV Modules! Special service facilities have been established at the factory and all Heathkit Electronic Centers to expedite service and return of Solid -State TV circuit modules within two working days. During the 90 -day warranty period, TV modules will be serviced or replaced with no charge for labor or parts. After the initial 90 -day warranty period expires, TV modules will be serviced or replaced at a fixed charge of $5.00 per module for labor and parts for a period of two years from date of original kit purchase. Add extra convenience and versatility to your new GR -270 or GR -370 Solid -State Color TV with this new ultrasonic remote control kit. Lets you turn the set on and off, adjust volume, change VHF channels and adjust color and tint from the comfort of your chair. Assembles and installs complete in just a few hours and the built-in meter on the receiver makes final adjustment a matter of minutes. Kit GRA -70 -6, 6 lbs. $84.95* Choose One Of These Handsome, Factory Assembled Cabinets 3 models in 295 sq. in. Luxurious Mediterranean Cabinet... factory as- sembled of fine furni- ture grade hardwoods and finished in a flaw- less Mediterranean pe- can. Statuary bronze trim handle. 30-1/32" H x 47" W x 173/4" D. As- sembled GRA-304-23, 85 lbs. $129.95* Deluxe Cabinet .E.a.fralyctAomryericaasn- sembled of a special combination of hard- woods & veneers and finished in classic Salem Maple. 29-21/32" H x 371/4" W x 193/4" D. As- sembled GRA-303.23, 67 lbs. $114.95* Contemporary Walnut Cabinet... factory assembled of fine veneers & solids with an oil rubbed walnut finish. 29. 17/32 "H x 35- 13/16" W x 197/e" D. Assembled GRA-301-23, 56 lbs. .. $74.95* 3 models in 227 sq. in. ... Exciting Mediterranean Cabinet assembled ' using fine furniture techniques and finished in stylish Mediterranean pecan. Accented with statuary bronze handle. 27- 31/32" H x 417/e" W xG1R9A--92/0126-2"0,D.7A0 slsbems.b.l.e.d. $114.95* Contemporary Walnut Cabinet and Base Combination. Handsome walnut finished cabinet sits on a matching walnut base. Cabinet dimensions 20- 31/32" H x 317/16" W x 183rá" D. Base dimensions 73/4" H x 273/4" W x 183/4" D. Assembled GRA-203-20 Cabinet, 45 lbs. $49.95* GRS-203-6 above cab. w/ matching base, 58 lbs. $59.95* Handy Roll- Around Cart and Cabinet Combina- tion. Features the GRA- 203-20 walnut cabinet plus a walnut- trimmed wheeled cart with stor- age shelf. Assembled GRA-203.20 Cabinet, 45 lbs. $49.95* GRA-204-20 Roll -Around Cart, 18 lbs $199..9955"* GRS- 203 -5, Cart & Cabinet 6t Combo, 58 lbs. $59.95* s:s,l "''' ,cti NEW FREE 1971 CATALOG! Now with more kits, more color. Fully describes these along with over 300 kits for stereo/hi -fi, color TV, elec- tronic organs, guitar ampli- fiers, amateur radio, marine, educational, CB, home & hobby. Mail coupon or write Heath Company, Benton Har- bor, Michigan 49022. I HEATH COMPANY, Dept. 20 -10 Benton Harbor, Michigan 49022 Enclosed is $ Please send model (s) Please send FREE Heathkit Catalog. Name a Schlumberger company , plus shipping. Please send Credit Application. Address City State Zip *Mall order prices; F.O.B. factory. Prices & specifications subject to change without notice. CL-392 L-Circle 68 on reader service card OCTOBER 1970 81 www.americanradiohistory.com It's yours ?U2S:E!N APPIFBEE l' 11:1: for the asking! J;fi- GIANT 260 PAGE 1971 RADIO -TV ELECTRON ICS CATALOG YOUR BUYING GUIDE FOR EVERYTHING IN ELECTRONICS! BURSTEIN W-AriPtePrLo:EBEE CO., DEPT. RE -10, 3199 MERCIER ST., KANSAS CITY, MO. 64111 EName Address City State Zip Code COMING NEXT MONTH NOVEMBER 1970 Lowdown on Alarm Systems Quick guides to which system is best suited to your application. Plus how they work details and installation tips for everyone. Circle 69 on reader service card UNEXCELLED! THE UVM ANTENNA UHF -VHF -FM COLOR Combination UHF- VHF -FM Antennas tat sub ¢tiat rettatmaKC¢. Tuned and engineered featuring a LOG PERIODIC VHF section incorporating a PATENTED MAGNETIC WAVE design for UHF. Discriminate between desired signal and unwanted noise. An absence of minor lobes and extremely high front to back ratio are characteristics of these antennas. Mechanical features include all new fittings and special alloy aluminum tubing for added strength. Six models available. Write or phone for complete information. S & A ELECTRONICS, INC. 210 W. Florence St. Phone (419) 693-0528 Toledo, Ohio 43605 Circle 70 on reader service card 82 Mini -Kits Are Fun You name the circuit -it's prob- ably available as a mini -kit. These low -cost circuits are a fun -packed introduction to electronics. Careers With Computers A look at the opportunities in the computer field today. Based on an interview with Ken Strandberg, manager of G -E's Field Engineering Department. PLUS: Jack Darr's Service Clinic How To Putter With The PUT Power Tool Reference Manual RADIO- ELECTRONICS www.americanradiohistory.com MULTIPLEX GENERATOR (continued from page 67) an access hole in the chassis to permit external adjustment of T4's slug. This allows changing the oscillator frequency to a spot where no local station is operating. Using the generator The composite modulation output is used mainly for applying the stereo signal to a multiplex demodulator for checking it separately. For this, the 19kHz level is not calibrated and must be set to a predetermined level which the discriminator will supply from broadcast stations. This is also true for the remaining composite signal level. The audio input levels to the generator must be kept below about 1.5 Vrms or saturation occurs. regtest value ¿'1 SCUll for every PA application Precision has led the field in quality and de- pendability for 25 years. Most trouble-free line in the industry, Precision offers a complete range of amplifiers in every power range including mobile, and a complete line of accessories. From the smallest office to large auditorium or industrial installations, Precision gives maximum flexibility and performance. ..,.P R E C I S I O N vg POWER TRANSFORMER AND JACKS are on front panel with the pots and switches. Receiver separation versus frequency can be checked between 300 Hz and 20 kHz with this generator. This also provides a convenient way to determine if the receiver de- emphasis circuit is correct. The easiest way to measure receiver separation is to apply an audio tone to only R or L of the generator and measure the ratio of outputs on L and R at the receiver. . NAME g. ADDRESS CITY DIVISION OF PRECISION ELECTRONICS, INC. 9101 KING STREET. FRANKLIN PARK. ILLINOIS 60131 MAIL THIS COUPON NOW ! STATE ZIP C úrir 71 ,, on rïY RMt reader fiR M service card st 111 TUN-0 -FOAM KEEPS CLEANING & LUBRICATING CONTACTS EACH TIME THE CHANNEL IS CHANGED COMPONENTS ON PLUG -IN BOARD are visible when the rear cover is removed. The rf VCO in this unit is very convenient. It lets you check the effect of i.f. amplifier selectivity on overall separation. It also lets the technician adjust a multiplex unit incorporated in the radio without disconnecting it. A direct connection from the rf output is not required as the receiver will pick up the signal from a few feet away. This stereo generator will result in a professional alignment job on any FM stereo receiver. Its relatively low cost and versatility make it a valuable piece of test equipment for any technician. R -E OCTOBER 1970 - Removes miniature soldered compo- nents in seconds without damage Hollow tip fits over connection; vacuums all solder for easy removal of component. Leaves terminals and mounting holes clean. Then, with 360° contact, it resolders faster, better than regular irons. Handles miniature and standard components in PC boards and conventional wiring. Self-cleaning. All parts replaceable. 40 watts, 120-v. Standard tip supplied, 5 other tip sizes available. Pays for itself. $11.95 net East of the Rockies. Larger model available. See your distributor or write: ENTERPRISE DEVELOPMENT CORPORATION 5127 E. 65th St. Indianapolis, Ind. 46220 Circle 72 on reader service card QAM{NG ACTi9R UNO' OAM ALLTUNERS IT wi .%u-n IT REALLY WORKS! 6 MONTH NO CALLBACK GUARANTEE! 1260 RALPH AVE. BROOKLYN, N.Y.11236 For Export: Roburn Agencies Inc.. New York. N.Y. Circle 73 on reader service card 83 www.americanradiohistory.com This Christmas Give Security : =+ Gift selection can be a problem. This year give a gift that will be truly appreciated . . . Security. DeltAlert ultrasonic intrusion detection security. Burglary and vandalism are constant threats to your home, office or shop. With DeltAlert on the job, you have dependable and economical security. A silent ultrasonic blanket guards 150 to 300 square feet of critical space in the home or business. When the ultrasonic blanket is disturbed by motion the system is activated, lights go on, and the separate DeltaHorn emits an earsplitting noise ... frightening off even the boldest intruder. These sturdy units, finished in handsome walnut veneer, are maintenance free and plug right into the wall socket. The DeltaHorn plugs directly into the DeltAlert. Small, the DeltAlert is only 103/8 "w x 31/4 "d x 31/4 "h and the DeltaHorn, 31/4" square, the units blend inconspicuously into your decor. This Christmas, give a lasting gift of security... security for your friends, your family and yourself. Order your DeltAlert Security today! DeltAlert Only $6995 ppd. DeltaHorn Only $2495 ppd. "Delta Products, One Of America's Finest Names In Electronics" /A DP 70-21-1 DELTA PRODUCTS, INC. P.O. Box 1147 RE / Grand Junction, Colo. 81501 (303) 242 -9000 Please send me literature immediately: D Enclosed is $ Ship ppd. Ship C.O.D. Please send: DelAlert(s) @ $69.95 ppd. Please send DeltaHorn(s) @ $24.95 ppd. Name Address LCity /State Zip J Circle 74 on reader service card 84 POWER SUPPLIES SINGLE: PS -61C DOUBLE: PS -62C TRIPLE: PS -63C -Economical, contin- uously variable power supplies by BLULYNE. -Modern walnut finished lrr iliaa p cabinets with beige panels. -Excellent regulation and ripple characteristics. -Single, dual, and triple units available. -Short circuit protected -electronic current limit- ing. Short circuit cannot harm unit. -Grounding cord for added safety. -Floating outputs on all units -ground either plus or minus. -Uses include life testing, production line testing, schools, labs, experimentors use, instructors, technicians, engineers, troubleshooting, battery elimination, and many more valuable uses. PS-61C Single Unit -15 Plus or Minus 1 VDC, 0.700 mA. Usable to 1000 mA. Ripple: less than 0.005Vrms max. PS -62C Double Unit Same characteristics as Single unit above for EACH of two outputs. Two completely independent supplies to be used in any Up to combination. 30 VDC -Up to 2 Amps. PS-63C Triple Unit Same characteristics as Single unit above for EACH of three outputs. Three completely independent supplies to be used in any Up to 4c5omVbDiCna-Utiopn. to 3 Amps. All supplies are fully safety designed. PS-61C PS-62C PS -63C ;49.95 74.95 99.95 Write for illustrated literature on this and other BLULYNE products. Blulyne Electronics Corporation Dept. R. 3 Sand Springs Road Williamstown, Mass. 01267 Circle 75 on reader service card ELECTRONICS - Fill in coupon for a FREE One Year Sub- scription to OLSON ELECTRONICS Fantas- tic Value Packed Catalog Unheard of LOW, LOW PRICES on Brand Name Speak- ers, Changers, Tubes, Tools, Stereo Amps, Tuners, CB, Hi -Fi's, and thousands of other Electronic Values. Credit plan available. NAME ADDRESS CITY STATE GIVE ZIP CODE If you have a friend interested in electronics send his name and address for a FREE sub- scription also. OLSON ELECTRONICS Dept. L1, 260 S. Forge Street Akron, Ohio 44308 Circle 76 on reader service card Service By JACK DARR SERVICE EDITOR Signal Tracing Transistor TV I've read a lot of articles, including some of yours and I still haven't found an easy way to check a transistor TV, stage by stage, with only a vtvm. I've been doing this for years in tube TV's. Why can't I do it in solid-state stuff?-H. J., Highland Falls, N.Y. Several reasons. First and most important, is the different method of construction-PC boards vs terminal - point wiring. Second, the transistors are soldered in. Can't pull 'em and replace with a known good one without a lot of trouble. So! Use the same methods you've used for so long, but use a different test-instrument. The scope! It is just as simple as a vtvm. When you find out where the signal stops, then use the vtvm. Dark Bars On Left Of Raster I have a Zenith. 14N27 portable, which has a dark bar at the left side of the raster. I can more it back and forth with the horizontal hold control. It has what looks like vertical retrace lines near the top of the screen. My customer says this has been there ever since he got the set. All tubes have been replaced, parts checked, shields tightened, etc. -B. T., Bayonne, N.J. After you recheck the horizontal afc and run a complete horizontal os- cillator /afc setup adjustment, and check the afc tube grid bypass capacitor, check the yoke. In a very few cases, we've found that a defective yoke can cause troubles something like this. Never pinned down the exact cause; could be too much air -gap or something in one of the windings, but a new yoke often cures it. Too Much Capacitance? Following a suggestion of yours in the Service Clinic quite a while ago, I added snore capacitance to the filters of a TV set to get out a 120 -Hz humbar in the picture. I had to add 400 µF, but I got rid of it. Isn't this too much ?-A.D., N.J. Not if you got rid of the hum! There's no such thing as too much capacitance in a filter circuit; at least not if you still have hum -bars which are a definite indication that there isn't enough capacitance in the circuit. Ifs possible that if you took ev- ery one of the original capacitors out of the circuit and checked them very RADIO -ELECTRONICS www.americanradiohistory.com Clinic carefully you'd find high power- factor in several of them. This reduces the "filtering efficiency" of the unit. However, if the operation is satisfactory with the added capacitance, I'd take it. Open Transistor? I'm studying TV repair. The other day I replaced an open transistor in the output of a stereo amplifier. It wouldn't work! Collector voltage read normal. I took the new transistor out and it tests ok! -R. G., Tulsa, Okla. Most likely possibility (because it happened to me only the other day!) is a completely bad contact on the lug which makes the collector connection on the output transistor collector! Most of these are bolted in, and any oxide, coating, etc. on the case of the transistor (the collector contact) will keep the solder -lug from making good contact. Test from the case of the transistor instead of the lug. If you can't get any voltage on it, put a good sharp lockwasher between the lug and the case and tighten well, or scrape the case clean at that point. Super Hearing Aid I hare a customer tcho wants to get a mike and amplifier, battery-operated, with a "rifle- type" mike that he can point at the preacher, so he can hear church services. Could I use one of the little cassette tape-recorders, or something like that ? -A. A., Vienna, Va. Doubt if one of those little recorders would have enough gain. Better idea would he to use a small IC amplifier. Motorola has one in their HEP IC booklet, called a "Super High Gain Amplifier." It uses a HEP-580 IC. Should have ample gain to drive a single earphone from any good mike. The whole thing could be mounted in the case from a junked transistor radio, with the batteries, using the original earphone jack. R-E This column is for your service problems-TV, radio, audio or general and industrial electronics. We answer all questions individually by mail, free of charge, and the more interesting ones will be printed here. If you're really stuck, write us. We'll do our best to help you. Don't forget to enclose a stamped, self -addressed envelope. Write: Service Editor, Radio- Electronics, 200 Park Ave. S., New York 10003. DON'T SETTLE FOR A HIT AND MISS IGNITION SYSTEM Install a JUDSON ELECTRONIC MAGNETO It offers the combined advantages of both the standard transistorized and capacitive discharge systems in one simplified patented circuit. Provides better performance, a smoother running engine and keeps your car in tune. Installed in twenty minutes. svnsoiv Write Today for Literature RESEARCH & MFG. CO. CONSHOHOCKEN. PA. 19428 Circle 77 on reader service card GET BETTER TV RECEPTION ELIMINATE SNOW WITH TUN -O -BRITE the heavy duty tuner spray with built -in polishing action ! CHEMTRONICS 1260 Ralph Ave. BROOKLYN, N.Y. 11236 Circle 90 on reader service card MarkTen B .. . the gift for the man who has everything. It's new! It's practical! It's differed! Christmas comes but once a year, but car problems continue year round. So why not give the gift that provides continuing pleasure and satisfaction ... the Mark Ten B CD System. Keeping your car in tune is impor- tant to the life of the car. What did your last tune -up cost? More and more, tune -ups are becoming a major maintenance expense, costing $60 and up. Now you can eliminate two out of three tune-ups (that's real savings). Delta's all new Mark Ten B CD System is made especially for foreign cars and modern American engines suffering from smog control devices, rough idle and poor fuel mix. The system is completely sealed, with handy switch for instant conversion. Quick installation -no rewiring. The Mark Ten B actually pays for itself in dollars saved. You may even want to give yourself a Mark Ten B Christmas. Order today! "Delta Products, One Of America's Finest Names In Electronics" Mark Ten B Only $5995 ppd. (12v neg only) Standard Mark Ten $4495 DP 70 -221 c4" DELTA PRODUCTS, INC. P.O. Box 1147 RE / Grand Junction, Colo. (303) 242-9000 Please send me literature immediately: Enclosed is $ . Ship ppd. Ship C.O.D. Please send: -Mark Ten B@ $59.95 _6 - Standard Mark Ten (Assembled) @ $44.95 Volt: Neg. Ground Only Positive Ground -12 Volt: Specify Negative Ground Standard Mark Ten (Deltakit,) @ $29.95 (12 Volt Positive Or Negative Ground Only) Car Year Make Name Address LCity/State lip Circle 74 on reader service card www.americanradiohistory.com Find the trouble faster... SERVICE AIDS P.,,T AL. FAST WAYS TO RESTORE A RASTER with Triad's latest Service Aid No. 5: "Fast Ways to Restore a Raster." Here's an easy -to -read 8 -page Service Aid which will get you to the heart of the trouble faster than any treatise of its type for professional TV servicemen. Uses a direct and comprehensive approach to horizontal and high voltage problems. Helps you find the trouble and tells you how to correct it. Has many service tips that will prevent call- backs. Includes valuable information on - both color and black- and -white TV. Write for your copy today and - also for Service Aid No. 4 on "Under- standing Related Circuits Multiple Trouble." Previous Service Aids (or PTM's) are either being revised or have been updated into No. 5. See your Triad Distributor for all your replacement transformer needs, and get the Triad Catalog & Replacement Guide while you're at it. Triad Distributor Division, 305 North Briant Street, Huntington, Ind. 46750. NEW TRIAD 1971/72 CATALOG AND REPLACEMENT GUIDE triad Distributor Division 01 Litton Industries CB Circle 78 on reader service card 86 4 CHANNEL STEREO (continued from page 35) cities-Boston, New York and San Francisco -FM stations have used three different pairing and placement techniques, each for its own good reasons. In Boston the four microphones, which carried live concerts of the Bos- ton Symphony Orchestra, were ranged more as a "curtain of sound" than as a true quad pickup. One station used the left and right mikes placed at the left half of the stage, while the other took left and right channels for the right half of the stage. This way, both stations had a two-channel stereo signal of sorts, even though the total quad effect lacked true surround sound placement, directivity and separation. The stations involved were educational station WGBH-FM and commercial WCRB -FM. In New York, FM Guide Publisher Harry Maynard introduced quad on his weekly show for stereo buffs, "`Men of High Fidelity." New York City-owned WNYC -FM carried the front left and right channels and Columbia University station WKCR carried the rear two channels. Understandably, the WKCR signal left something to be desired for the majority of listeners who couldn't set up two complete FM stereo systems in their living rooms. But WNYC -FM did provide a full two-channel (and mono) signal for conventional listening setups. This program and its successors were rebroadcast weekday afternoons so stereo dealers could demonstrate quad in their showrooms. In San Francisco, a one-shot broadcast by Pacifica station KPFA and Metromedia's KSAN carried left front and rear on one station; right front and rear on the other. The thinking here was that the stereo dealer could most easily arrange two stereo consoles along opposite walls of his store. Actually, it looks like an ideal arrangement to keep either station from gaining a competitive edge during the experimental quadcast. Later, the Bay Area quadcast gauntlet was picked up by KLOL and KRON, both commercial stations, who interestingly use the same split as in the KPFA /KSAN quadcasts. The Chicago and Cleveland areas are next on the list, and one program packaging company is selling a single syndicated one -hour quad concert by the Boston Symphony Orchestra. The quad disc is the biggest question mark of all. There are private inventors and engineers with huge labo- ratories all bent on a single quest-the single -groove quad disc. They're convinced it's possible, just as they were convinced in 1956 that a true twochannel program could be put into a World's Number One Trusted Name Brand "N°OISE" TECHNICIANS' FIRST CHOICE OVER CHEAPER SUBSTITUTES! VOLUME CONTROL & CONTACT RESTORER TUNER-TONIC with PERMA-FILM EC-44 FOR ELECTRICAL CONTACTS TAPE -RECO HEAD CLEANER FRIGID-AIR CIRCUIT COOLER All Guaranteed Non -Flammable, No Carbon Tet, Non -Toxic, Non Drift Tuner Cleaner And Guaranteed Not To Affect Plastics. The Only Brand Perfect For Color TV and Black & White FREE extender assembly for pinpoint application supplied with ALL NO -NOISE PRODUCTS. Electronic Chemical Corp. 813 Communipaw Ave. /Jersey City, N. J. 01304 Circle 79 on reader service card Build this magnificent Schober Theatre Organ for only * 9730! Includes finished walnut console. Ampliter, speaker system, optional accessories extra. Only $1256 If you build your own console. You couldn't touch an organ less than $3500 -and there like this in a store for hasn't been a musical instrument with this vast variety of genuine Theatre Organ voices since the days of the silent movies! If you've dreamed of the grandeur of authentic big-or- -kit gan sound in your own home, you won't find a more satisfying instrument anywhere or no kit. You can learn to play It. And you can build it, from Schober Kits, world famous for ease of assembly without the slightest knowledge of electronics or music, for design up, and -above aalln-dfoprarttshequhaliigtyhefrsotmprtaheisegrofruonmd musicians everywhere. Send right now for your copy of the full-color Schober catalog, containing specifications of the five - Schober Organ models, beginning at $499.50. No charge, no obligation but lots of food for a healthy musical appetite! ciGlOrgan The Corp., Dept. RE.83 43 West 61st Street, New York, N.Y. 10023 Please send me Schober Organ free 7 -inch "sample" record. Catalog and Enclosed record of please find $1.00 for Schober Organ music. 12-inch L.P NAME ADDRESS CITY STATE 71P Circle 80 on reader service card RADIO -ELECTRONICS www.americanradiohistory.com single record groove. They may be right. But there are just as many skep- tics around now for quad as there were for stereo in 1956. They may be right. So far, whatever results that have been publicly demonstrated have left much to be desired. The long-awaited public unveiling of Peter Scheiber's disc came at the March AES meeting before standing-room-only crowd in RCA's spanking-new recording stu- dios. Those of us who heard it came away convinced that the Schieber disc just doesn't have what it takes for true quad. Scheiber's technique is supposed to condense quad's four channels into two stereo channels that are fully compatible with all conventional types of playback equipment. A master disc would be cut with the same Westrex stereo cutting head, and the record would be played back with any con- ventional stereo cartridge-even the cheapest crystal types. The output sig- nal would be processed through a black box (patent applied for) deco- der which would have four -channel output to feed a quad amplifier (or two stereo amplifiers if you will). The same technique would com- press quad into two ordinary stereo tracks on tape or into an FM station's conventional two -channel FM stereo broadcast. The secret of all playback would be in the little black box deco- der. Equipment without the decoder would simply play back a normal two - channel program. The whole idea sounds especially captivating since its compatibility would eliminate a lot of headaches and retrofitting now seen as needed for quad playback. The system, alas, isn't all it's cracked up to be. In Scheiber's own words, it's a "psycho-acoustic effect." Purists take note: it's a psycho- acous- tic effect; not the real thing. But you don't have to be a purist to be con- vinced of the system's shortcomings. What it does is place the appar- ent sound source at any two selected speakers out of the four at a given instant, with some other assorted sounds coming from the other two, with lots of spillover. The Scheiber system is perhaps best described as "21/2 channels of stereo." It's defi- nitely not true quad. So the search goes on. Familiar names are in the fray again. Jerry Minter is back with his multiplexing technique. Columbia Records is work- ing on something that's still a closely guarded secret. And there are others, names that may someday be house- hold words, or simply inventors that won't quite make the grade. In the meantime, the smart money's on tape and FM. R -E OCTOBER 1970 87 NEW SEMICONDUCTORS MOS IC FOR TV SYNC The HSUB0525 is the first MOS IC developed for digitally controlling the horizontal and vertical deflection in TV receivers. It takes a 1.08 -MHz crystal oscillator signal and divides the frequency down to produce accurate and stable horizontal, vertical and composite blanking pulses while eliminating variable resistors and potentiometers in the control circuitry of the horizontal and vertical generators. The IC is particularly suited to cable or closed- circuit TV and TV test instruments such as bar and raster generators, as well as for CRT character displays. It is compatible with commerical TV sync systems when used in conjunction with proper vertical sync separators. This new Hughes IC is housed in a standard 10 -lead TO -5 package and is priced at $15.00 each in 100-or-more lots. For further information, contact Hughes MOS Div., 500 Superior Ave., Newport Beach, Calif. R-E anniversaCy 468 PAGES; Your 1st Guide To Everything in Electronics tceemiPBvSsehltaeroscrtkoeTgoora/oaBHnlposdi-hoFaykWinsdEhCaqiTtnoeuedmi/spCptPmooEalenorqnetrsutnitpTsmelHeenavmtisMiouanEsnsiddcuaCcl aBPtiIonGonsleicatarelur maanendnPdtOusbFplitiraciecnadAlMdEoAdqrnmeuitspiopslrmifiSeeRyrness-tPlus Thousands of Additional Items Mail This Coupon Today For Your 1971 Catalog No. 710 Send For Your Free 1971 Lafayette Catalog Today! LAFAYETTE Radio ELECTRONICS Dept. 17100 r P. 0. Box 10, Syosset, L. L, N. Y. 11791 I Send Me the Free Lafayette Golden Jubilee 1971 Catalog 710 mi 1 Name 17100 Address City State Zip (Please include your zip code) -1 Circle 81 on reader service card www.americanradiohistory.com MCEANRTKEERT ELECTRONICS TUBE sale. To 90% off all brands. Laboratory type CCTV oscilloscopes, generators, tubes testers. 85% off. Model PD -160 $700.00; you pay $105.00. Mail order only. Free list. J. Knight TV, 612 Gaines Ave., Hot Springs, Ark. 71901 RBEraCnEdIsV-IBNGigg&esIntduDsistrciaolunTtusb. esT,ecThrnaincisainstso,rsH. oAbl-l byists, Experimenters- Request FREE Giant Catalog and SAVE! ZALYTRON, 469 Jericho Turnpike, Mineola, N.Y. 11501 INTEGRATED CIRCUIT KITS-Free Catalog. FRAZIER & ASSOCIATES, 3809 Surfwood Road, Malibu, Calif. 90265. eColseOccNitllrVooEsnRcicoTpaene. yxOptneelrlyieevnmisciieonnorntoechcseaesnnsgaseristyiv. reeqbIluilguir-sestdcra.reteNedno plans $2.00. RELCO -A25, Box 10563, Houston, Texas 77018 B & K, Sencor test equipment, discount prices, Free catalog and price sheet. FORDHAM RADIO, 265 East 149th Street, Bronx, NY 10451 COLOR Organ Kits $3.25 to $7.50. Power Supplies $2.75. Catalog. MURPHY, 204 Roslyn Ave., Carle Place, N.Y. 11514 RADIO and TV Tubes 33¢ each. One year guaranteed. Plus many unusual electronic bar- 4217-E Univer- sity, sS nfeDi go,aCalifornaN92 DISCHARGE Ignition, Photoflash. Free catalog parts, kits. TRANSPARK, Carlisle, Mass. 01741 prices. Foreign-American. Obsolete, receiving, special purpose, transmitting tubes. Send for tube, parts catalog. UNITED RADIO COMPANY, 56 -R Ferry St, Newark, N.J. 07105 JAPANESE NEW PRODUCTS MONTHLY! $1.00 Refundable. DEERE. 10639 Riverside, North Hollywood, Calif. 91602 EXPERIMENTERS, Radio control enthusiasts, Bramco five tone reed relays. Standard frequencies. Brand new, boxed $4.00 each. E.S.P., 8913 Cermak Rd., N. Riverside, III. 60546 - AUDIO HI -FI CASSETTES CASH IN ON round market. Send for a tremondous lowest pricing All -year and de- tails. Include $1.00 for 2 cassettes samples. DICTATION PRODUCTS, P.O. Box DPK, Hallan- dale, Fla. 33009 FM BACKGROUND MUSIC ADAPTER. Compact line- powered MUSICON MX -7 plugs into any FM Tuner or Receiver. Optimized dlsign guarantees 5 years of commercial -free music without adjustments! Works with your equipment or we refund. Send stamped self- addressed envelope for SCA stations in your area. Lowest price ever . . . $35 postpaid from K -LAB, Box 572R, S- Norwalk, Conn. 06856 -7" -2 SsmpTaeEneRudEfsaO-cptuarueTsrA-eP5E0cotTonRtrAo15Nl-,Sm00P0aOdRHeTz for -with reel famous rec /play and erase heads. Without case. Send M.O. or check for $19.50 to STEREO CENTER, 218 Co- lumbia St., Utica, N.Y. 13502. $2.50 for pre - paid shipping and insurance. ... CLASSIFIED COMMERCIAL RATE (for firms or individuals offering commercial products or services). 70¢ per word minimum 10 words. NON -COMMERCIAL RATE (for individuals who want to buy or sell personal items) 30¢ per word . no minimum. FIRST WORD and NAME set in bold caps at no extra charge. Additional bold face at 10¢ per word. Payment must accompany all ads except those placed by accredited advertising agencies. 10% discount on 12 consecutive insertions, if paid in advance. Misleading or objectionable ads not accepted. Copy for December issue must reach us before Oct. 5. ADVERTISING INDEX RADIO -ELECTRONICS does not assume responsibility for any errors which may appear in the index below. READER SERVICE CARD NO. Allied Radio Corp. PAGE 75.. 75 Blulyne Elec. Corp. 84 67 Brooks Radio & TV Corp. 76 -7 69 Burstein -Applebee Co. 82 84 Castle TV Tuner Service Cover III 10 Channel Master 15 73 Chemtronics 83 90 Chemtronics 85 6 Cherry Electrical Products Corp. 12 19 Cleveland Institute of Electronics 28 -31 82 Compusad, Inc. 92 CREI, Home Study Division McGraw-Hill Book Co. of . 65-6 83 Crystek, Division of Whitehall Electronics 92 62 Delta Electronics Co. 74 Delta Products Inc. 72 84, 85 79 Electronic Chemical Corp. 86 EMC, Electronic Measurement Corp. 74 72 Enterprise Development Corp. 83 1 (Garrard) British Industries Corp. Cover II 2 Grantham School of Electronics 1 20 Heald Engineering College 68 Heath Co. 70 78 -81 85 International Crystal Mfg. Co. .. Cover IV 77 Judson Research & Mfg. Co. 85 81 Lafayette Radio Electronics 87 Lakeside Industries 92 64 Leader Instrument Corp. 74 8 Lechtrotech, Inc. 14 63 LubraClean Co. 72 3 Mallory Distributor Products Co..... 5 5 Master Appliance Co. 12 61 McGraw-Hill Book Co. 71 65 Mosley Electronics, Inc. 76 Music Associated 92 National Radio Institute National Technical Schools 8 -11 18-21 76 Olson Electronics, Inc. 84 71 Precision Electronics 83 12 Precision Tuner Service 17 CLASSIFIED ADVERTISING ORDER FORM 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 13 Raytheon Co. RCA Institutes RCA Parts & Accessories 66 Rye Industries, Inc. 70 S & A Electronics 18 Sams & Co., Howard W. 80 Schober Organ Co. 11 Sencore 14 Shure Bros., Inc. 9 Sonar Radio Corp. 4 Sony Corp. of America 17 Spectrum Products Co. Sylvania 7 TEAC Corp. of America 78 Triad Distribution Division of Litton Inds. 16 United Technical Institute, Division of Career Academy 15 Xcelite Inc. 22 54-57 73 77 82 27 86 16 23 14 7 26 32 13 86 25 24 31 32 33 34 35 =$- ff @ .30 Non -Commercial Rates) No. of Words 1. @ .70 Commercial Rate No. of Words in bold caps @ .10 =$- MAME ADDRESS Tetal Enclosed $ Insert-Wings) Starting with Issue Payment must ac- cleomspsany order un- placed through accred - iced advertising agency 28 CITY STATE ZIP SIGNATURE MAIL TO: RADIO- ELECTRONICS, CLASSIFIED AD DEPT., 200 PARK AVE. SOUTH, NEW YORK, N.Y. 10003 88 MARKET CENTER 88 Edmund Scientific Co. Fair Radio Sales Mongram Publishing Co. 87 Park Electronic Products 89 Polypaks 86 Solid State Sales Supreme Publications Surplus Center 88-91 SCHOOL DIRECTORY 89 Edison Technical College Tri-State College Valparaiso Technical Institute RADIO -ELECTRONICS www.americanradiohistory.com It's The Biggest! It's The Most Popular PENNY SALE IN THE INDUSTRY! CENT 99c Type Description Case 900 for 900" 903 903 904" " 908 909 910 " 912 913 914/921 925 " 926 Buffer F Dual Buffer F Dual 3 input gate Dual 3 input gate Dual half adder Full adder 5 F N 5 Buffer 5 Dual two input gate Half adder 5 5 Shift register 5 Dual 2 input gate Dual 2 in. w /expand Hi speed 923 5 F F ' "' Code: 2 identical ICs in 1 pak. DTL, Type Description 960 Dual buffer Case 5 Each 2 $1.01 923/940 J -K flip flop 5 WC210 "" WC2I5 WC226 "" WC227 "" WC261 WC266 "" SG -43 5G -123 5G -163 NE -124 2 -3 in line driver J -K flip flop Triple 3 In. gate 10 In. Diode expand Dual 4 In. gate Quad 2 input gate Dual 3 In. gate Expandable 8 In. gate Triple 2 In. bus driver R-S -T binary F F II F F F F N N N SG- Sylvania; NEa Signetic, vï/YgY Sprague. WC- Westinghouse; otherwise RTL. F =flat pak; N =dual inline; 5 =T0-5 case. TEXAS- NATIONAL DTL TTL ICs! Type Description SN7350F * Quad 2 input gate . SN7400N Quad 2 input gate SN7404N Hex inverter D SN7430F 8 Ihput Nand gate SN7440F Dual 4 In. Nand buffer SN7441 N BCD -to- Decimal decoder -drvr 0 SN7442N BCD -to- Decimal decoder SN7470F J -K flip flop SN7472N J -K master flip flop D SN7473N Dual J -K master slave flip flop SN7474N Dual 'D' type edge triggered flip flop ......... SN7475N Quad bi-stable latch . SN7490N Decade counter 0 SN7492N Divide by 12 counter SN7493N 4 Bit binary counter SN7302F * Duel J-K flip flop with preset SN7304* Dual J-K flip flop with preset & clear " DTL, others TTL. F= flat pak. N =dual inlinc Sale 99 ,99 1.19 ,99 .99 5.95 5.95 99 1.19 1.49 1.49 3 95 4.95 4.95 4.95 1 .29 1.49 IBM 4000 Bit MEMORY core plane, from computer #1401. only $8.50 FALL-CHRISTMAS LIMELITERS 23---7--ING -15 El 2 -FT. finished fiber 709 OP AMPlifer optic lite pipe 2 UNCIJHUANNCNTEILONplatsratincsFisettosrs2N23N8418991Texas 1 MOS FET P channel 2N4353 5 CLAIREX photo elec cella pancake 810-1-T1RAIGAMMGPEPR180d00io00dePPsIVIVforresciSlt,icfirreaer,csTtifriiearcas 4 2 NIXIE tube driver transistors -AMP 200 PRV acre 2N4409 . . 2-WATT G-E PA237 audio amp 1 -WATT WESTinghouse 1 -AMP Triac 200 WC334 PRY audio amp NE161J One shot multivlbrator Signetic 2 MICRO reed switches 1'r long 1W0E0STTirnagnhsoisutsoerspoasssittivenpnv-oplnt pr-epgwurla-ntoor test $1.00 $1 49 $1.19 .$1.19 $1.00 $1.19 $1.00 $1 19 $1.19 $1.00 $7.19 $3.98 $1.49 $1.49 $1.79 $1.00 $1.98 0 to .10 VDC $1,19 10C Catalog on Fiber Optics, 'ICs', Semis, Parts Terms: Phone Retail: O2a1r1dddeArslpb:oiosWtnaa,gkeSe.tf.i,RelWadt,eadkM:eafisnesel.dt,(36M01,a7s)cso.2d4's5-3285259, POLY PAKS FAIRCHILD 741 CAMP'only $2.50 /Same as 709 with frequency compensation, P.O. BOX 942R LYNNFIELD, MASS 01940 Circle 89 on r 'acier service card AMAZING OFFER 1969 RADIO & TV SERVICE DATA Your hest, complete source for all needed RADIO and TV diagrams and helpful servicing data. Most amazing values. Only $2.50, $3. $4, per giant volume. Cover all important makes, models of all periods. Use this en- -, tire ad as your no-risk order form. NO -RISK ORDER COUPON TELEVISION SERVICE MANUALS w$srse4eeinrpt.sdiSan.piucgerehpsCr-nar.beontolimamgrLaereeorpgsdwle,eaTetdeVdasavntinaedmcnpgrituadrrriisaacnocelmuuuemiabdstmsll.,ese,anFn-wtpaauaaaracaelsgvtll.oeebrynfyseooCecsruehtdmhrdeeafseomcto,dakrradtvefoviaaconorlssliltgu.pftaoemnrgOrrameme,cnsse.tle,yincatwaps$aril3elfonyardtcaeutnTadscdVl,,.l D A1NN1119999de6e6661dww569iti1BTTT1o9VVV9n-77W,.0a0Ml$B$3aCT31-.n.9VWOEu,L2aOl$T,T4RV.V$,3,T1.$9$E463.14L.9E6T8VVI,TASVd$rIO;,3d11.9iN9t$6Ei64o0a9.nMrTCalDyValOnL111u1M999O9a6666alR532.7nuoTTTTTanVVVVVll,,,.y,. $4. $4. $4. $3. $3. $3. $3. 91M95a58s5ttTeTVrVaI.nMdM$ae3anx. nSutoala, ll$31T.9V$534.&TVRA,add$ido3.itMioannaulal1s199,5571250TT.VV,. $3. $3. RADIO DIAGRAM MANUALS 50 cFmps8rroea-tMrra1impdniG-tn/aiiAt2bocegeiMsirstdinsn,,ax.tgthtoi,aeoCab1slnnolo1epdhasv"r,ri,enendlerowastaesw,uabdet.trroe-ovapvudenooVrtrsisllcoydteai1eatlst-ulh9sdgittgmoi.0ienmnrregmaeLpsddaareysipgaronoa;geottuaresrem,t,aaflamsbaelcdbnlcaaehuiittcygaessyah,-,,lplnseeaenrdaddfisrooismm, plsirfteeycreeaonl,lt 1966, El 1960, 1953, O 1942, 0 1965, 1964, 1959, El 1958. 1952, 1941, 1951, 1940, E 1963, 1956, 1950, 1926-38. 1962, 1961, 1955, 1954, 1948. 1946. EACH, $2.50 1965 Also Auto Radios, New 1967 -1969 Simplified Servicing. combined Radio Volume, $1.50 $4.00. SUPREME PUBLICATIONS 1760 Balsam Road, Highland Park, ILL., 60035 Rush today nn -risk order enclosing full TV and Radio manuals checked in form of this ad. Send postpaid. I am price. Satisfaction guaranteed. Name: Address: City: State: SCHOOL INTEGRATED CIRCUITS RECTIFIERS lJ SEMICONDUCTORS TRIACS DIRECTORY EDISON With TECIaIConfd TwmS4IEEOnn6ceiinle2ttsheclehgee9soccnirvioutnoirsniVlpcesosnigaoav.ien,onnteriincifoAnNisdEnpaNgeaianpDnuntTldridyTIcTooeSseueTvnceO.scehcraVBthadnNhrloIAynoin.nc-olAfrooioaroTVnllsgorortrgaesEiyggolneo.dVyCyncui;eattHNite(GatleAeudtNErdtisyrao-alIssrednCTniobucapseyAcat(rlo.rLcoiltLoa,feohgItWtmsshsnreTaeieCrrcmDAiaScitOaiAnsdeheninngLegcacserLcnfeeoIdlrEaineeceernGsaimd1dn)lICEi9anEti4anDTCnl5ted7.egAr-D2cc-aEtRethrw9fCormnEtn1ainkoinM4agcismic0nga)ni).s3-d-l;; distinguished graduates hopthuolartledceeUmi.ymSee.panortsPr.trraeoDn4JAvcfueet0eodnds0etrmsedisnc-.,i.iaaogsctsMnierniFSaedooeeolndleypuesfcr-tra.i,ra-onaqcmrgtuiueFeipnlaoantudytrrntsot.eide.ctdaCraMmltaAiontacycdcagooencelostaarmttgeagrs,cdge. aleimatpErewbeeednswenrr.t.mirtetiterhipSAtspomJprsaoDepatnusdfirlrel.ote,esrvtgecchteMralntraeodoncasereudrsc.gefihnootsho,grf.. TRI -STATE COLLEGE 24100 College Avenue, Angola, Indiana 46703 GET INTO ELECTRONICS tItVnoer.cay'Thd.cn.vlo.iacEmniacltmenercadsuti,rnnroaiicnnfdiaegiactlridsoenlEseesnan.idggnsiignntueeheietedoarruesitnod.msgueatcpimoTcenee.ilcasscocbshauonliereoaastls-s-, both available. Technology Aeeociate Inc 29 peSscrleeohpvcoteto.rd,ol .Hng.iFrcSaG.esdrbauw.daaiutltehsaDoteomosrrmaobjesoitnqa,riunciaavoclbalamllmeep.nbaptrnu.aisenGC..scI.ah.teSHa,ltioaaggporht-.f VALPARAISO TECHNICAL INSTITUTE Dept. C. Valparaiso. Indiana 46383 PRY 100 200 300 400 500 TRIACS I lA I 10A I .50 1 1.00 I .80 1 1.40 I 1.10 1 1.80 I 1.40 I 2.20 I 1.75 I 3.00 7A SCR's) 6 sets /$1.00 144x28 stud (30 amp. rectifiers, 20 amps SCR's) 4 sets /$1.00 MRTL IC's 908 FULL ADDER .75 912 HALF ADDER .50 913 REGISTER .50 940 1K FLIP FLOP .50 ER900 TRIGGER DIODES. These biodirectional trigger diodes are one of the best and cheapest methods to trigger SCR's and triacs 3/$1.00 UNIJUNCTIONS! Similar to 2N2419. RBB of 5 -7 stand off ratio of .6 and Ip of 12 with data sheet 5.80 D N- CHANNEL FET'S TO-18 plastic units, low noise, low leakage, 25 volts source to gate, 50 ma gate current Gain to 9000 µmho's. $ .60 2N4303. P channel FET with a Q ms of 2000 µohms $.95 MM 2260. An NPN TO -5 silicon unit used for video output circuits in transistorized TV's, with a gain of 35 and Vcb of 75 $ .75 MOUNTING HARDWARE KITS. These kits are used to mount our SCR's Zeners and Rectifiers etc. 6x32 stud (3, 12 amp rectifiers, TTL IC SERIES DECADE DIVIDER RF 112 Dual 1K Flip Flop MC 415 1K Flip Flop MC 400 Dual 4 input NAND /NOR gate 4 Bit Storage Register 9301 MSI ONE -OF-TEN DECODER $3.95 1.25 .85 .70 1.25 2.95 Silicon Power Rectifiers PRY 3A 100 .09 200 .16 400 .20 600 .30 800 .40 1000 .50 12A 1 30A .24 1 .50 .35 .80 I .45 1 1.20 .70 1.50 1 .85 I 1.80 1.10 1 2.20 Terms: FOB Cambridge, Mass. Send check or Money Order. Include Postage. Average Wt. per package 1/2 lb. No. C.O.D.'s. Minimum Order $3.00 FIBRE OPTICS 1/32" 2.5 mil. fibers in PVC packet. $ .33 /ft. COMPLETE LIGHT GUIDE BUNDLE consisting of an 11" length of 1/32" dia. fiber optics with bound ends. $2.00 ea. Controlled Avalanche or Epoxy Rectifiers 1 AMP. PRV 100 1 .07 200 ( .09 400 .11 I PRY 600 1 .1fi_ 800 1 .20 1000 I -30 Silicon Control Rectifiers PRY I 3A I 7A 20A 70A I 50 .30 .35 .70 1 1 100 1.40 I .55 200 .60 .80 I I 300 1.80 1.00 1 1.00 1 1.30 1 1.70 1 4.00 8.00 400 1.00 11.30 I 2.10 1 12.00 50011.2511.60 2.50 600 1.50 1.90 13.00 116.00 I BIGGER AND BETTER BARGAINS. Send for our latest catalog featuring Transistors and Rectifiers; 325 Elm St., Cambridge, Mass. TATE ALES Somerville, Mass. 02143 PA Tel. (617) 547 -4005 Circle 86 on reader service card www.americanradiohistory.com MARKET CENTER UNSATISFACTORY "live" recordings? Inexpensive new products for improved microphone Fidelity and flexibility are available. Write RUSSOUND, Inc. Dept. 3, Box 1015, Framingham, Mass. 01701 NEW BSR record changers; $13.00. McDonald 300-18.00; 400-$20.00; 500-$25.00; AM /FM component system-$50.00. DAVIS, Dept. RE, 2737 Third Ave., Bronx, N.Y. 10451 7A4M1PPLIFTIEERXASS-$2.I0N0STpRluUsMEpoNsTtageO. PBEARLALTIEOLNEACL- TRONICS, Box 68, South Willington, Conn. 06265 R-3E,N0T004-tradcikffeorpeennt-frreeeletapebsro-cahlulrem. ajoSrTlEaRbIeOls- PARTI, 55 St. James Drive, Santa Rosa, Calif. 95401 SAVE over 331/3 on a pair of one of the World's Best Speaker Systems. Shipped Direct to you from factory. Try them in your home for thirty days. KGLL, INC. Water Street, Lewiston, Maine 04240 -plus- MEMORIZE, Study: "1970 Test-Answers" for FCC First and Second Class License. "Self -Study Ability Test." Proven. $5.00. COMMAND, Box 26348 -E, San Francisco, Calif. 94126 ELECTRONICS Engineering. Day or evening classes. Bachelor of Science Program evenings. Associate in Science Program day or night. If you are married or if you must work for a living while obtaining your education, this is the college for you. Approved for Veterans. WESTERN STATES COLLEGE OF ENGINEERING, 970 West Manchester Avenue, Inglewood, Calif. 90301 FCC First Class license in six weeks: Nation's highest success rate -approved for Veterans Training. Write, ELKINS INSTITUTE, 2603 E Inwood Road, Dallas, Texas 75235 INVENTIONS & PATENTS EDUCATION/ INSTRUCTION TV TUNER REPAIRS-Complete Course Details, 12 Repair Tricks, Many Plans, Two Lessons, all for $1. Refundable. FRANK BOCEK, Box 3236 (Enterprise), Redding, Calif. 96001 INVENTORS: Protect ydur ideas! Free "Recommended Procedure ". WASHINGTON INVENTORS SERVICE. 422X Washington Building, Washington, D.C. 20005 INVENTIONS Wanted. Patented; Unpatented. GLOBAL MARKETING, 2420-AE 77th Ave., Oakland, Calif. 94605 "HOW TO INCREASE TRANSISTOR RADIO REPAIR PROFIT.". Write X T R, Box 1556, Las FREE "Directory of 500 Corporations Seeking New Products ". For information regarding de- Vegas, Nev. 89101 velopment, sale, licensing of your pat- BACK ISSUES WANTED of the following magazines: Television, Television News, Short Wave Craft, Short Wave and Television, Radio and Television, Radio News. Also other magazines on the same subjects. Pre 1950 only. Quote exact dates, titles and prices in first letter. Monogram Publications, Inc., 21839 So. Avalon Blvd., Torrance, Ca. 90502 BLUEPRINT TO PROGRESS (continued from page 69) technician can tackle is that of a freelance writer of technical material. This is a highly competitive area, for his material must match or even surpass the standards of writing in the field. Furthermore the subjects he chooses. and the way he handles them must attract the attention of editors. But even with the best of presentation, the market is limited. Unless the writer can produce a terrific amount of good material, he will have a difficult time making a living. He may be able to obtain a contract to do one or more spe- FREE Catalog FINESTVOOV T SURPLUS ELECTRONIC BARGAINS Now B I G G E R a n d -- -- BETTER Than Ever! -MAIL THIS COUPON NOW NAME: ADDRESS CITY: STATE: ZIP: For your FREE copy, fill out coupon and mail. Dept. RE FAIR RADIO SALES 1016 E. EUREKA Box 1105 LIMA, OHIO 45802 cific jobs that will pay well for a short time. One such area is writing technical films; but the competition is fierce and the chances of landing such a job are fairly limited. Requirements for free -lance writing include the ability to plan and write clearly, but even more, an aptitude for recognizing a salable subject and the in- centive and energy to do the research necessary to make an article or book in- teresting and different. There are any number of writing courses at colleges and correspondence schools that will give a technician the basic tools he needs. But he must be ready to serve a long apprenticeship before his material will be regularly requested and paid for. The different positions discussed do not exhuast all the possibilities open to a technician seeking to progress from an hourly to a salary position. They should, however, indicate that the path is defi- nitely not closed. Assuming he has be- gun his education program early to an- ticipate openings, he then should indicate his qualifications to his super- visors and 'his readiness to move into a salaried position. With his technical ex- perience he should hive a decided ad- vantage. R -E 90 ented /unpatented invention. Write: RAYMOND LEE ORGANIZATION, 230-U Park Avenue, New York City 10017 GOVERNMENT SURPLUS DIFFERENT? YOU BET. INDUSTRIAL AND GOVERNMENT ELECTRONIC SURPLUS AT LOWEST TPRROICNEISC.S,GEBTOXOUR171L2A7T, ESPTORLTISLATNDN,OWO!RESGTAORN97217. JEEPS Typically from $53.90. $78.40. Boats, Typewriters, . Trucks From Airplanes, Mul- timeters, Oscilloscopes, tronics Equipment. Wide Transceivers, ElecVariety, Condition. 100,000 Bid Bargains Direct From Government Nationwide. Complete Sales Directory and Sur- plus Catalog $1.00 (Deductible First $10.00 Order). SURPLUS SERVICE, Box 820 -REL, Hol- land, Michigan 49423 WANTED QUICK CASH . . . for Electronic EQUIPMENT, COMPONENTS, unused BARRY, 512 Broadway, 212 WALKER 5-7000 TUBES. Send list now! New York, N.Y. 10012, GENERAL SvsSOeiPOnhlfEyiU-olAaNK4dDc4dEo3rRev1Pes0RsrRiOenEdgDC,,UOCNhsTtIaaNSrmdG, w,p2ae6rd2reeA.pelaCFncvroeaermnlozpeprneiPct:leagcCreliiR,lslEtAAckslTroeoItVnhndE,, - PEP'S Dollar Sale Si Money Back guarantee $1 I Amp Silicon Rectifier choice of package Bullet- Miniature Glass- Metal 5-800V units $1.00 la 4 -1000V units $1.00 3.1200V units $1.00 7 AMP SCR El 4-50V units $1.00 3.100V 2 -200V 1 -500V Cl 1 -800V units units unit unit $1.00 $1.00 $1.00 $1.50 20 AMP SCR 3 AMP Epoxy Package C7 2 -50V units $1.00 10.100V units $1.00 1 -300V unit $1.50 S -400V units $1.00 Gen Purpose PNP 2-1000V units $1.00 Germ Transistor Similar to 2N404 TRIALS 8 For $1.00 PVR 10A 100 1.00 2001.40 300 1.90 _400 2.30_ 500 2.75 ZENER DIODES 3 Watt 10 Volts 3 units $1.00 ZENER DIODES 1 Watt 1 EA 4V- 6V- 8V -10V 4 units $1.00 GERM GLASS DIODES SILICON STUD MOUNT 007 GEN PURPOSE 20 AMP 20 Units $1.00 3-100V units $1.00 Replaces 1N -34 1N -60 1 -1000V unit $1.50 1N-64 1N-295 I.C. SUMMER SPECIAL 14 Lead Dual In -Line Pkg. Perform same function as 700 series -5 Master Slave Flip Flop 75¢ @ -$3.00 -5 Quad 2 Input Nand Gate 75¢ @ -$3.00 16 Bit Memory Ce1l-$4.25 14 Lead Dual In-Line Pkg. CIRCUIT BOARD COLOSSAL -7 - 3 different groupings to choose from Typical samples below A) 200 diodes transistors -over 50 resistors complete with board! B) 32 transistors-over 100 resistors-capacitors- -- S.C.R.'s over 15 diodes-complete with board! C) 22 -11 lead dual in -line I.C.'s-over Price $1.75 50 diodes capacitors-4 transistors -over 50 resistors complete with board! Price $2.50 FULL WAVE BRIDGES PRV 2Amp I 3Amp 5Amp 10Amp 50V 1.25 I 1.35 1.50 1.70 100V 1.50 I 1.60 1.75 1.95 200V 1.75 I 1.85 2.00 2.20 400V 2.00 2.10 I 2.25 2.45 600V 2.50 I 2.60 2.75 2.95 ELECTRONIC 800V 3.00 I 3.10 3.25 3.45 PARK PRODUCTS P. O. Box 78 N. Salem, N. H. 03073 Tel. (603) 893 -0276 NO SALES TAX WE PAY POSTAGE Circle 87 on render .cervice card RADIO -ELECTRONICS www.americanradiohistory.com U.S. GOV'T ELECTRONIC SURPLUS fcionmeNsptoa,ntimeonontsastllayet xaKpenfronawscintvioe-nW, oGorfoldvtehrFenaimrmeoonruitgsSinuaSrlpUlRuasPcqLeuUlieSscittiCrooEnnNicTcoEusRtn.itosffaenrds IBM COMPUTER POWER SUPPLY e4I'3ao.hdt teIT. E,IbMIi.dea#1egr2aes2nhs-g9i.,p3bs4,r1.r1e) Xt,c-2,m,.'1-IIa1tno't,la1mI r\e,Imeiisaantsa.ri.elasbbe.lawera.cdh1e of Finest regulation 1mnWnmiers, litters. system. Independent I n load IIIIP.,lnage rwtus m,.. 'nil us rations. systei ms. ulatinng rand' by-passed. Ili. noshed, 3a" x i. banished oho 11 tan he without .- ., .1h wocrdanieerr are "regmode ,o ii,, n Ua t1 and 1:" ,, In ". mr145 ,hncrani Inv 'cost Gail over ,Cxtm.oll $24.95 ONCE-IN-A-ILIFETIME SPECIAL - - BURGLAR -FIRE ALARM SYSTEM 29.95 °s, 'sOknyipdsrde.dt(emrmeIamTx)nHEsaebMskanhecets#ulni1raoe1tw1o3.r1a,r55.s2n-s-.1i.'iAm,r1ieg)a1rla.-orfm- Cfiorcenboetxlrluoo3lmr,lD"nu.a(,uar71el13a1a.0ldllbaoitrsntom..r) STANDARD DIAL TELEPHONE ( ITEM me - standard. w m rat v. polished black. lik ondltlm. Use as in n! systems sFullphonnsetsmrtootgoenÑtsherr r r local intercom yc. furnished. wt. 916x- A-4...- ,_ °donut W1i $7.49 Cosa 624.50 STEP -BY -STEP TELEPHONE SWITCH ,De swit(chIT. EGMrea#t1-e9x0p6er1imental pmmei wire telephone dial wall I ...pima,. se1 used with number from O to or woIne. r $6.29 l1ii3gin"htxe,6roc'tox mt5-. I ( 16 ,I 16n i tom on remote Inor 01,,, .1(11 contact $90.00 bank. +pa- Telephoto- dial for use with above switch, OrdlrasI Item Cr00i $1.97 ñ 's'lN °. l ' -. IIPTJ " ' ' MAGNETIC DIGITAL COUNTER(12fo18 -VDC) v '--s.x b (f41 i I uiiii bus TEM 21 -955 ) to count number 1 a t or 1 1 to lanes changingg t le t opened n.- p labo rs- $1.99 mnsr 10th tonaal g eso m net unt ob,reir larn h W il m x 141, TFrore $4.99 TYPICAL BUYS FROM OUR 1970 CATALOGS S ISM $181.11 S 75,115 8211.M 115-Volt DPOT Relays Regulated Transformer, Wide Range 28 -Relay Telephone Panel Gyroscope, Twin Rorer, 24V $1.69 $14.91 $4.39 $9.89 AC PROGRAM TIMING CLOCK 6" -- tffaeocarYttrsua(.trdieImiTrEo-ieoE,VCdMianeicntxc#2s.b41ieg-5hn8moaulu)xirnlctg4iplp.i"epl.ersi7wo( deopp6.nrreokldrAbgmhslhrsai.tomU)mlShk\e'dvs.,tTIrta'-aksmpwpiitt-.cdhac1ionnnga- Cost Gov't Over 330.00 $15.75 l:7"'!,S: 14 -. - SNAP AROUND VOLT -OHM -AMMETER 1m , r the amaogmpoepteos(nrr.asinIn,TRggEeaethaMpsed.psl#ilWam2vniot1ashcl4teicam4sag,4sepesel),ettco-t.e-sp:TMtrheOnrlsel.eeseaaredhscasauu.dnrrr2dsrseloIeínhA"tmaCn.srxdam3ncu"mguperurstxeo.nI5YttnwawÓo".i.pthTvroooebtulstet-t $36.90 aex.mc'p".s5 Oe (ales.) *ai*;: SPECIAL SALE ELECTRICAL ENGINEERING $8.79 Pi. paid $10.79 ou side Uu .S.A. oasB1fivesnantrg-csi(l,hanIlbTelelfuEeII.I.rmMo.iinsug,bkhu#le.IteA,ss.d.dhws.oIo.RiAatonhSttloibm)nunlboitei-lt.eks-t.hdoseOluopnebsruxp'tatmaeo.inmnnbodetinew.rtadeointcfinoihtEinsnnligecCgacreaHltrrdrutiorcimnaageipnl doinEsnEegdnxregvpaniienclcreeeime.lorCewiTnnohdgctueaorslsCsteaotls!naudbLrbasoienerrdcascactoouaolrsrnnyee- RUNNING TIME METER . ..- -- ( ITEM #2188) Ihm,,I Hung hours of electric light, number ofnp electrical u t $4.3q dRtSoleacp9o4,r9d'G9ss"9f.i90nu39ac"hl xhho2ouur!srirs'..e,frrFSeiohgcreiuprrpasti1no1gra5sn,vwdneifhitg.uuhnmtldaM'rcLe1eldbvrtvsho,seletuecp.. I Er gr: =:ç. Cost OVe E29.00 COMPUTER TRANSISTORS ON IBM Computer Quality Units ( #22.928) Unit watt we r transistor aluminum n. k uses. I 1 lb.) t. r on heavy. ribbed, tram experimental $1.99 1st Gov t Over 610.00 (#22-9I5 ) LL power t Unit I.t consists of '2 pots., Ise , al ribbed aluminuonm heat sinks. ideal motor spend control. 14 lbs. I Ins use as cost un,I rner F31An $4.91 HEAT SINKS = G -_ -_ 'F SEND 25e COIN OR STAMPS FOR CATALOGS Ï:°.`.-.- Order Duet? From Ad. Money Rack Guarantee. SURPLUS CENTER DEPT. RE 100 LINCOLN, NE BR. 66501 S J /f E / BARGAINS.. 1000's OF UNUSUAL SCIENTIFIC SPECIAL u NIQUE Cí/LYIoGgHi TING CHROMATIC "MACHINE -GUN" STROBE lied, Green. Blue & White light barrage the eyeballs every 6 seconds with this low -cost mechanical strobe that can run con t !nuously without fear of burning up. Devastating effects over 500 ft. sq. area. Created by rotating color wheel in front I- of 100W 1211v reflector Itoodlumn (incl. elements seem to flash on & off as fcloalsohrisngf,lucptuualstea.tinTgurpnrsodsutoctreboowsi.ndCoownss,-etp-loiosntercso.olpead.rtieWs ailnntuot cabinet. Brass handle. Reg. Stock No. 71.271 EH ---- (9 house X 10 1Xcu6rrve4n"t). ....$28.50 Ppd. 3- CHANNEL COLOR Create unusual trewcnuous variety in & beautiful lighting ORGAN BARGAIN! effects with top -quality this low 1500-Watt -cost unit (5011 W. per channel). Com- ptldIiwngaedirhcieitcety,awtoptcihtlrouhensltigroopihtnlrhstidsce.eirvs.aiCdndasuHneaalllcsoinhpsagepenrinanlfootesetrli ten 150 W. "spots" or 200 ii e1hPa'ohlsuuredgs..esit6c5n-a2ufs4tr."relxiengalhti-r#tlas.Vt.taIcnxUhcse2leus1s/d2ti"onr.egg2m1./2cp) ohmI.tsps.ledt'weTrheeinrsmtraulRcCtsiAeotn-tisIns.gpi-pPlahsotnice Stock No. 71.,223EH $44.50 Ppd. PSYCHEDELIC LIGHTING HANDBOOK oil information packed pages! Fully explitins latest =n psychedelic lighting equipment. techniques. detIlopments. Covers all facets er psychedelic light -show production including strobes, black lights. protectors, crystals. organic slides. mir- rors. color ,nails, polarized Vision. etc. 8162" z Stock No. 9IOOEH color. light 11" looseleaf paper for boxes. Music 3 ring hinder. $3.00 Ppd. LONG -WAVE BLACK LIGHT FIXTURE - Er1 raxactrileymedlyesignveedr,satilloen,g comwave i (32011 -40011 angstroms) black -light (ultraviolet) fixture eluniniltes ha redul shorter ve ,t t, ultraviolet rays. se to identify minerals. fungi, bacteria-check for surface ii flaws, oil and gas leakage- -:^ perfeet for displays with flu- 1!i' cporurasyhoon-npsuc,ollrtnraescrw.eitc1ph0o.-wLdce.,or.nnIneecSti.nWga.dc,pjruel1uss1gtc:a,.ebnlteMII.poaaulpunemtr,inpvueamrint.t.sre. fhlceohcraitaolk.r.,. Stook No, 70,364EH No. 60,I24EH .. REPLACEMENT BULB $12.50 Ppd. $4.75 Ppd, MIRRORED BALLS BOUNCE LIGHT Yesteryear's ballrooms in mirrored lights echo that richochet to the heat of to- day's discotheque. tip to 1,000 lustrous. clear, hand- made gloss mirrors on each ebfafellctsc.reaMteotfoarniztaesdt-itcheligyhctiansgt reflections that blow the mind) Ideal for light show's, displays, restaurants. hotels, Stock Stock Stock No. No. No. 71,066 "EH" 85,180 "EH" 71,065'EH" .......... and (12" (I6' ( 8" modern Diem.) Diam.) Diam.) stores. ....$30.00 ....$75.00 ....$17.50 Ppd. FOB Ppd. NICKEL-CADMIUM BATTERY BARGAIN! Terrific value -slightly used govt surplus. Lightweight 5 cell, 6 volt, 4 Amp -hour battery with almost unlim- ited life. Extremely high current output. Recharges in 1 hour with Edmund kit. Won't deteriorate when left discharged. Minimum main- tenance-fete drops of water per Year. Ruggeri, shock and- vibration reo iatant. nylon case. Delivered partially charged. filled with electrolyte. 31/2' x 2" x fY' 2 lb. Stock Stock No. 70,942EH No. 70,807EH ...(CH(ABRATGTEERRYK) IT).. $15.00 -S 8.00 Ppd Ppd. 3" ASTRONOMICAL TELESCOPE See moon shots. oriel t..,lars. plia:es of Venu, planets cAnl"olusemdiniuaipzm.eedt1e.0rantfod/Il0lo8v0cprrpcinmoawateerrdy. f v mirror. ventilated Equatorial mount with cell. locks on bath axes. Equipped with 60X eyepiece and nmnnl, trio Barlow lens. 2X finder I I, -cope. ": FREE: hardwood "STAR CHART d. ": HEAVENS "HOW TO - - 272 -page "HANDBOOK OF USE YOUR TELESCOPE" Stock No. 85.050EH Stock No. 85,IO5EH Stock No. 85,086EH 4114" 6" $29.95 Ppd. $94,50 FOB $239.50 FOB ROTATING MULTI -COLORED Dazzling colors stream end- LIGHT lessly from ting light. constantly rotaFacetted. trans- parent globe has louvered drum inside with red, green, blue & yellow stars. Bulb heat jects rofltiactkeesri'nbgruinstwahr ichpopinrots- on walls. ccilings. etc. while Individual globe facets pre- r-sateaynrt-oacfpopbnrsroitlaxlin.atlny1t2c"hcoahlnoiggrsihn. g9o-naVrs-bell- shaped base. Surprisingly light. F,asly placers on table, TV, fireplace. or Xmas tree top, Stock No. 71.000EH $7.00 Ppd. PLUG -IN ULTRASONIC ALARM /LIGHTER Silent. economical, easy to - .5.555.. ins hell. No special attach - melts .lust polur geleinctricsioacnkent-etehdeedn. plug lights and/or alarm into it. Activates when it "hears" someone. Besets automatically. Ultra-sensi- tise up Ill :311 ft. Sensitivity control I1019C, t can adjust rillvenielit out pet. for (light light -eliminates fumbling ' oar-lm1ìiZan1j1urWyfreaqlinnuuetndcayfrikn:nise1hs1s0.w-1iI3tdh0eva.bl Ounfioltr-tiiznaAp(at'ir.ntmieern, t.onh-oomffe, office, switch. Stock No. 71,283EH (103," X 31/2" X3!5 ") $69.95 Ppd. 1st QUALITY OPAQUE UNDER $200 Terrific 11110! Top Quality! Projects brilliant. sharp 4 ',z ft. sq. image from s' using up to 55-x5" color. b &vv il- lustrations. Retains all ori- ginal colors, proportions. Enlarges drawings. rains, neaps. et e. Revolutionary peanut -size quartz Halogen lamp (ill hr. life). 20uuun anastigmatic lens Iß -.,. s" F.L.) unique internal re- lit cling t. tea gilt maximum brt htne. s entire field emus. ran be 11,1i Aside down. Turbo a oled, 51/2 et coed. Stock No. 71,272EH (Wt II!S lbs) S80.75 Ppd. GLASS FIBER OPTICS KIT Low-cost kit perfect for exnerinlent jug . Variety of pieces. items. adces,aries. !` .__. l.a c'onlains 0" bundle of uujacketed. 2.5mil fibers sue, va (about 000) ; twelve tie fibers (20mi1); 6" 5 plasft. 0.087" dia. coil of l'VC jacketed (about 200, 2.5mll fibers); 1 ft. light guide w- /polished ends & heat - r(o5d"):IIIta" X 1/2" ilia. X din.) : 110" shrink tips; coherent, hex., 10," rod; heat- shrink material thick, polished face plate; >z' cba glass plate; 52" penlight & adapter (needs 2 A cells, not incl.); piano- convex lens; instr. Stock No. 71.285EH $10.00 Pod. 1st LOW -COST VACUUM PUMP! s, Nothing like ill Top -quality (.4 ,: hand -held pump produces & maintains 25" of vacuum. IIas instant release tab, 1%" diam. stainless gauge (0- 30"). 100's of use- -siphon noxious fluids, evacuate hell Jars and trieve, lifctastsintgesri,lecleoabnje. crtes,- demonstrate Magdeburg - ' hemispheres, bleed fuel 40 lbs. with included much more w/larger cup. "T" lLinieftse. rch(e2e1k/2'leadkisa.me. tc.cuLpi)fts Stook No. 71,301 EH No. 71.300E H (without gauge/ lifter) $12.00 Ppd. 5.50 Ppd. QUICK OCR GO . . . NO -GO" TEST! New hay- io.l wl- I. tim: A Illolley ht 01'14 eq.r- alion hy detecting im- proper characters. lines. spacing before problems occur. Two 27111111 vet idle; with handy, pocket -sized CA.XN. SCIomsizpearaIto&r If\or checking character set Etched with transp. red i i ink. Quickly. easily check character size, shape, skew spacing: line spacing ,C skew: dlr, ke smudges. peaks, valley marlts, English & No. 41,350EH (With Comparator) SIZE 1 RETICLE ONLY- #30,642EH SIZE IV RECTICLE ONLY- /30,643EH tn'btl metric. scales. $34.50 Ppd. $11.00 Ppd. $10.75 Ppd. MAIL COUPON FOR GIANT FREE CATALOG 148 PAGES- 1000's OF BARGAINS Completely new 1971 edition. New items, categories illustrations. Dozens of electri- cal and elerl roulaglletie parts. accessories. Enormous 'election of Astronomical Telescopes. Inique lighting items, Microscopes. BPCoirniusopmcounslafrosrM, caanMtaylaoggwnai"friEerHss,u"rpMluasgne1tlesn, ls.LenMseasi.l EDMUND SCIENTIFIC CO. 300 EDSCORP BUILDING -`DU-E--ll,I - -' BARRINGTON, N.J. 08007 NAME ADDRESS CITY STATE 71P EDMUND SCIENTIFIC CO. 300 EDSCORP BLDG. BARRINGTON, NEW JERSEY 08007 ORDER BY STOCK NUMBER SEND CHECK OR MONEY ORDER MONEY-BACK GUARANTEE OCTOBER 1970 Circle 88 on reader service card 91 www.americanradiohistory.com Rebuild Your Own Picture Tubes? \Vitti Lakeside Industries precision equipment. you can rebuild any picture tube! For complete details, mail coupon. 1 Lakesido Industries I 5234 N. Chicago, CIllal.rk St. 60640 l'hone: 312 -271 -3399 NAME I AD I CITYRES3 I STATE ZIP 1 AMAZING NEW ELECTRONIC COMPUTER NOW AVAILABLE FOR PERSONAL USE - - - AT AN UNPRECEDENTED LOW PRICE! For family fun or individual Instruction, there's nothing quite like the all -new, all solid -state COMPULOGICALTUTOR! Anyone from 8 to 80 can enjoy it while quickly learning digital logic and all other aspects of computer operation. No prior math required. In 20 minutes time, you'll be solving intricate problems just like computer professionals. You'll be entertained and enlightened as you proceed to learn binary numbers, fundamentals of Boolean algebra, logic- building blocks and symbols, truth tables, com- puter circuits, error -detecting logic, storage, programming and ... many other fascinating computer operations. It adds, subtracts, multiplies and divides in millionths of a second. Shows how to apply computer to practical problems of accounting, economics and finance. Perfect for home, school and office. Master assem- bly board equipped with appropriate inputs and outputs, plus all circuits, controls and transistorized logic blocks (modules) re- quired to work hundreds of problems. Big instruction manual simply presents basic computer concepts, with all problems and experiments clearly diagrammed and explained. Desk -size, porta- ble, uses standard flashlight cells (not provided). Order for your. self, your family, and for gifts to youngsters, students, business executives, others. It's new . different . . unique! Only $69 95 post, aid and fully guaranteed. Free full -color brochure. COMPUSAD, INC. 16 Wetmore St. P.O. Box 10 New York Mills, N.Y. 13417 Use coupon below / Please send at once .................. Compulogical Tutor(s) at $69.95, postpaid, with the understanding that if I am not more than satisfied in every way, I may return the Tutor(s) for a full refund. 0 Full remittance enclosed; send postpaid. e- I (Please Add Soles Toe When Applicable) r.. I $10 deposit enclosed; send C.O.D. for balance plus postage and fees. Send free color brochure at no obligation. NAME_ ................._............._............................_................_................_.. ADDRESS....................................................._........._.. CITY STATE . ZIP II Circle 82 on reader service card ENJOY THE "MUSIC ONLY FM PROGRAMS M. A. D. MUSIC ASSOCIATED'S DETECTOR for continuous, commercial -free music with ANY FM tuner or receiver Kit $49.50 Wired $75.00 Cover $4.95 List of FM stations with SCA authorization $1.00. Excellent F.M. Monaural Tuner with M.P.X. Jack $50.00 MUSIC ASSOCIATED 65 Glenwood Rd., Upper Montclair, N.1. 07043 phone 201 -744-3387 i 92 NOTEWORTHY CIRCUIT SAFETY SWITCH FOR MINI -BIKES One index of the ever-increasing popularity of the minibike with the -is younger set-particularly those too young to own or operate cars the number of injuries noted by hospitals and pediatricians. Many of these injuries occur when the rider's clothes switch made by sealing two contacts in each end of a 5 -inch length of glass or plastic tubing bent in the form of a "V ". One contact on each end is grounded to the frame and the other goes to the high side of the coil or to the "hot" lead to the spark plug. The switch is clamped to a piece of 1/4" plywood and mounted vertically MOUNTING BOARD TO COIL PIPE STRAP OR SIMILAR TO FIT TUBE HEAVILY INSULATED COPPER WIRE (I STRAND) - GROUND LUG (IN SOME CASES WHERE COIL IS NOT GROUNDED GOES TO SECOND COIL LEAD ) BARED TINNED WIRE CONTACTS GROUNDED SCREW EPDXY RESIN, PLASTI -BOND. ETC. GAP BETWEEN CONTACTS LARGE ENOUGH TO PREVENT ARCING GLASS OR PLASTIC TUBE \ ' MERCURY -ANGLE TO SUIT WRAP STRAPS WITH CELLULOSE SPONGE OR TAPE /APPLICATION SEE TEXT or some part of his person gets caught in the rear -wheel spokes or between the chain and sprocket after a spill. Being aware that the rider does not have time to cut the ignition when he realizes he is about to spill; Mr. Lindsey Ford, Balwyn, Australia developed a simple switch that kills the engine when the bike tips. The diagram shows how he described the switch in Electronics Aus- tralia. It is actually a simple mercury across the frame parallel to the han- dlebars. It should be wrapped in foam rubber to protect against shock and enclosed in a small box to protect against the elements and gas and oil spillage from the engine. The angle of the "V" is determined by the type of vehicle. If the angle is too large, the ignition will short out on a normal leaning turn. If it is too small, the igni- tion might not cut off if the rider takes a spill on a hill. R -E _iár r cerslEK Z1YGEaTIFICATa ... (,kkATEUI( FT-243 ZIP caTSTAL PUUR,CaRA^SE'"c' E,,R.T..If.I.C.A->7E-- N cj VV... YOU C A N VP-ORDER Amateur, Monitor and CB CR Y S TA LS Your dealer has a new, fast, direct factory ZIP Crystal Purchase Certificate hat enables you to get the Amateur controlled Quality Crystals you want nailed direct to you promptly. Ask about it. CRYSTEK formerly Texas Crystals DIVISION OF WHITEHALL ELECTRONICS CORPORATION 1000 Crystal Drive Fort Myers, Florida 33901 4117 W. Jefferson Blvd. Los Angeles, California 90016 Circle 83 on reader service card RADIO- ELECTRONICS www.americanradiohistory.com COMPLETE TUNER SERVICE Castle, the pioneer of television tuner overhauling, now offers the following services to solve ALL your television tuner problems. - OVERHAUL SERVICE All makes and models. VHF or UHF tuner (1960 or lofer) TRANSISTOR tuner $9.95 $9.95 UNIVERSAL REPLACEMENTS Prefer to do it yourself? STOCK No. HEATERS SHAFT Min.* Max.* I.F. OUTPUT Snd. Pic. PRICE ... COLOR tuner (Guaranteed color alignment no additional charge) $9.95 CR6P Parallel 6.3v 13/4rr 3" 41.25 45.75 8.95 CRIS Series 600mA 13/4rr 3" 41.25 45.75 9.50 Overhaul includes parts, except tubes and transistors. CR9S Series 450mA 13/4rr 3" 41.25 45.75 9.50 Simply send us the defective tuner complete; include tubes, shield cover and any damaged parts with model number CR6XL Parallel 6.3v 21/2rr 12" 41.25 45.75 10.45 and complaint. Your tuner will be expertly overhauled and CR7XL Series 600mA 21/2rr 12" 41.25 45.75 11.00 returned promptly, performance restored, aligned to original standards and warranted for 90 days. CR9XL Series 450mA 21hrr 12" 41.25 45.75 11.00 ... Dismantle tandem UHF and VHF tuners and send in defec- 'Supplied with max. length selector shaft (measured from tuner front tive unit only. apron to tip) you cut to suit. Remove all accessories ...or dismantling charge may apply. ® EXCHANGE REPLACEMENTS TtcuohnemisnpegletCeaansdwtleithUrHehFpalarpdcowesmaitrieeonntantwduinthecrospmluapgroeneinanpltlutkeitqfoutorippUaedHdaFpwttuiftnoherr.mveTsmheeroynry fine come thou- sands of popular TV receivers. qe When our inspection reveals that original tuner is unfit for overhaul, we offer an exact replacement ( new or re- EXACT REPLACEMENTS built) as low as $12.95 exchange, depending on type. If exact replacement is not available in our stock we custom rebuild the original at the exchange price. Purchase outright ... no exchange needed. $1 5.95 ea. Castle replacements made to fit exactly in place of original tuner. Available in the following popular numbers. PROFESSIONAL "CONTACT OVERHAUL" KIT Do your own minor tuner over- hauling by using this professional kit of chemicals. Enables you to recondition the switching contacts with the same advanced cleaning, polishing and lubricating mate- rials used by Castle. Attain the same professional results we ... do in most cases you can do this right in the customer's home. Safe for all types of tuners, one kit will process several. Order Now ... or write for more inform atü on. Dealer Net $5.50 ZENITH RCA 175 -168 175 -204A 175.264 175.268 175 -740 175 -750 175 -752 175 -754 175 -711 175 -716 175 -755 175 -756 175 -718 175 -719 175 -758 175 -759 175 -721 175 -722 175 -738 1 75.761 175 -762 175 -763 175.739 175.764 'Supplied with new dial is not used. 175 -1104 175.1105 175 -1156 175 -1157 KRK 103A KRK 103C KRK 123D KRK 127AB 175-1106 175 -1160 KRK 103F KRK 127BA 175 -1118 175 -1121 175 -1161 175 -1162 KRK 107A" KRK 1078' 175 -1122 175 -1163 KRK 107C" 175 -1131 175 -1164 KRK 107D' 175 -1132 175 -1165 KRK 107E" 175 -1134 175 -1168 KRK 108A" 175 -1151 KRK 108B" 175 -1154 KRK 1080" 175 -1155 KRK 108E' channel indicator skirt knob, original illuminafed Order EXACT of Main Plant REPLACEMENTS, (Chicago) only. UNIVERSAL Overhaul REPLACEMENTS and "CONTACT OVERHAUL" KITS out Service, Exchange Replacements and Custom Rebuilding available from New York or Chicago. CASTLE TV TUNER SERVICE, INC. MAIN PLANT: 5715 N. Western Ave., Chicago, Illinois 60645 EAST: 130 -01 89th Rd., Jamaica, N.Y. 11418 Circle 84 on reader service card cash in on a GROWING NEW business... INTERNATIONAL CRYSTAL MFG. CO., INC. 10 NO. LEE OKLA. CITY, OKLA. 73102 SERVICE ..- MICROWAVE OVENSThousands of new microwave 'ovens are sold each year for ... commercial opportunity opens for those presently opportunity to supplement your present or home engaged income use. As oven in radio and or start an sales continue to climb a brand television servicing. It's an entirely new servicing business. new ... AHpenorlueewmnccdtoarfrooojeorkndreiiscttdyhioosofvfrfeonrnzteehewsewntahffsuirocearoharndvncictchsuiininstsgeamdrceianonu"odfdtakeisissnmct.goafvHoitneioomtrdmeine'negaoefrnwaotchtmneienegrhbsoouveuseesirnvtnsaeebtrsthylosiaws.thmhmewinreieulnltteasbsraeakreebeuacesoivpnmeognitnamgtsoeiccarioownnwadfraisevv.eeoPfmorvetinhepuenatsree.s, heat yourself International Crystal regarding this space Mfg. Co., a pioneer manufacturer of microwave ovens, -age opportunity for skilled technicians. Write today for has information complete details. ADDRESS INQUIRIES TO: SERVICING INTERNATIONAL CRYSTAL MFG. CO., INC. 10 North Lee Oklahoma City, Okla. 73102 Circle 85 on reader service cardPdfCompressor 6.0.543 CVISION Technologies