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Document DEVICE REPORTRadio-Electronics-1970-10
cuy 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

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JI1 from Technician to by studying at home with

Orantljam Stilool of engineering
bas contareS on
ofjn Qoe

gsoociate in Science in Cilrctronico Qnginuring

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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.

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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

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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

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MODEL
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Automatic triggering mode

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One Year Warranty
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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
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1 pair of crystals, 1 set of standard batteries and Tone.

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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.

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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
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Want to
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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.

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Tell Your customer how Opti -Vue guarantees the finest color he's
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Now, you've secu-ed the part of
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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

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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.

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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

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Circle 12 on reader service card

17

www.americanradiohistory.com

NTS outs a whole new world at your tinúu'tivs.

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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
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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.
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We aacN your electronics course with kits to make
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Field- Effect Transistor Volt -Ohm-
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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
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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.
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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

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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

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Transistor-TV Servicing Made Easy

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How to Hear, Police, Fire,

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LEN BUCKWALTER. After World War police, fire, and aircraft radio moved

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HI -FI STEREO

101 Questions and Answers

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bpmtcroylieicvetaFehsOlroRtdethEhqeSteuoTiipneHbmlg.eoeeBctnnhtEritLo.omTnu.IisetcTch"thah1aines-ndn2ibc-o3apmol-rk4eoa"ccnfheidrreasedntepsilcaaetpacior-l-

tpmFhrieuninlatmclilpiyepl,telhextohsdaeontbfdooaaotuaukpttooesmhscotoawebrrsteirlohiedosgwysestettseorymesoastep,. mpflmsy.

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Aviation Electronics, 2nd Edition

nsaamtmstbbreiyvuioyagmceusitonniaatonKaskess,tminEmpiucuosIfooraaT,ssonipntten,HriiadedgceoanreWalnnaeiedridns.tcqdrsiictBureoarraaeOrnionvapenncgSni,flmtddEatiaiinc.taoteiowseeinnoTnnweddene-thrs,fnaqstiidtermotsunheoeurmidsepvxpdam,erirpmniacranleyipseracertna.,isaeitnlnditnontcds-aa.tgaailsnrseanltC,,dht,ncahoetAcdeneavsoicTcnydemnheosderCg-s---f--

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Questions & Answers

on Short -Wave Listening

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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-.

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RE -100

Send books checked at right

enclosed

Send FREE 1970 Sams Book Catalog

20785 20764 20780

20777 20767 20781

Name
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Address

L City

State

lip

Circle 18 on reader service card

20776 20743 20783

20782 20737 20779
J
27

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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
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IF YOU'RE OUT TO BAG A BETTER JOB in Electronics,
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Right now there are 80,000 new openings every
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But you do need knowledge, knowledge of electronics fundamentals. And there is only one nationally accepted method of measuring this knowl-
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Why a license is important

An FCC License is a legal requirement if you want

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two-way mobile radios, microwave relay links, radar,

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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

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Ed Dulaney, Scottsbluff, Nebraska, for example, passed his 1st Class FCC License exam soon after
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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."

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Please send me without cost or obligation: tttohrodeYnmaiyoc.u,sr"an4d4de-sphcaorgiwbeinybgoouolrokbc"ooHuporpswoerstutocnaitnSieuspcrcieenpeadErleeIcnmtroeEnlifecocs-r
Your book on "How To Get A Commercial FCC License."
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OCTOBER 1970

Circle 19 on reader service card

Age__
RE -83
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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
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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

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New 4-cimiinci

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by WALTER G. SALM

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3 -
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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

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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

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ORCHESTRH

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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

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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

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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

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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

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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

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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

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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)

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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!

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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.
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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.
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57

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( 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

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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

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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

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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
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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.
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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

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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
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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. Richman
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A286/507 SOLID-STATE ELECTRONICS by R. G. Hibberd Pub. price, $9.50 Club price, $7.95
389/608 PRINCIPLES OF DATA COMMUNICATION by Lucky, Weldon & Salz Pub. price, $14.50 Club price, $11.60
A347/506 ELECTRONIC DIGITAL TECHNIQUES
by P. M. Kintner
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A037/604 DIGITAL LOGIC AND COMPUTER OPERATIONS by Baron &
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350/434 DIGITAL COMPUTER USER'S HANDBOOK by M. Klerer & C. A. Korn Pub. price, $27.50 Club price, $23.35
A565/031 AMPLIFIER HANDBOOK by R. F. Shea
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Special $1.00 bonus book comes to you with your first club selection

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TRANSISTOR CIRCUIT DESIGN by Texas
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PRINTED CIRCUITS HANDBOOK by C. F. Coombs, Jr.

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MODERN COMMUNICATION PRINCIPLES by Stein &
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Save time and money by joining the

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Electronics and Control Engineers' Book Club

ELECTRONICS AND CONTROL ENGINEERS' BOOK CLUB 582 Princeton Road, Hightstown, N.J. 08520

HERE is a professional club designed specifically to meet your day -to-day engineering needs by providing practical books
in your field on a regular basis at below publisher prices.

How the Club operates: Basic to the Club's service is its publi-

cation, the Electronics and Control Engineers' Book Club Bulletin, which brings you news of books in your field. 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

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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

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$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
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POSITIVE CONTACT p.EANER AND LUBRICANT
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Circle 63 on reader service card

RADIO -ELECTRONICS

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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'

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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

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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-

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and finished in a flaw-

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finished in classic Salem

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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. ..
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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-

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age shelf. Assembled

GRA-203.20 Cabinet, 45

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$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

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Address

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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

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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

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LAFAYETTE Radio ELECTRONICS Dept. 17100

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I Send Me the Free Lafayette Golden Jubilee 1971 Catalog 710

mi

1 Name

17100

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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

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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-

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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,

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WANTED

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COMPONENTS, unused BARRY, 512 Broadway, 212 WALKER 5-7000

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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 card


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