3. › archive-radio...vertical problems, by paul goldberg (a work bench feature) 24 techniques...

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RADIO -TELEVISION SERVICE DEALER MARCH, 1955

ypes eft de SI}430., 5114G6, 6AX4GT, 65F17BTA, 65472TB, tY J6, 25CU6.

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THAT GIVE YOU MANY ADVANTAGES AT NO EXTRA COST

For example Raytheon 6SN7GTIl has these advantages:

Bumper point micas top and bottom - mount is held rigid in bulb to reduce vi- bration and microphonics.

O Slot in micas to reduce leakage between sections.

O Cathode pinched above top mica for tighter mica cathode fit - lower micro - phonic level.

O Short strong leads support mount at several points.

© All plate tabs pinched or welded above top mica and below bottom mica to strengthen mount.

O Improved grid design for sharper cut off.

O High conductivity grid winding wire to eliminate grid emission.

O Short leads - direct to pins.

Strict control of plate diameters (Geom- etry) for uniform characteristics.

G Shorter over all length to improve rigidity.

The lessons learned in structural strength of tubes while developing "rugged" types; the vast warehouse of knowledge about how to make tubes reliable gathered while developing and producing RELIABLE tubes; the revolutionary new thinking and pioneering resulting from the development of the rigid, straight lead Raytheon BANTAL Tubes; the boundless skill, know-how and craftsmanship gathered while designing and producing more than 250 million receiving tubes, millions of special purpose and picture tubes, and millions of semiconductor products; all this experience, gathered through more than 30 years, makes the new Raytheon 6SN7GTB and other tubes in this series - the finest Raytheon Receiving Tubes that we've ever produced.

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RADIO -TELEVISION SERVICE DEALER MARCH, 1955

EDITORIAL STAFF

Publisher

SANFORD R. COWAN

Editor SAMUEL L. MARSHALL

Editoricl Production ROBERT CAMPBELL

Contributing Editors ROBERT 7. DARGAN

PAUL GOLDBERG OSCAR FISCH

SAN D'ARCY

BUSINESS STAFF

Advertising Manager HARRY N. REIZES

Advertising Sales

LAWRENCE STEINER

Production Manager DAVID SALTMAN

Circulation Manager HAROLD WEISNER

Ass't Circ. Mgr. C. J. BINDERMAN

BRANCH OFFICES

LOS ANGELES TED E. SCHELL

2700 West Third Street Dunkirk 2-4889

CLEVELAND RICHARD E. CLEARY 15515 Detroit Avenue Cleveland, Ohio LAkewood 1-7125

MID -WEST ED DAMER

333 N. Michigan Avenue Chicago 1, Illinois FRanklin 2-7100

EVERY SERVICE FIRM OWNER IN THE U.S.A.

Receives SERVICE DEALER Monthly Distribution of this Issue over 70,000

Member 0 PA -Circulation Statement sent on request

VOL. 16, NO. 3 MARCH, 1955

FEATURE ARTICLES

Roundup of Indoor P.A. Components, by Sol Heller 11 A comprehensive appraisal of late developments in the P.A. field, and general applications of individual units

Chrominance Systems in Color TV Systems, Part 4 by Bob Dorgan and Sam Marshall

Block and circuit diagram analysis of basic color demodulators

TV Instrument Clinic, Part 9, by Robert G. Middleton 23 Servicing techniques involving identification of scone patterns

Vertical Problems, by Paul Goldberg (a Work Bench Feature) 24 Techniques involved in dealing with vertical circuit defects

TV Service Information Sheets 25-32 Complete preliminary service data for Capehart CX-38

Servicing With the Square Wave Generator, by Oscar Fisch 34 Interpretations f square e test co-ra._ ei and a resume of the many applications of this instrument

A Miniature Volt -Ohmmeter, by Edward McArdle 41 _xtreme utility in a Volt -Ohmmeter that may be carried in your shirt pocket

15

CIRCUIT AND SERVICE FORUM The Work Bench

Admiral 19FIA: Fold -over at bottom 24 Emerson 734B, Ch. 120169-B: Vertical Frequency drift 52

Answer Man Admiral 21 FI: No Vertical Deflection 36 picture Tubes: Arcing in Neck . 36

Video Speed Servicing Systeme Fada Mod. S 1055 37

Rider TV Field Manual Service Data Sheets Zenith Mod. K2872R, K2873E, Ch. 28K20 39

DEPARTMENTS

Editorial 4 Work Bench 24 Trade Flashes 6 Answer Man 36 Association News 16 New Products 46

Advertising Index 56

RADIO -TELEVISION SERVICE DEALER is published monthly by Cowan Pub. Corp., 67 West 44th St., New York 36, N. Y. Subscription price: $1 for 2 years in the United States, & U.S. Poss. Elsewhere $1 per year additional. Single Copies 25c. Reentered as second class matter Sept. 25, 1950 at the Post Office at New York, N. Y. under the Act of Mar. 3, 1879. Copyright 1955, Cowan Publishing Corp.

POSTMASTER: SEND FORM 3579 TO RADIO -TELEVISION SERVICE DEALER, 67 WEST 44th ST., NEW YORK 36, N. Y.

RADIO -TELEVISION SERVICE DEALER MARCH, 1955 3

EDITUßIL... Wholesale Servicing Opposed

Our Nov. 1954 editorial disclosed that additional income is being obtained by many large service firms who now specialize in or make a practice of doing service work for less competent technicians or for smaller service firms which are either under- manned or overloaded with repair jobs.

This published observation brought an avalanche of critical letters from subscribers who are adverse to the practice of wholesale servicing. Having eval- uated the many opinions expressed we are now inclined to believe that our critics have made out a very good case against the practice.

Practically every one who wrote stressed that in his own particular community there are many legitimate, ethical and responsible service firms who are successful despite the great competition- and that in addition there are a very large number of part-time servicemen who as a general rule provide irresponsible and unethical price -cutting competition. This group of part-timers, it seems, in the majority of cases, either because of incom- petence or lack of proper test equipment, have "loused up" jobs so badly and so often that they must call upon real professionals to get "bailed out" of their self-imposed jams. That is-some of the more responsible part-timers seek professional aid whereas the irresponsible part-timers generally do NOT-and from this stems the greatest danger- the public's condemnation of the service profession as a whole.

An established service firm quite naturally tries fáithfully to satisfy its customers in every respect. In contrast, the part-time servicer, having much less at stake, does not as a rule, maintain such high ethical standards. By working at cut prices part- timers in general seem to have the idea that his occasional customer is only getting the degree of service he is paying for-a low fee, an inferior type of service.

That being so, it is the consensus of professional service firm owners that under no circumstance should they aid and abet their most unethical, price -cutting competitors nor should they collab- orate with the part-timers who, as a general thing, have been most guilty of undermining the set - owning public's respect for servicemen as a group. There's too much logic to that line of reasoning to refute, hence this addenda to our November editorial.

by S. R. COWAN PUBLISHER

PREDICTIONS AND RESULTS

Unfortunately, my editorial remarks and predictions of an opposing -popular -view -nature are borne out and become reality all too often. When that happens, I could gloat, but there's nothing to be gained from being an "I told you so" guy.

Time and again, since December 17, 1953, when FCC gave compatible color TV the "green light" I alone of the technical trade journal editorial writers warned servicemen not to expect, as was blatantly predicted by others, that color TV would achieve mass production in short order. In Feb- ruary 1954, when others were still saying that color TV production would run from 100,000 to a million units in 1954 I warned that because of technical difficulties and cost factors it was quite likely that actual color TV production would probably not exceed 30,000 to 50,000 receivers. 1954 production figures will soon be available and they'll show I was quite right.

Several years ago I complained that too many so- called FM stations were following the wrong practice in playing so many ordinary commercial phono records having a 60-5000 CPS range. Now the record shows that most of the stations guilty of that "do it the easy way" practice have failed and have gone off the air. Sorrier still, most of the dealers in those stations' range, having sold customers FM receivers, are wrongly blamed by the set -buying public for having tricked them into a bad deal. But then, those of us in the servicing field are always being blamed for the other guy's fault.

Early last year I opined that too many new uhf TV stations not having TV network affiliation were going on the air, and thus were going to give their audience inferior programming, which in turn would endanger the stations' success and cause much grief amongst the TV viewers in those areas. Alas, the record again shows that many uhf stations have gone on the air and off again merely because they did not have network affiliation and thus their programming was so bad as to not justify public support. However, this sad practice may be brought to a halt. Last March 26th there was released an announcement that FCC had authorized AT&T to build 14 microwave relay stations to carry network programs to TV stations in New Mexico, Minnesota, and Wisconsin. We all hope for that day when networks will extend from coast to coast and village to village. Then uhf can be said to have grown into long pants.

4 RADIO -TELEVISION SERVICE DEALER MARCH, 1955

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Trade Flashes

Legislation to curb fraudulent prac- tices in the testing and repair of television receivers and gas and electric appliances was introduced recently in the New York State Assembly. The bill covers unnecessary parts installation of any nature, and unnecessary service work in general, and requires that the serviceman submit a highly comprehensive itemized bill describing in detail the nature of replacement parts by number or symbol, and an itemized bill for his labor.

Color TV status throughout the nation: A representative of Raytheon declares that they will produce up to ten per cent of the total national output of color TV sets for 1955. Development of a color set in the 500 -dollar range is not expected until 1957 ... CBS-Hy- tron will market a rectangular color picture tube within the foreseeable future ... Estimates of 1955 color set production . . . Total national production of color TV sets for 1955 will reach 300,- 000, according to Raytheon, though DuMont pegs it at 150- to 200,000. ... NBC plans to maintain and develop its color programming schedule.

The National Fire Protection Associa- tion recently risked RETMA to mod- ernize the National Electric Code in accordance with new electrical developments. RETMA, in turn, selected Doug Carpenter for the job. Doug is Chief Antenna Engineer for the JFD Manu- facturing Co. Inc. The Association aims to improve methods of fire protection and prevention. Its membership is composed of over 15,000 individuals, cor- porations, organizations, etc., the majority of which are insurance companies and government agencies. Their Na- tional Electric Code is the accepted guide for all licensed electrical installations.

Retail sales of television receivers in 1954 increased by nearly 1 million units from the level of 1953 to establish a new high, and, in addition, manufacturers of cathode ray tubes sold nearly 10 million units during 1954 to establish a new record. For both cathode ray and re-

/

ceiving tubes, sales in December were above the level of the same 1953 month, the Association said.

EICO, of Brooklyn, N. Y., has just re-

leased their new 1955 Tube Tester Roll -

Chart No. 625-04. This roll -chart con-

tains hundreds of listings of the latest tubes just newly released by all the

leading tube manufacturers. It thus

widely increases the utility of all EICO

Tube Testers.

Dr. A. Melvin Skellett, research engineer who holds more than 70 major patents in electronics, has been named director of color television tube planning and development for Tung -Sol Electric Inc..

For the past 25 years he has been ac-

tive in the electronics industry in re-

search and administrative capacities, including 15 years on the technical staff of Bell Telephone Laboratories.

Patent No. 2699500 has been issued

to Telrex, Inc., Asbury Park, N. J., cov-

ering its well-known "Clover V -Beam" TV Antenna, which feature closed loop conical -v -beam dipoles and a unique transposed phasing harness which makes it possible to provide a wide aperture, high gain, 2 -bay TV array which is small and light in weight.

On April 19th, General Electric will initiate its nationwide TV -Serviceman public relations promotion program. En- titled "TV Service Month," and imple- mented by mammoth ads in Look magazine, the program will feature a large cash prize contest for service customers. Entry blanks will be made available to the public through GE retailers, who will be stocked with promotion items by their GE distributors, and whose names will be listed, upon request, in exten- sive Look magazine ads. For program details, write GE, Tube Dept., Schenec- tady 5, New York.

The Cooper Union Alumni Associa- tion has designated William Dubilier, founder of the Cornell-Dubilier Electric Corporation, to receive the first annual

[Continued on page 42]


DELCO RADIO'S Model 8007 A Terrific Value at Moderate Cost

DELCO RADIO

A GENERAL MOTORS PRODUCT A UNITED MOTORS LINE

DISTRIBUTED BY ELeCTRONICS WHOLESALERS EVERYWHERE

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MODEL 8007-The Speaker with Thousands of Replacement Applications!

Here is a sensational performer in the big Delco Radio line of speakers ... a Hi-Fi replacement speaker for AM, FM, and TV receivers and phonographs that matches their service requirements with a voice coil impedance of 4.1 ohms-not too high, not too low, but just right! And it's ideal, too, for custom- built high-fidelity systems. Wherever installed, the model 8007 Delco Hi-Fi speaker will give new sparkle and life over the full tonal range.

Here are some of the reasons why: Its 8 -inch curvilinear cone extends the Highs, gives maximum perform-

ance over a range of 50 to 12,500 cycles per second A heavy Alnico -5 magnet provides peak damping action, high output with clean performance, light highs, heavy lows Power rating of 10 watts Input impedance of 4.1 ohms. A 1%6 -inch voice coil for excellent damping effect, high efficiency, minimum distortion Total these features, add a rugged, zinc - plated, attractively painted basket, and you have the outstanding speaker in its price range ... the Delco model 8007!

The Most Highs ... the Most Lows ... the Most Watts ... in a Medium -Priced Speaker

DELCO RADIO DIVISION OF GENERAL MOTORS, KOKOMO, INDIANA


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PHILCO TUBES IMPROVE THE

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These top features assure Philco StarBright dealers of top sales .. top profits in picture tube replacements. They mean sharpness, clarity,

detail and over-all performance that give "You are There" realism.

Right in your neighborhood there are hundreds of TV set owners

who want the new, fresh, vital picture that only a Philco StarBright

20/20 can provide. Now is the time to sell them .. and the Philco

StarBright 20/20 can be installed in practically any make TV.

Your customers want a quality picture-they know Philco- famous for quality the world over. Put the two together and you've

started sales and profits rolling your way. Call your Philco Distributor

today for complete details on this money making program.

th. eit legre 4E1 KA1

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NEW 1955 PHILCO

SHAREawdPROFIT OPPORTUNITY!

Service Dealers everywhere are going to make more money with

Philco this year. Bonus dollars and profits are yours with no

additional effort through one of Philco's greatest promotions.

Call your Philco Distributor at once for complete details.

PHILCO CORPORATION ACCESSORY DIVISION

"A" AND ALLEGHENY AVE., PHILA. 34, PA.

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roundup of indoor

O.A. Components

SOL HELLER

ALTHOUGH we are well advanced in the season of the year and in-

door public address work is just about stabilized, interest in its technical phases increases. The round -up of data presented in this article should therefore prove timely, and of value to both beginning and advanced pa technicians. The author makes no pretense of its being complete or comprehensive, although much effort to achieve maximum coverage has been made. The identities of companies who have supplied the data on which this article is based are obvious either from the text or illustrations.

Amplifiers One of the more important com-

ponents of the indoor pa system from a point of view of servicing, is the am -

Fig. I-Altec-Lansing Limiter Ampli- fier Model A -322C. Note rack mount-

ing features.

plifier. The amplifier provides control over other units in the system; it is also capable of compensating for defects or undesirable characteristics in these units. Another reason for the importance of the amplifier rests in the fact that it is

more susceptible to failure, and may thus require more service than other component. Care then should be used in choosing the proper amplifier for the system you plan to set up.

Tone controls are important parts of an amplifier. Differences in acoustic conditions, volume levels, microphones, pickups, speakers and records necessi- tate varying degrees of boost or attenuation of bass, treble and high frequencies. At low volume operation, bass com- pensation is needed. This is so because the ear's response to low frequencies falls off markedly when volume is decreased. High -frequency attenuation may be necessary to minimize distortions in phonograph records, and needle scratch. Bass attenuation is called for when low -frequency noises are interfer- ing with the clarity of speech, or when "boominess" is introduced by room acoustics. Check the tone control set-up on the amplifiers you are considering for a particular installation, and note any advantages one may offer over another in this respect.

A number of interesting features are present in amplifiers that are currently being manufactured. Altec-Lansing, for instance, is putting out a Limiter Am- plifier (Model A -322C) Fig. 1 which compensates for the undesired variations in volume that tend to occur when the

person using the mike changes his position with respect to it. It also permits operation of the pa system at a

higher level of sensitivity without danger of feedback. When used in conjunction with a high-powered pa system, the Limiter Amplifier prevents volume peaks from causing loudspeaker failure.

In the series of Bogen J series amplifiers provision is made for rapid conversion to low impedance microphone in- puts through the use of plug-in transformers. The amplifiers are normally supplied for high impedance microphones but through the use of an inexpensive plug-in transformer they are readily converted to low impedance microphones.

The Bogen JX30 and JX50 amplifiers have provision for reducing or eliminating annoying feedback when the amplifiers are used in indoor installations. See Fig. 2.

There is also the Bogen JOH pre- amplifier which can be used with the type F1050 and F10125 booster ampli -

Fig. 2 - Bogen J Series Amplifier. Plug-in transformers are used.

RADIO -TELEVISION SERVICE DEALER MARCH. 1955

fiers. There is practically no limit to the number of booster amplifiers that can be paralleled and there is one installation where H0125 amplifiers are paralleled to provide a total power output of 4,000 watts.

The Stromberg -Carlson AP -54 power amplifier is a 250 -watt unit that may be used in large -sized indoor areas, partic- ularly where the ambient noise level is high, incorporates two protective relays. One is a thermal relay (K-1, Fig. 3); the second is a magnetic relay (K-2). The two in conjunction prevent the application of ac voltages to the plates of the 866A mercury-vapor rectifiers for about 45 seconds after the amplifier has been turned on. This permits the 866A cathodes to reach operating temperature before they begin emitting. (In mercury- vapor rectifiers, damaging arc-overs tend to occur between plate and cathode if the cathode temperature is below normal when plate voltage is applied.)

A current -measuring meter is provided in the amplifier, to permit rapid tests of the various tubes and circuits in the amplifier. A meter switch permits measurements to be made in each stage. When meter readings occur outside a calibrated area on the meter, a defect in the stage being checked is indicated.

In Newcomb Custom K Series amplifiers (Fig. 4), audio bandwidth selectors are present that permit the selection of various upper -limit frequencies. These selectors, which are not tone controls in the usual sense, permit the elimination of annoying vocal or instrumental distortions. The attenuation of the of- fending high frequencies does not affect the remaining high, middle and low frequencies.

A dual electronic eye is incorporated in these amplifiers; this device indicates even slight overloading of the output tubes, and thus calls attention to in- cipient distortions before they become audible. A calibrated control is present that permits measurement of output volume in watts. Separate treble and bass controls permit regulation of tone without any reduction in volume. An. other feature is a remote control unit that enables the pa system operator to mix and fade individual mikes located up to 2,000 feet away.

AMPLIFIER AND SPEAKER REQUIREMENTS

MOTION PICTURE THEATER CONDITIONS

Persons And/Or Seats Amplifier

No. Of Speakers

750 20 Watts 1

1500 30 Watts 2

3000 60 Watts 3

6000 80 Watts 4

Fig. 5 - Amplifier and speaker requirements. (Electrovoice)

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Amplifier and Speaker Require- ments in Different Installations

1 h determination of how much amplifier power is necessary for a given installation, as well as the number and power rating of the speakers needed, has some tricky aspects. One component

Fig. 4-Newcomb Custom K Series Amplifier with bandwidth controls.

manufacturer has devised an intricate chart to help the technician in this respect; another manufacturer questions the accuracy of such charts, and musters strong arguments in support of his position. A rather simple method to use when in doubt is to check an installation similar to the one you intend to set up, and find out what the amplifier power and speaker set-up is there.

It should be pointed out that a speaker's wattage rating is not necessarily an index of its efficiency. Speakers with lower wattage ratings may be more efficient than higher -wattage units; a speaker's characteristics must be considered as a whole, and compared to the requirements of the particular installation, to determine its suitability for that installation.

Keeping this caution in mind, it is interesting to examine a table provided by one speaker manufacturer (Electro - Voice) with regard to amplifier and speaker requirements (see Fig. 5). In

AP -54 Power Amplifier.

the "no. of speakers" row, the manufacturer of course has his own speáker in mind; the unit is a coaxial type called the Compound Diffraction Pro- jector, uses two horns of different sizes and has a rated input power of 25 watts. A speaker of comparable efficiency made by any other manufacturer can be substituted in this column.

The table covers conditions in motion picture theaters. If a pa installation is to be made in an auditorium, double the amplifier power and the number of speaker units. For factories and other sites where the ambient (i.e., surround- ing) noise is even higher, multiply the basic requirements of a quiet motion picture theater by three-that is, use three times the amplifier power, as well as three times the number of speaker units employed in the case of the quiet theater. Fig. 6 illustrates two relatively high and low wattage speakers.

Choosing Loudspeakers Some of the considerations that must

be taken into account in choosing the speakers to be used in a pa installation are as follows:

1. Is the pa system to be a high -power or low-level set-up? If it's to be a low- level one, paging and intercom -type speakers-i.e., small, medium -efficiency units-will serve very well. If high power is needed, large trumpets and radial projectors with heavy-duty driver units are generally necessary.

2. Is music to be reproduced? If it is, the speaker (and amplifier system) will, desirably, have a relatively low cutoff frequency, as well as an ex- tended frequency range. In locations where reverberation is a problem, however, speakers with a higher low -frequency cutoff may have to be employed; low -frequency reverberation will be re- duced at the expense of fidelity, in such a case.

3. Does sound have to penetrate a


Fig. 6A-Speaker by University.

Fig. 68-Speaker by Quam-Nichols.

Fig. 6C-Soeaker bg Jensen.

Fig. 6D-Speaker by Permoflux.

great distance from the speaker? If it does, a large trumpet with a sharp sound distribution pattern is called for.

4. Is the noise level at the site of [Continued on page 52]

For instruments actually ahead of today's circuitry ...ready for the day when color TV becomes as general as today's

black -and -white sets...look at the Hycon line, designed with tha electronic serviceman in mind. Accurate enough for critical work ir_ the

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MODEL 617 3- OSCILLOSCOPE Designed both for color TV servicing and

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in

Cote TV kcivete

BOB DARGAN and SAM MARSHALL

Part 4

IN the previous installment it was pointed out that the color demodu-

lator performs the function of convert- ing the color-sideband signals contained n the chrominance (chroma) signal into I/Q or R-Y/B-Y color -difference signals. The block diagram shown in Fig. 1

illustrates the basic process of demodu- lating a chrominance signal. Notice that the filtered output of the in -phase demodulator section contains the I or R -Y color -difference signal, and that the filtered output of the quadrature de-

modulator section contains the Q or B -Y color -difference signal.

Block Diagram Analysis of Basic Color Demodulators

Present color TV receivers employ either high level or low level demodulator circuits. A low level demodulator (Fig. 2A and 2B) is one in which the chrominance signal output requires further amplification before it can be applied to the color picture tube. This amplification is necessary because typ -

CHROMA SIGNAL

90° PHASE SHIFT

QUADRATURE DEMODULATOR

3.58 MC.

OSCILLATOR

IN -PHASE DEMODULATOR

--Envelope

I

q' I

Ova

FILTER

Q OR B -Y SIGNAL

QUADRATURE DEMOD. OUTPUT

FILTER

IN -PHASE DEMOD. OUTPUT

I OR R -Y SIGNAL

Fig. I-Basic block diagram of two-phase demodulation prccess Waveforms shown in figure are not drawn to scale.

ical modulators of the pentode and gated diode types cannot handle large dynamic swings with proper linearity. Signal matrixing in low level systems generally follows the demodulation process. Recovery of the G -Y color - difference signal is then accomplished by mixing correct proportions of R -Y and B -Y in accordance with the formula:

G -Y = -.275 I - .636 Q (or) G -Y = -.51 (R -Y) - .19 (B -Y)

In high level demodulation (Fig. 2C) the output is fed directly to the picture tube. A precision transformer is used to fix the desired ratio of color -difference output voltages and thereby eliminate the need for variable control elements to adjust the ratio. This voltage stepup generally precedes the demodulation process and recovery of the G -Y signal is accomplished by sampling the chrominance signal along the G -Y axis which is 214° removed from the R -Y axis as shown in Fig. 3.

Circuit Diagram Analysis of Basic Color Demodulators

Either pentodes or diodes are used in present-day low level demodulators. The system described in the previous installment is an example of a low level demodulator using pentodes. As shown in Fig. 4, gating is accomplished by the 3.58 me reference signal fed into the suppressor grid. The sharp gating pulses of this signal, developed in the plate circuit, then sample the incoming chroma signal applied to the control



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ASS NEWS

Radio Technicians Association of Southern California

The Radio Technicians Association of Southern California, a non-profit corporation, was started in 1936, in Long Beach, and was granted a charter by the State of California in 1938. Its code of ethics covers the very best business standards. It has grown from the Mother

Chapter in Long Beach to six chapters at the present time, with another chapter in process of organization. Shown above are its newly elected officers, (L to R, rear) Ken Summers, Tech. V.P., Lee Johnson, Pres., Bob Bergman, V.P. (front) P. N. Nibbelin, Sec'v , and Bob Whitmore, Treas.

Radio-TV Technicians Guild of L. I.

(N. Y.)

On Wednesday, January 19, 1955 an article appeared in a Long Island newspaper which spurred the Executive Board into instant action. "D.A. asks laws curbing TV gyps," it ran. The Dis- trict Attorney in his annual report had recommended legislation to permit local control over television servicemen. This factor touched off a series of circumstances which led to an interview with the D.A. by members of the Guild Executive Board.

The Southern Pennsylvania Radio Television Technicians Association (SPRTTA)

This organ üation conducted their annual Election Monday, January 3, 1955. The following officers are to serve for the year of 1955: Willard Strayer, Pres- ident; Joseph Hauser, Vice -President; James Mease, Secretary; Eugene Kline- dinst, Treasury; G. W. Dean, Public Relations Officer, and Clarence Kis- singer, Corresponding Secretary. SPR- TTA on Monday, January 17, 1955



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COLOR [from page 15]

3.58 M . 121 Y

CHROMA SIGNAL

I DEMODULATOR A

R > R FILTER AMP.

I -I AMP. --G Q

DEMODULATOR FILTER -->1 AMP.

3.58 MC. / 90t (A) BASIC I -Q LOW-LEVEL DEMODULATION SYSTEM

(B) > R R -Y I

AMP. Y

BASIC G -Y G Y R -Y/ B -Y MATRIX AMP. >

LOW-LEVEL DEMODULATION A

B -Y > > B Y SYSTEM B -Y AMP. >

CHROMA SIGNAL

TRANSFORMER

R -Y DEMODULATOR

FILTER R -Y

3.58 MC.

RED GRID

12

B -Y DEMODULATOR

FILTER B -Y

BLUE GRID

3.58 MC. 90°

G -Y DEMODULATOR

FILTER G -Y

GREEN GRID

3.58 MC. 214°

(C) BASIC HIGH-LEVEL DEMODULATION SYSTEM

Fig. 2-Comparison between basic low

grid. The filtered output of the demodulator contains the in -phase or quadrature color -difference signal, depending upon which corresponding ref -

Fig. 3 - Relative positions of R -Y, B -Y, and G -Y axes.

and high level demodulation systems.

erence signal is fed into the demodulator. Fig. 4 shows an in -phase section of the demodulator circuit.

Low -Level Diode Demodulation A second type of low level demodu-

lator in which diodes are used is shown in Fig. 5. Here the demodulated output is a function of the diode currents produced by the combined effects of the incoming chroma signal and the local 3.58 me reference signal. Although Fig. 5 shows only the R -Y demodulation section it must be borne in mind that a duplicate section is utilized for the demodulation of the B -Y signal; except that the sampling reference signal is displaced 90° from the R -Y signal.

In the circuit shown, the incoming chrominance signal is applied as two signals, 180° out of phase with each other, to a pair of series connected diodes. The 338 me reference signal for R -Y demodulation is applied to the junction of the plate and cathode connections of VI and V2. The R -Y demodulated signal is then taken off at

the junction of the diode load resistors, R1 and R2.

Analysis of Fig. 5 readily shows that when VI conducts and V2 does not, the side of CI connected to Kl becomes

I , and the R -Y point is positive. This may be seen by tracing the electronic flow from K 1 to Pl through GI to ground, and then up to TI to the other side of Cl. Similarly, when diode V2 conducts and diode V1 does not, the electron flow proceeds from K2 within the second diode to P2, charging C2 negatively on the side connected to P2. On discharge, Cl and C2 discharge in series through R1, R2 and TI. If both charges are equal the potential between the center point of RI -R2 and ground is zero. This center point is where the R -Y signal is taken off. It is obvious that if VI conducts more than V2, the charge on Cl will be greater than the charge on C2, and the R -Y point will be positive. Finally, if V2 conducts more than V1, the charge on C2 will be greater than the charge on Cl and the R -Y point will be negative. These ob- servations are summarized below to assist us in our analysis of the demodulation process.

1. If VI conducts more than V2 the R -Y point will be positive.

2. If V2 conducts more than Vl the R -Y point will be negative.

We will now assume a number of different signal conditions and trace the resulting electron flow and voltage drops produced. To begin with, let us assume a condition where the chroma signal is zero as shown in Fig. 6. In going through a complete cycle, the 3.58 me reference signal makes the plate of VI

G1

CHROMA SIGNAL

0

I OR R -Y SIGNAL

FILTER

OUTPUT SIGNAL I OR R -Y

G3

G2

B+

1IIIIIII.I IIIIIIIII

3.581vG.(D° ()SG.

Fig. 4-Low level demodulator using a pentode. The 3.58 me reference signal applied to G3 samples the in -

phase chroma signal applied to GI, producing an I or an R -Y signal in plate circuit after proper filtering.


CHROMA SIGNAL

TO B -Y DEMODULATOR

CI

Fig. 5-Simplified diagram of R -Y section of bask diode R-Y/B-Y demodulator. In B -Y section 3.58 me reference signal is 90° out of phase with R -Y reference signal.

positive during one half the cycle, and V2 negative during the other half. The direction of electron flow is such as to charge up C1, and C2 as indicated in the previous paragraph.

Since the circuit is symmetrical, the potential on C1 and C2 will be the same. Hence, during the discharge of Cl and C2 in series, through Tl, Rl and R2 in series, the potential at point (2) will be below ground (4) by the same amount that point (1) is above ground. As a consequence point (3) will be at ground potential.

Fig. 6-Equivalent circuit diagram of R -Y demodulator. Heavy lines indicate electron flow for condition of no

chroma signal.

Let us now assume a condition where the applied chroma signal is exactly in phase with the 3.58 me reference signal as shown in Fig. 7A. For purposes of illustration we will further assume that the amplitudes of the chroma and reference signals are equal and have a peak amplitude of E. When the color sync voltage applied to Pl is equal in phase and amplitude to the chroma signal ap- pearing at point (5) no current flows through V1; hence C1 is not charged and remains at zero potential. V2, however, does conduct on the next half of

the cycle, so that C2 is charged to the polarity indicated in Fig. 6 with a potential of 2E since both chroma and reference signals are in series.

During discharge, because there is no potential across Cl, point (1) will be at ground potential, and point (2) will be 2E below ground, making the output signal voltage at point (3) -2E below ground. By a similar analysis it can be shown that a reversal of the chroma signal phase will make point (2) zero and point (1) plus 2E, making the

[Continued on page 471

KEY: i)

VI

V2

VECTOR

DIAGRAMS

AMPLITUDE AND

POLARITY OF R -Y

SIGNAL

3.58 MC. REFERENCE SIGNAL

PI

iK2

Alk .101 L, ''IIII IIIUII,

R -Y AXIS

CHROMA SIGNAL

8-Y

AXIS

(A ) CHROMA SIGNAL IN PHASE WITH

3.58 MC. REFERENCE SIGNAL

2)

el II' , v dlll D

,III

.41\ .i111111).

(Di

45°-a

R -Y AXIS

CHROMA 2, SIGNAL

B -Y AXIS

(B) CHROMA SIGNAL LAGS 3.58 MC.

REFERENCE SIGNAL BY 45°

CHROMA SIGNAL

PI

,Illdlle ,1lollllk

III' tllllIl

I'itik, I I UiL 3IIIII''

R -Y AXIS

CHROMA SIGNAL

B -Y AXIS

ZERO R -Y /SIGNAL

(C) CHROMA SIGNAL LAGS 3.58 MC.


3) SHADED AREAS INDICATE DIODE CONDUCTION

Pt

,,adlllllk ' \ ,IIII IIIIh,;

'llllll'11I''IIID'

0 ; , K2 igr

R -Y AXIS

AXIS

CHROMA SIGNAL

(o) CHROMA SIGNAL LAGS 3.58 MC.


P,

itlll, % '' It,

'1W 'I

K2 O IIIII I I ., ALI

'111IIIIIr

CHROMA SIGNAL

R -Y AXIS

' B -Y

235° AXIS

(E) CHROMA SIGNAL LAGS 3.58 MC.

REFERENCE SIGNAL BY 235º OR LEADS

IT BY 45°

Fig. 7-Conduction of V, and V, takes place when The plates of the tubes are positive with respect to the cathodes. From (A) to (E) are shown conduction periods for various phase conditions between chroma and reference signals.


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I' RADIO -TELEVISION SERVICE DEALER MARCH, 1955

Vert. sync derivative

Camera signal r,

Fig. I - After the composite video signal passes through the clipper circuit, most of the camera signal is

eliminated, leaving the horizontal and vertical sync pulses. This waveform has both 15,750 -cycle and 60 -cycle components; the 60 -cycle sync -pulse residue is seen as a depressed section near the central portion of the dis- play. This depressed portion is sometimes termed sync "punching"; the vertical sync action is not affected

unless "punching" is excessive.

Q. Is it possible for an experienced person to analyze a scope pattern and to tell what is wrong with a circuit in the receiver?

A. To a limited extent, this is possible. To illustrate the extent of the difficulties involved in a complete analysis, however, Figs 1, 2, and 3 show waveforms obtained at different points in the sync system of a receiver. Both vertical - and horizontal -sync -pulse residues are evident in the pattern, and it is apparent in a general way that differentiating and integrating actions are taking place. These waveforms can be compared in shape and in peak -to -peak voltage with the data plovided in the receiver service manual, and a knowledge of whether they depart from normal is thereby easily obtained. However, the next step,

80 -cycle component partially differentiated

Fig. 2 - Here the mixed waveform has passed through a limiting amplifier, which further reduces the camera signal residue; then through a coupling capacitor which imposes some degree of differentiating action on the 60 -cycle component. Sync "punching" is also evident at this point.

TV

INSTRUMENT

CLINIC

PART 9

Based on CHALLENGE CLINIC demonstrations, this

new series discusses many

measurement and test problems raised by service techni-

cians.

By ROBERT G. MIDDLETON

Chief Field Engineer, Simpson Electric Co.

Author of "Pix-O-Fix Troublefinder Guide," published by Rinehart & Co.; "TV Trouble-

shooting & Repair Guidebook," Vols. I & II; and co-author (with Alfred A. Gherardi) of "How to Use Test Probes," published by

John F, Rider, Publisher.

Fig. 3-Now the scope is being applied in the integrator network, and both differentiating and integrating are evident. The partial differentia- tion imposed by the sync amplifier is

still apparent; however, partial integration is also seen, occurring in a direction opposite to the "punching." The integration progresses until the horizontal component is practically eliminated, and only the vertical trigger pulse remains. The kickback from the vertical blocking oscillator is apparent at all points in the integrator circuit as the sharp downward pulse

indicated in the photo.

which concerns identification of faulty components on the basis of the particular distortion which appears, is far more difficult. It may, however, be concluded that the differentiating action is excessive, for example, which would usually indicate a series capacitor having. too low a value, or a shunt resistor having too low a value. But it can be said that this field of troubleshooting is exceedingly complex, and defies a large proportion of the attempts which are made to reduce the data to a utilitarian basis.

It is well to note (Fig. 3) that the voltage of the vertical kickback pulse is

much greater than the voltage of the trigger pulse. This prominence of the kickback pulse is often a source of con- fusion, it being wrongly regarded as the trigger pulse. In casg,of doubt, 'the technician should remove the vertical oscillator tube, to see which component of the waveform disappears.

Q. Why does the shape of the r-f/i-f response sometimes change as the fine- tuning control is turned?

Fig. 4-Varying tuner produces different rf/if response.

A. This change in curve shape, illustrated for a typical situation in Fig. 4, is the result of mixer regeneration. When



TWO vertical problems have been chosen for this installment. With

proper diagnosis problems of this type can be solved with ease.

Admiral 19F1A

The receiver was turned on and the raster showed a fold over at the bottom. The vertical hold was varied and found to be working properly. We concluded, therefore, that the trouble was not in the vertical oscillator section. It is important to mention at this point that there is a fairly good set of rules to follow in cases of this kind which are as follows:

1. When the fold over is at the bottom of the raster the trouble is generally in the cathode circuit of the vertical output tube.

2. Trouble affecting the entire vertical sweep, such as insufficient vertical

The Work Bench

This Month:

by PAUL GOLDBERG

VERTICAL PROBLEMS

sweep with good linearity usually can be most often traced to the plate circuit of the vertical output tube.

Although these are not iron clad rules they do serve as a valuable basis for trouble shooting vertical sweep problems.

At this point, the 6S4, vertical output tube was replaced without effect. A study was made of the grid circuit of the vertical output tube. Fig. 1 A shows the wave form at the grid of the vertical oscillator V303B, 1/2 6U8. It may be observed that when V303 B is cut off, C407 charges through R412, R413 and R414. Now, when the grid leak action of the vertical oscillator permits V303B to conduct, C407 dis- charges through the T40 1 secondary and V303B. This discharge current builds up a magnetic field in T401 which in turn induces a positive volt -

V303 B

1/2 6U8 VERT. OSC. C406 VERT

tt

4.0

1.5 MEG. VERT HOLD.

(A ) PIN No.9 OF V3038 PIN No.6 OF V402

04J_ 77

VERT. OUTPUT

C408 9

0.1

Defective

R414 - 2.5 MEG.

HEIGHT

CORRECT

V402

T402

VERT. co

LIN.

TO VERT. DEFL. COIL

INCORRECT

TO BI -

Fig. I-Partial schematic of Admiral I9FIA.

age at the grid of V303B. This positive voltage on the grid lowers the plate resistance of V303B and allows C407 to discharge more rapidly. When C407 is nearly discharged completely the magnetic field in T401 collapses and drives the oscillator grid negative. The operation then repeats itself.

Knowing these facts the scope was set up and a wave form was taken at the grid of the 6S4, the vertical output tube. The service notes were re- ferred to and it was obvious that the wave form was incorrect (refer to Fig. I B). A voltage leakage check was taken of C408, 1 u f, but it showed no leakage. A voltage leakage check was taken next of C407, .047 u f, but this condenser also showed no leakage. R415, the grid resistor, was then resistance checked and found to measure only


8+

R88 150 K

C66 .0047

V18

6SN7 VERT. OSC.

R89 1 C65 2.2 K 047

1 MEG.

47K

2 MEG.

0.1

I

- - 047

12K

R 90 1 MEG. VERT HOLD

R91 820 K

>81- V19

VERT. OUTPUT

3

2.2 MEG.

--- Pin No.1 of 6W6 ( Unused Pin)

Leaking to Pins No's

2 and 7 2 Meg.

Fig. 2-Partial schematic of Emerson 734B.


O

RADIO -TELEVISION SERVICE DEALER COMPLETE TV SERVICE INFORMATION SHEETS

470/.

470.t

B

A

ft.ßEN.CAeIE INCEDANCE

Figure 1

Zo Ro RI

5 120-n-

72 -n 110

92 I I IOOn

SOUND CARRIER

Capehart CX-38 Series

5o%

30%TILT LIMIT

OSCILLATOR ALIGNMENT CHART

Figure 2

PICTURE CARRIER

(.- NOM/NA L CURVE

Step No.

Set Sweep Generator to:

Set Marker Generator to:

Connect Generator Output Cable to:

Connect Oscilloscipe to:

Set Channel Selector to:

Adjust Refer to Note/s:

1 Sweep 211.25MC, Channel Al 1, 2, 3, 4, 5, 6 Channel 13 215.75MC 13

2 Sweep 205.25MC, Channel Channel 12 209.75MC 12


4 Sweep 193.25MC, Channel Channel 10 197.75MC 10 7

5 Sweep 187.25MC, Channel Channel 9 191.75MC Receiver 9

6 Sweep 181.25MC, Antenna Pin 2 of V204 Channel Channel 8 185.75MC Input (12BY7) 8

7 Sweep 175.25MC, Terminals Channel Channel 7 179.75MC 7

8 Sweep 83.25MC, Channel A2 8 Channel 6 87.75MC 6


10 Sweep 67.25MC, Channel Channel 4 71.75MC 4 9



Scope

Step No.

1.

An exclusive service of Cowan Publishing Corp. br special arrangement with John F. Rider, Publisher

47K

150K

Figure 3

Set Sweep Generator To:

2.

5.

44MC (10MC Sweep)

44MC (10MC Sweep)

44MC (10MC Sweep)

44MC (10MC Sweep)

7.

44MC (10MC Sweep)

44MC (10MC Sweep)

44MC (10MC Sweep)

Step No.

Channel #9 (10MC Sweep)

Set Generator To

4.5MC 50% AM Modulation

25KC Dev. Max. Output 4.5MC

25KC Dev. Max. Output 4.5MC

560 mmfd

1N64

Plate of 1st Video 39.75MC Amplifier

220 Ohm

Screen of 1st Video Amplifier Figure 4

VIDEO I -F ALIGNMENT CHART Set Marker Connect Sweep Connect Generator Generator To: Oscilloscope To: To:

41.25MC

47.25MC

44.1MC

42.5MC

45.75MC

47.25MC

39.75MC

Channel #9 Picture Carrier

Pin #1 of V201 -Grid of First I. F. Amplifier Test Point on R.F. Unit (Pin #4)

VHF Antenna Terminals

Thru a 10K Isolation Resistor To Pin #2 of V204 Grid of Video Amplifier

Thru the Detector Network to First I. F. Amplifier

4.5 MC SOUND ALIGNMENT CHART Connect Scope Connect Vertical Input Gable To

Detector Network As in Figure 5

Direct to Junction C312 & R311

Direct to Junction C312 & R311

Generator To

Pin 2 of V204 (12BY7)

Remove Short From T202 and Connect Set to Antenna. Turn on Station and Attenuate Signal until Noise & Hiss is Apparnet

Set Connected to Antenna with Full Signal 47K

Scope

Figure 5

Adjust

T301 (top & bottom)

L302

L301

R307

L302 560 mmfd

47.25MC

45 75MC

Adjust

T202 (Top)

T201 (Top)

T203 (Bottom)

T202 (Bottom)

T201 (Bottom)

Refer to Note / s

1-2-3-4

1-2-3-5

1-2-3-6

1-2-3-7

T204 (Top)

L201 (Bottom)

T102 (on tuner) T204 (Bottom)

1-2-3-8

9-10

9-10

To Obtain

Minimum

Maximum

Maximum

Min. Noise

and Hiss.

Maximum

Receiver

11-12 13-14

Refer To Notes

1, 2, 3

4, 5

6


IM V401 r r .- oI

SYNC SFR3a 6CS6

Ìé0 litl1.7 OF V01 401

yr

03 00[ NV -

cm

oor Mh0

V402A PHASE SPLITTER

U2 12AU7

N

201.

a0r

m >.OÓ

erl`' 11-4

[Nr

PIN 7 Of VI.30+r

K01

V. 1111 1 OF 1.01

V402B NOR. PHASE DET

V2 )2AU7

iiri0}

01

1201

'le aén

1.04 .T.bIIC

1i[

V501

6AGC. CCLAMP 6BF6

2.17128.

Capehart CX-38 Series

V201 IN LT. 6CB6

aNr

1110. 3300

i 1N.

PO

nn

aN.T .aw NY

r Sow ,tAév,

RT.

130

.08

.2

RIO 100

3 fer. oor

I

4

V202 cN. 2N I.F.

6CB6

6' te

1000

z

!If "0

114.0

s3 mo

n00

t:ó

An exclusive service of Cowan Publishing Corp. by special arrangement with John F. Rider, Publisher

TN1 n.N.le V203

3.14 I.F. 6cB6

V301B AEG AMP. V2 sue

w

ue

7101

Trwi11

' . tSeY.ó:..

T

1001.

10. óñtw 1oov Tav.

4.111. °r

L1302 DEFLECTION

YOKE

10f 0

0.03 11

1110 T

470

ne

w

r4.. r t

01

yi-N = 00

V601 NDR OSG 65N70T

0.4

r.NJ( ° INN

J Ìt0ó

1á:w0! Root 0 ue

V ' "ü 0i-ioe Y

423

PRODUCTION CHANGE NOTES The above schematic is correct for chassis coded "CX-38 R-2". Chassis coded "CX-38 R-1" do not contain the following changes: (1) To eliminate the possibility of "blocking" in the 3rd

I -F. A. R229 (10K, 'ÌW, 10%) was added between ter-

minal "C" of T201 and the junction of L202, R214 and C211. Previously terminal "C" was connected directly to this junction.

V602 NOR. OUTPUT

r10 v rN.i .o[ 6CÚ6 at 6B06GA

e.o

N11

4.tl

3040

rol

11u.7 R°

T .b 118.11 17

-3.r

7.01

1.

{NIT 0111. .11.111, 1010

NWT

J .rar O.

5503 H.V. RECT.

1B36T

INI eó

4011

f

ocep lt... 4001 *

5204 V0EO AMP.

121177

F. 7 OF 1104 1001

4 ?"IC

V205 PICTURE TUBE

I?LP4 N 2IZP4A o" B

4.1

/wn..ru. n r w mN..e.ONNon.

1.1

MM. + m`

V301A SOUND LF.

ew I/2 SUS 13

rr

Tow

31

c3ro

V302 AUDIO DETECTOR

.Nt SONS

Ti w

V303 AUDIO OUTPUT

OBES el v 130.

4001 N

N.a JI

Ìo311= "re

Ott . o ---0 -O--éNá3W

TO"aeart.x

rmR

6CU6

6B06GA

13111.

CURRENT DIS RIBUTION DIAGRAM (NO SIGNAL)

w ero.

ttN

r. M

rt ëw

N

V604 DAMPER

.a

6W4ß7

uer

B. C217 (47mmf Tubular Ceramic) was added in parallel with R229.

(2) To eliminate the possibility of "blocking" in the Video Amplifier. A. R240 (15K, 2W, 10%) was added from pin 8 of

V204 to +300V. R219 (33K, 1W, 10%) which was connected from pin 8 to +260V was deleted.

B. R241 (3.9K, }¡,W, 10%) was added from pin 8 of V204 to +135V. R702 (33K, 2W, 10%) which was connected from +135V to +300V was deleted.

Ns11 M M

Sr3N a. nN C. vs . w. w t 11.0

V701 RECTIFIER

slot SU4G

rra

tN

MEW

N..r. 1,st.

a... :30.

410.

TY.1NT.3aellte11ú0 DCL1:él"11"i110"A :ñN:Nigl:a0el 1

.1.10, i ó:n C00111111.. 0 " 0

MUM.

.

ewi11éùo NO 000 íi N COLOR.... TO e0.10 COR. Or nt O MO.

rr oO.OR

OR MT. ".ñ11n T..e iiai 0iiN OR

T11R0.11111.i IYl.ns ...ielne OP 0011. T ó.ó .I,.N...r. TN 0YU 1

gº,.N.tlTwroIrOriN.R ii TON L0011TOM

I.NT O EL« TONe.1, C ñ ..". .11e11 TN. rna 0 11.3.0....0.13.

aiiéi u.lr.uawasl nT11 vxreanr o nurut11r cï Of ó.ñ`T:iáïu.wr.

u., 1000 010.010L. OR ..un11 0i1wu. .0 °a.iiw. u.urn° n NR"u 3

TONI,O.cO ["V"110 n Oaraci0 TO.

lao a+ 11.110. N

0... úi.a 1.11 rowmOi e11"u.ra


Capehart CX-38 Series An exclusive service of Cowan Publishing Corp. by special arrangement with John F. Rider, Publisher

O

o n '(lIDTH n T-602

o u 3

HORIZ. DRIVE

C-617

R-513 VERT. LIN.

REAR PANEL

3 2 1

PIA. LOCK

ó b

S-01

C 03 01 0.02

jfQUAD.

COIL AOC DIPF.

L 307 J -70I

A.C. R:.CáPTACLD

I -

MOISE =-' REJECT R-310

3 2 1

R. SII

'HEIGHT

1 ' I

l' I

1 Q I

±I . L

D \ C704

O

4

/ O

C701

4

L-60

L-701

FIL'T::R CHOSE

DI

Ts -4

1 T

10

3

V001 (63N7) H0:1Ii.. OSC.

V-11

TUNER PLUG

V101 (

'-F .::.PLLrI2.R

VHF

TUNER

V102 (608) :.IÁIiR

CILL1':OR

r UHF

TUNER

V1 (6A74/674) COCILLITOR

C2-3 CHASSIS

r

O

V602 (6006)

HORI'UOOIAL OUTPUT I V-6

'2604 (644G1) DAMPER

V-9

59.7 rC TRAP

O s v -IS

L.201 (47.251.2)4

Í<1f e0

D C O./2>sU V201 (6CB6) T-202 let VIDEO I -F

Ts -IS

0 r-rlrTr_r=7r-r=-i

TN -IS

D

D

S

4

DI

p6

HORIZONi'AL OUTFJP tRANS.

T-601 ')

000

V202 (6CB6) 2nd VIDEO I-_'

(42.91:C) p (45.0LC) (41.231:W)/h \ 47.2JL'C)

0r ; /,p ,I 53 0: : o P-

0D D0 f V- u O T-201 O

Te -14

felli5:112kielliWI, 5 3 2 1 e 6 5 3 2

- DENOTES TRAP FREQUENCY ADJUST FROM TOP OF CHASSIS

VERT. HOW

MK 2AItL

T-302 AUDIO OUTPUT TRANS.

JL

TN -2

3

4

V302 (6026) DETSCTOR v-3

L-301

u V901 (6U8)V 4

6

7

e

TB 6

30 3

4 a

a

4

SOUI:D -F AOC 0612.

4

9r I

T. 01

I SOUND l ] 'TA5-OPF

2

TS -

3

4

S

6

/ I I S

CONTRAST

2-221

., .

'v701 (5U4) L. V. 1LCTI'11:'-1

0 o

3

e 05 \ \o 6

T - 701

PUTER 0101570610V

SPJ.Y,1:'. 3071TY

J-302

V204 (12BY7)

V203 (6096) VIDEO ALP.

Ira VIDEO I -P 715-13

( 44.11.:0 )

06 oÓ0

T-203

V303 (6BIr5) Ain /0 OUTPUT

I2 J ÌS\ II 61

BRILLIANCE

N -222

V17

3

TONE

-313

A

4

S

6

7

e

0

0

0

0

V 16

Te -II

V701 5U4

1701

T501

V501 6BF6

V303 6BK5

V502 6V6

V602 6CU6

V-12 o loEcl 2 S

3 C704

V501 (613F6) VERT. OBC. AGC CIA;.:P

Te -12

T- S01 VERT.

0u.PU. 'MANS. ó 8 0

6 L;1 6

7502 (696) VIM. OUTPUT

R-313 03E0 ORLI OI DE LISE CHASSIS TONE CONTROL I

"CX-38" CHASSIS LAYOUT - BOTTOM VIEW

t. o ,7

S- 701 ON - OFF

N- 311

V604 6W4

V601 6SN7

C703

1601

V402 12A07

V401 6CS6

CHASSIS LAYOUT

V603 (IN H.V. CAGE) 1B3

V204 f V602 128Y7 .,,.. 6CU6

V301 \\ V604 6U8 V302 6W4

6BN6

1602

CR201 T203 V203 1 V202 V201 INSIDE CAN 6CB6 T201 6CB6 1202 6CB6 T204

C617 T601

R513

T204 V201,V202 L201 6FB6 R502 6CB6

T201 R222

1701

C704

C703

V601 65N7

AC RECPT. AGC

R408 L307 DIFF.

V<02 12AU7

1601 HORZ. RINGING

COIL

V101 6BZ7

V102 6U8

V1

6T4 OR 6AF4

V401 6CS6

R511

TOP VIEW

V302 6BN6

L301

V301 6U8

V701 5U4

1302

R221

T301

V204 12BY7

V501 68F6

T203

V303 6BK5

v50: 6V6

1302

R311

BOTTOM VIEW

An exclusive service of Cowan Publishing Cory. by special arrangement with John F. Rider, Publisher

R-410, 413, 241 2.9K Ohm 3229-392

R-217 4.7K Ohm 3229-472 R-610 8.2K Ohm 1w 10% 3232-822 R-416, 503,

615, 225, 412, 229 10K Ohm 3229-103

R-505 12K Ohm 3229-123 R-617 12K Ohm 2w 10% 3235-123 R-230, 216 15K Ohm 'w 5% 3228-153 R-240 15X Ohm 2w 10% 3235-153 R-205, 212,

603, 411 22K Ohm 3229-223 R-407, 304 22K Ohm 1w 10% 3232-223 R-203 24K Ohm Vzw 5% 3228-243 R-231 27K Ohm Ihw 5% 3228-273 R-515 33K Ohm 3229-333 R-219 33K Ohm 1w 10% 3232-333 R-702 33K Ohm 2w 10% 3235-333 R-220 39K Ohm 3229-393 R-301, 507 56K Ohm 3229-563 R-302, 514 56K Ohm 1w 10% 3232-563 R-613 68K Ohm 3229-683 R-604, 605 22K Ohm 3229-823 R-601 82K Ohm 1w 10% 3232-823 R-235, 506,

606, 707 100K Ohm 3229-104 R-504, 612 120K Ohm 3229-124 R-708 180K Ohm 3229-184 R-206, 210,

403, 223 220K Ohm %w 5% .3228-224 R-303, 701 330K Ohm 3229-334 R-406, 417,

501 470K Ohm 3229-474 R-404, 420 560K Ohm 3229-564 R-510 820K Ohm 3229-824 R-616 1 Meg Ohm 3229-105 R-620 1 Meg Ohm 1w 20% 453477A-1 R-512, 405,

607 2.2 Meg Ohm 3229-225 R-415 2.7 Meg. Ohm 3229-275 R-402 5.6 Meg. Ohm 3229-565

Transformers & Inductances Ref. No. Description Parts No. T-701 Power Transformer 850300B-3 T-601 H.V. Transformer 850285D-1 T-602 Width Transformer 650589B-1 T-501 Vert. Output Transformer....750354C-2 T-301 4.5 MC I.F. Transformer 650929A-1 T-302 Audio Output Transformer.. 650216A-3 T-204 I.F. Coil 750460C-1 T-203 Detector Transformer 750468D-1 T-202 1st I.F. Transformer 750462D-1 T-201 2nd I.F. Transformer 750461D-1 L-701 Filter Choke 650215A-5 L-601 Horiz. Osc. Ringing Coil 650637B-1 L-602 Yoke 850221C-2 L-301 4.5 MC Sound 650638B-1 L-302 Quadrature Coil 650776A-1 L-201 39.75 MC Trap 650948A-1 L-202 2.2 mh. choke 450338A-4 L-206 150 mh. Peaking Coil 750597A-1 L-207 10 mf. RF Choke 450338A-5 L-212 140 mh. Peaking Coil 750597A-2 L-213 100 mh. Peaking Coil 750597A-3 L-214 200 mh. Peaking Coil 750597A-4

Capacitors Ceramic Capacitors Rated at 500 V

Unless Specified Otherwise C-304, 308 .3.3 nmfd 650030A-5 C-310 10 mmfd 650030A-18 C-227 27 mmfd 2271-9022 C-208, 218,

302 47 mmfd 650030A-17 C-202, 210,

211 470 mmfd 450469A-11 LC -206 .470 mmfd (Dual) 650858A-1

C-621 500 mmfd 20 KV 650153B-2 C-201, 203, 1000 mmfd GMV 450469A-5

214, 226 C-306 1000 mmfd 450469A-7 C-205, 213 1000 mmfd (Dual) 600881A-9 C-402 1500 mmfd GMV 600881A-5 C708A & B 1500 mmfd (Dual) 453521A-4 C-225 5000 mmfd 450469A-12 C-305, 307,

311, 312 315 10000 mmfd 600881A-8

All Mica Capacitors Rated at 500V Unless Specified Otherwise

C-603 47 mmfd C-626 100 mmfd C-604 270 mmfd C-615 330 mmfd C-502, 613 390 mmfd C-212, 605,

606, 611, 614 470 mmfd

C-612 4700 mmfd All Tubular Capacitors Are Rated at 20% Unless Specified Otherwise

2272-21470 2272-21101 2272-21271 2272-21331 2272-23391

2272A1471 2272-43472

C-501, 602 001-600V C-601, 607 0022-600V C-506 0027-1000V 10% C-313 01-406V C-406, 505 01-200V C-510 022-400V

2248-1020 2248-2220 2249-2729 2247-1030 2246-1030 2247-2230

C-512, 513, 610 022-200V

C-503 033-600V 10% C-620 047-600V C-403 047-400V

2246-2230 2248-3339 2248-4730 2247-4730 2246-6839 2248-1040 2247-1040 2246-1040

C-504 068-200V 10% C-220, 507 1-600V C-222, 404 1-400V C-624 1-200V C-405, 622,

623 C-407,410

Eleetrolytics Ref. No. C-219 C -703A -B -C -D C -704A -B -C -D

R-311 R-221 Contrast Control R-222 Brilliance Control R-502 Vert. Hold Control R-614 Horiz. Hold Control R-408, 511... Height & Pix Lock Control R-513 Vert. Linearity Control R-310 Noise Rejection Control

.22-400V 2247-2240 22-200V 2246-2240

Description Parts No. .8 mfd-250V 650228A-13 50, 40, 30, 20 mfd-400V 750090B-42 50 mfd-400V, 20 mfd-200V, 750090B-41

100 mfd-150V, 25 mfd-25V.

F-701 F-601 PC -401

Off -On -Vol. Control 650928A-1 650927A-1 453328A-3 453466A-1 453328A-2 .650777A-1 650642A-3 650642A-5

Miscellaneous UHF RF Unit VHF RF Unit Ion Trap Focuser Width Transformer's

Tuning Core 3AG 125V 500 MA Fuse 3AG 125V 200 MA Fuse Vertical Integrator

750593A-1 850330A-1 650276A-5 850291A-1

453118A-1 450317A-16 450183A-2 453214A-1

Picture Tube Socket 650596C-6 J-302 Speaker Connector 450972A-2 C-617 Horiz. Drive Trimmer

(40-450) 450527B-1 452729A-1 453639A-1 452580A-2

Antennae Binding Post 650972A-1 Tuner Connector 650971A -G1

S-401 AGC Differential Switch Fuse Block

J-701 Interlock Receptacle


IN. H.V. CAGE

2 AM,

°ä.U°41 111 é_

1 lW5 ROI SNORIING d». NpM2. RINGING

COII

.S AMR elO-el

VERTICAL HOLD

HORIZONTAL HOLD

BRILLIA

UHF OSCILLATOR

ADJUSTMENTS VHF TUNER

Capehart

CHANNEL LIGHT

INDICATOR

UHF TUNING

VHF CHANNEL SELECTOR

VHF FINE TUNING

WIDTH CONTROL

CX-38 Series

BEAM CORRECTOR

MAGNET

A CENTERING HANDLE

ION TRAP

FOCUS ADJUSTMENT

FOCUSER

NOISE REJ. CONTROL

HEIGHT CONTROL

,la

QUADRATURE COIL

AGC DIFF. SWITCH

`'AC RECEPTACLE

PIC LOCK

VERT. LIN. CONTROL

HORIZ. DRIVE CONTROL

CAPEHART CX-38 SERIES TV CHASSIS

REPLACEMENT PARTS PRICE LIST

Resistors All Resistors Are t/2 w 10% Unless Specified Otherwise

Ref. No. Description Parts No. R-705 270 Ohm 2w 10% R-621 6.8 Ohm 650101A-22 R-622 470 Ohm 1/aw 20% R-238 39 Ohm 3229-390 R-706 470 Ohm 1w 10% R-204, 211,

825 47 Ohm 3229-470 R-305 R-202

680 Ohm 1K Ohm 34w 20%

R-207, 213 100 Ohm 20% %w 20% 3230-101 R-611 1.2K Ohm R-214 120 Ohm 3229-121 R-236 2.2K Ohm R-307 150 Ohm 3229-151 R-233 2.2K Ohm 2w 10% R-704 150 Ohm 2w 10% 3235-151 R-237 2.7K Ohm R-618 180 Ohm 4w 10% 650101A-25 R-208 3.3K Ohm R-312 220 Ohm 3229-221 R-226, 227......3.3K Ohm 2w 10%

3235-271 3230-471 3232-471 3229-681 3230-102 3229-122 3229-222 3235-222 3229-272 3229-332 3235-332

the KEY /I

in MULTIMETERS

to your problem metal -cased pha©stron I the NEW L

POCKET SIZE WITH A 41/8" LENGTH SCALE

WE LEAVE IT TO YOU WOULD YOU BUY A PLASTIC -CASED WRIST WATCH .. .

if you could buy the finest movement in a magnetically shielded metal case?

Phaostron, world famous manufacturer of ENVIRON- MENT FREE PRECISION AIRCRAFT EQUIPMENT for Mili- tary and Industrial uses introduces a new concept in Multimeters. This magnetically shielded, metal -cased "555" compares with plastic -cased multimeters as a fine watch in a precious metal case would compare with a plastic wrist watch.

The shielded, shatterproof and anti -magnetic case insures continued accuracy and integrity of this instrument for years to come.

Phaostron "555" Multimeter incorporates more ranges, including AC current, greater visibility, simplified and functional controls and the greatest value offered to date.

See the Phaostron "555", note its many outstanding features, its beautiful satin chrome case, its compact- ness and light weight, and you will know why

"YOU CANNOT BUY BETTER"

AC CURRENT RANGES SEPARATE RANGE & FUNCTION SWITCHES

ONLY 2 JACKS

COLOR CODED SCALES ARE RED, GREEN, BLUE & BLACK

ACCURACY 3% DC, 4% AC

GENUINE LEATHER CARRYING CASE

$ 5.95

PANEL MOUNTING ADAPTER $1.50

"555" MULTIMETER

$39 95 at your PARTS DISTRIBUTOR complete with probes and batteries

Manufactured by PHA 0 S T R 0 N COMPANY 151 Pasadena Avenue South Pasadena, Calif., U.S.A.


IJLQU4E - WAVE GENEPATOk

PART 1

by OSCAR FISCH

L1J`I.iiLi.g

IT would be generally agreed, in the the opinion of the author, that the

square wave generator is not a familiar piece of test equipment to the average serviceman. At the present time, there are very few shops equipped with a generator of this type. A few manufacturers of test equipment have added the square wave generator to their line in recent years. Basically, this generator is used to check frequency response and phase distortion in wide band amplifiers, such as those found in high fidelity audio amplifiers and in TV video amplifiers. It may also be used, incidentally, as a bar generator for ad- justing horizontal and vertical linearity. In most cases, a switch is provided to give a sine wave rather than a square wave output. This permits the use of

+100

7 e.0

B

A;

B B"

c Z/ 5o

--- I

/ \

l

- /

\

\ i 1/co \ / >

TIME W I

\`' \ / (Sec.)

-100 '

Fig. I - Comparison of sine and square waves.

the instrument in making accurate quantitative measurements of the frequency characteristics of an amplifier. These applications will be discussed in more detail later, and are mentioned briefly here simply to give an idea of what may be expected of the square wave generator. Since understanding goes hand in hand with the intelligent use of such a device, it is the purpose of this article to explain the basic principles involved in square wave testing.

Makeup of Square Wave It will be necessary at the outset to

examine the makeup and the characteristics of a square wave. In Fig. 1, the solid line represents a square wave of voltage having an amplitude of 100 volts, and a frequency of 60 cps. The dashed line represents a familiar sine wave ac voltage having the same amplitude and the same frequency. These are both ac waves of voltage but there is one obvious and essential difference between the two. In the sine wave, the voltage rises gradually from zero at A to its maximum value at B, and then falls gradually back to zero at C. In the square wave, however, the voltage rises very rapidly from zero at A to its maximum value of 100 volts at B', remains at this value for almost half the cycle and then rapidly drops back to zero, or from B" to C on the diagram.

A similar variation in voltage takes place during the negative half cycle. The reason that the time taken from B' to B" is almost, but not quite, a half cycle is that the rise in voltage from A to B' and the fall from B" to C are not instantaneous but do take up a small amount of time.

Why is a square wave of such importance? The answer lies first in the fact that a square wave may be considered to be made up of an infinite number of sine waves, starting with the fundamental, and including all the odd

B

+30 E

+20

- +10

0

Lu -10

-20

-30

FUNDAMENTAL 100 CPS

EQUIVALENT WAVE 100 CPS

3rd. HARMONIC 300 CPS

T TIME

A

Fig. 2-Combination of fundamenta and 3rd harmonic as the first step in the synthesis of the square wave.


OFUNDAMENTAL + 3nl. kAr?.MONIC

I FUNDAMENTAL + 3, -. 1R- MONIÇ + 5th. HARMONn.

+30

+20

+10

5th. HARMONIC

Fig. 3 - Closer approach to truer square wave is observed as addition-

al harmonics are added.

harmonics. Secondly, in passing through the various circuits of an amplifier, even though the square wave appears to be a single wave, it behaves just as if all of the harmonic frequencies of which it is composed are going through the amplifier simultaneously. In a theoretically perfect amplifier, all of these frequencies would be amplified equally, and they would all maintain the same phase relationships with each other so that their combination at the output would result in a square wave having the same shape as that which entered at the input, except of course for its increase, in amplitude. By comparing the wave shape of the output with that of the square wave input, and inter- preting any differences, defects in the amplifier may be diagnosed.

It was stated in the preceding paragraph that a square wave may be considered to be made up of an infinite number of sine waves, starting with the fundamental and including all the odd harmonics. To be more specific, suppose a theoretically perfect square wave had a frequency of 100 cps. The math- ematics of square wave analysis shows that this square wave would contain the following sine wave components.

Fig. 4-Equivalent voltage obtained when 3rd, 5th, and 7th harmonics are

combined with the fundamental.

a) A fundamental whose frequency is the same as that of the square wave, namely, 100 cps, and whose amplitude depends on the amplitude of the square wave.

b) A third harmonic (300 cps) whose amplitude is 1/3 .the amplitude of the fundamental.

c) A fifth harmonic (500 cps) whose amplitude is 1/5 the amplitude of the fundamental.

d) And so on down the line for the 7th, 9th, 11th, etc., etc., harmonics. To further clarify this concept, suppose we examine what happens when we combine these harmonics graph- ically. In Fig. 2, the dashed line represents the fundamental of 100 cps, and the light line represents the 3rd harmonic, the amplitude of which you will notice is 1/3 the amplitude of the fundamental. To find the curve of voltage which is the equivalent of these two acting simultaneously, the following procedure is used.

SQUARE -WAVE GENERATOR

AMPLIFIER UNDER TEST

OSCILLO- SCOPE

Fig. 5-Block diagram of test set-up for square wave testing of an am-

plifier.

1. Select any point along the time axis such as t1.

2. Draw a light line perpendicular to this axis at the selected time t1. This would be the line AB.

3. At this time, the voltage contributed by the fundamental is the voltage at point D/or +15 volts. The voltage contributed by the 3rd harmonic is the voltage at point C, or +10 volts.

4. Combining these two gives a resultant voltage of +25 volts. Thus, at the time selected, the equivalent voltage is +25. This locates point E, on the t, line and 25 volts above the axis. A similar procedure would show that at t, the contributing voltages are +30 from the fundamental and -10 from the 3rd harmonic, giving a resultant of +20, as indicated by F of Fig. 2.

Points E and F therefore are. two points on the curve of voltage which represents the combination of fundamental and third harmonics. By following the same procedure for many other points along the time base, the curve of voltage indicated by the heavy solid line would be obtained.

SIGNAL GENERATOR

The Precision Model E-300 Sine and Square Wave Generator is a typical

commercial product.

In Fig. 3, the dotted line is simply a repetition of the solid line curve of Fig. 2, and represents, as noted previously, the combination of a fundamental and a third harmonic with 1/3 the amplitude of the fundamental. Of course this is a far cry from a square wave, but it is certainly closer to a square wave than fundamental sine wave we started with. Its sides are steeper, and in spite of the dip at the center, the top is beginning to flatten out.

The light solid line in Fig. 3 represents the fifth harmonic of the fundamental, with an amplitude one fifth that of the fundamental. Without re peating the details, curves A and B in this figure may be combined by the same procedure previously outlined for the combination of the fundamental and 3rd harmonic. The result would be the curve shown by the heavy solid line of Fig. 3. When the 7th harmonic is added to this, Fig. 4 results. Com- paring Figs. 2, 3, and 4 indicates that:

1. As these odd harmonics are added, the sides of the wave get steeper.

2. At the same time the top of the wave gets flatter in the sense that, although the number of ripples gets larger, the amplitude of these ripples gets smaller.

With this as a basis, it should not be difficult to accept the fact, previously mentioned, that if an infinite


TIME

Fig. 6-Output of an amplifier with poor low frequency response, when

input is a square wave.


Do you have a vexing problem on the repair of some radio or TV set? If so, send it in to the Answer Man, care of this magazine. All inquiries acknowledged and answered.

Note: Only communications with Radio-TV Service Firm letterheads will be considered and answered. Please indicate make, model, and chassis number of receiver.

Dear Answerman: I have an Admiral 21F 1 chassis in

which I am unable to make the vertical oscillator circuit function. 'When I got the receiver I realized that some other technician had been working on it because condensers and resistors were hanging loose. During the course of rewiring in accordance with the schematic I found that the screen resistor feeding the horizontal output tube had burned open. A new resistor was installed thereby providing horizontal sweep and high voltage. However, I could not get vertical deflection and I since have been unable to locate the cause of this trouble. All components in the vertical oscillator circuit have been thoroughly checked and the oscillator transformer and tube has been replaced without success. The voltages in the oscillator circuit are about normal but there is no waveform developed to drive the output stage. This has been determined with a scope. Do you have any idea that might be of help?

D. S. Floral Park, L.I.

On examining the schematic diagram of the Admiral 21F1 chassis of a widely distributed schematic publisher it is found that the vertical oscillator circuit has a mistake in it. In checking other published schematics of the same chassis it is found that this error has been duplicated.

Figure 1 shows the partial schematic for the vertical deflection system with the incorrect connection of the .047 uf charging condenser and its 8.2K peaking resistor. This condenser -resistor

Incorrect Connection

Correct Connection-, \, VERTICAL OUTPUT

%2 6SN7 `,, `,TUBE GRID

0047

1

INTEGRATOR

NETWORK

1MEG VERTICAL

HOLD

150 K

1.2 MEG.

7-7

0406 .047

820011

_HEIGHT 2.5 MEG.

Bt

Fig. I - The correct connection for the vertical oscillator charging condenser and peaking resistor in the

Admiral 21 FI.

combination, when connected to the vertical output tube grid side of the .1 uf coupling condenser does not permit the development of a sawtooth voltage.

The condenser -resistor circuit must be connected to the plate circuit of the vertical oscillator tube as shown in the dashed lines of Fig. 1. Only in this fashion will the electrons be removed from the top plate of C406 during the period when the vertical oscillator tube is being held at cut-off by the grid bias. These electrons flow from the top side of the condenser through the 1 meg resistor and the 2.5 meg height control to B plus. During the removal of these

electrons from the one side of the condenser a sawtooth voltage is developed across it, this voltage being coupled to the vertical output tube causing vertical deflection. Just before the sync pulse comes along, the negative bias developed in the grid circuit has been decreased by discharge of electrons from the C405 through the transformer and the grid leak resistors. With the sync pulse the tube is triggered into conduction and provides a discharge path for the voltage developed across the charging condenser C406; and the next sawtooth begins.

Understanding the circuit operation makes it possible to pick out mistakes in schematic such as above. In the pre- paration of service literature it is im- possible to prevent errors from occurring. If this does happen it takes a rather informed technician to spot the trouble.

Dear Mr. Answerman: I have three television receivers with

picture tubes that arc in the neck between the elements.

Does the arcing mean that the picture tubes are defective or could some circuit defect cause the arcing. If so, what could possibly do this? The sets work okay otherwise.

P. K. Madison, Pa.

Arcing or flashing in the neck of picture tubes is commonly caused by particles lodging in the electron gun. It usually is visible just forward of the ion trap. Flourescent material from the coating of the inside face of the tube loosened during transportation or manufacture may have caught in the electron gun structure. These particles can intermittently short the high voltage anode to other elements.

Often, after a period of operation of a new picture tube, the particles burn themselves open without steps having to be taken for their removal.

In some cases the accumulation of the particles may be so great as to cause a complete short between two elements such as the cathode and grid or between the filament and cathode. In such cases the picture signal is shorted out or the background or brightness control of the picture is made inoperative. In any event, it is very unlikely that some circuit defect will cause this type of difficulty as it usually is solely a picture tube problem.

However, the condition does not necessarily mean that the picture tube must be replaced. Many cases of arcing can be corrected by either of two possible methods.*

1. These particles lodged in the gun structure can frequently be loosened by



Radio-TV Service Dealer Videe Speed SiS'euLieit9.lem40 Data Sheets

................ ................. ................ ................. ................ ................. ................ .................

ti

Mfr: Fada Model S1055

Card No: FAS55-1

Section Affected: Raster

Symptom: No high voltage

Cause: Shorted condenser in horizontal discharge circuit

What to Do:

Replace: C49 (390 µµf)

Mfr: Fada Model 51055

Card No: FAS55-2

Section Affected: Pix

Symptom: No video

Cause: Shorted video screen condenser What to Do:

Replace: C20C (10 µf)


Card No: FAS55-3

Section Affected: Sync

Symptom: Critical horizontal hold

Cause: Leaky condenser in phase detector

What to Do:

Replace: C39 (.05 ¡if)

V8 6ÁG7

VIDEO OUTPUT

B+

37

Radio-TV Service Dealer Video speed sue: y. s.tem40 Data Sheets


Card No: FAS55-4

Section Affected: Pix

Symptom: Video overload on normal contrast control settings

Cause: Leaky coupling condenser

What to Do:

Replace: C4 (120 µµf)


Card No: FAS55-5

Section Affected: Sync

Symptom: Vertical hold drifts out of range

Cause: Vertical oscillator resistor increases in value

What to Do:

Replace: R56 (1.5 meg)


Card No: FAS55-6

Section Affected: Sound & pix

Symptom: No sound or pix

Cause: Open voltage divider

What to Do:

Replace: R87 (1750 ohms -20W)

............... ................


TV FIELD SERVICE

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a Miniolu'u

Vo/I - Ohmmeter

by Edward McArdle

THE current crop of new test equipment produces a unique volt -ohm-

meter from the standpoint of utility and circuitry. This instrument is the Simp- son Midgetester Model 355 shown above. It is so small that it actually can be carried in your shirtpocket. Its measurements are 23/4" x 41/2" x 1" overall.

What It Does This instrument functions as a 5 -

range dc voltmeter, a 5 -range ac voltmeter, and a 4 -range ohmmeter. Func- tion switching, that is from an ac voltmeter to a dc voltmeter, to an ohmmeter, is accomplished by small switches located

60K TO 500K NNl1l A.C. CAL.

MOV T 78.uÁ

1535. WITH SERIES +

it -

10K

1 NyyW OHMMETER ZERO

ADJUSTMENT

-DCV

under the tip jacks marked ACV+, -DCV, and OHMS. These switches are closed by screwing the black test lead into any of the above mentioned tip jacks. The red test lead is then screwed into the tip jack providing the desired range.

Ohmmeter The circuit diagram of the instrument

is shown in Fig. 1. As an ohmmeter the ohms switch is depressed by inserting the black lead into the OHMS tip jack. Assuming that the xl range is used, shorting the test leads inserted into the aforementioned tip jacks does two things. First, it connects a 120 ohm resistor

1 28,500 90K

1.5V

T

OHMS

ALL SWITCHES NORMALLY OPEN

480K 2.4MEG. 9ME6.

3V 12v GOV 300V 1200V

5455 'VV/w

10021A SHUNT

120 1080 10.8K

O RI RIO R100

107K 15V

- R x 1000

Fig. 1-Circuit diagram of Simpson Midgetester Model 355.

across the battery. Second it provides a

voltage for the meter circuit which is adjusted to full scale (78 microamperes) by the Ohmmeter Zero Adjustment po- tentiometer, the knob of which is lo-

cated in a recessed pocket on the right side of the instrument.

If the test lead short across OHMS and xl is removed and an external 120 ohm resistor connected across the leads the meter will read half scale because half the battery voltage is now made available for the ohmmeter. This half scale reading is calibrated as the 120 ohm reading of the xl scale ohmmeter. By simple ohms law calculations the other ohms scale readings may be similarly derived.

The ohms ranges provided by xl, x10, x100 use a 1.5 volt battery (Bur- gess Battery Co. Type Z), and the x1000 ohms range uses an Eveready Type 404E 15 volt battery. These range provide useable readings of resistance values from 1 ohm to 10,000,000 ohms.

DC Voltmeter For dc voltage measurements the

black probe is screwed into the -DCV tip jack. This depresses the switch indicated by the dashed line which shunts the 78 microampere meter with a 5455 ohm resistor. The latter draws 22 microamperes so that the entire meter becomes a 100 microampere meter which is

equivalent to a 10,000 ohms per volt meter.

Five dc voltage ranges are provided. When using a voltmeter the service technician must be sure the instrument does not unduly load down the circuit under test. To calculate the loading effect in ohms of any range of this instrument one merely multiplies the voltage range



TRADE FLASHES [from page 6]

award of the Gano Dunn medal. Estab- lished this year, the medal will be awarded annually to an alumnus of the Cooper Union for outstanding professional achievement. Mr. Dubilier is be-

ing honored by his Alma Mater for his inventions and development of high voltage condensers, or capacitors, an important element which helped the tremendous growth of the electrical and electronic industries.

Blonder -Tongue Labs, Inc. of West- field, New Jersey has put into full op-

eration its second plant located in Newark, N. J., providing over 30,000 square feet of additional manufacturing space.

The new Blonder -Tongue plant is

now fully equipped and staffed with qualified technical and production per- sonnel to do contract manufacturing of all types of commercial electronic equipment.

A new dealer finance program, providing for both dealer inventory and retail sales financing to be underwrit- ten by Raytheon Manufacturing Com- pany in conjunction with the dealer's local has been announced. The pro -

Better sound from 3XFORD SPEAKERS . .

complete line fram2'to15"... for all replacement needs . . .

ORDER TODAY!

OXFORD OXFORD ELECTRIC CORPORATION 3911 South Michigan Aver Le Cbicog 15, Illino s

EXP:RT- R)B4FN AGENCIES, NEW CORK CITY IN CANADA - ATtA, RADIO C)RF its., TORONTO

gram contains a complete manufacturer's obligation to repurchase any repossessed merchandise.

H. Ward Zimmer, at the age of 57, died on January 28 at the New York Hospital after a brief illness. Mr. Zim- mer was President of Sylvania Electric Products, Inc., and a pioneer in the electronics industry.

A television receiver specifically designed to operate on both direct current and alternating current without the use

of an inverter or converter has just been introduced by Emerson Radio and Phonograph Corporation, it was announced yesterday by Michael Kory, Director of Sales.

ASSOCIATIONS [from page 16]

was honored to have as its guest in charge of the educational program, Donald Landis of the local Naval Ord- nance Plant. Mr. Landis is an electronics engineer and well qualified in the field of TV service.

Radio-TV Service Association of St. Paul, Inc.

First Annual Banquet of Radio -Tele- vision Service Association of Saint Paul, Inc., was held January 12, 1954 at the Officers Club, Fort Snelling St. Paul, Minn. Local television and radio stations will furnish entertainment after ¡the banquet. Facilities were provided and 400 people were in attendance.

New Officers for 1955 who were in-

stalled at this banquet are as follows: President-Clyde Orlando Vice President-Harry Winkler Treasurer-Robert Rohweder Secretary-Ross Hilker Asst. Treas.-Joe Driscoll Asst. Secv.-Clarence Thoele Board Member-Jim Dorfsman.

New Hampshire Radio & TV Association

Harvey O'Dowd of Goffstown was reelected president of the New Hampshire Radio and Television Association, a servicing organization, at the annual meeting in the New Hampshire Technical Institute here.

Other officers elected were Paul Frost of Concord, first vice-president; George Bennett, Manchester, second vice-president; Ernest Tetrault, Manchester, treasurer; Emile R. Gelinas, Manchester, executive -secretary, and Warren Davis, Hampton, secretary.

Horace Bradford of Laconia; George Hill and Earl Whittemore of Keene;


John Condon and Henry Cantin, Man- chester, were named directors.

TV Installation Service Association -Illinois

At the annual election meeting of the Television Installation Service Associa- tion the following officers were elected for 1955: Frank J. Moch of Aide Serv- ice Corp. was reelected President unan- imously. Elected to serve with him for 1955 were Walt Krzak of Television Engineers, Inc., 1st Vice President: Russ Havill of Havill's TV, 2nd Vice Presi- dent; Larry Corlew of Electronic En- gineers, Inc., Secretary; George Hingson of Courtesy TV Service, Treasurer; and Mel Brown of B & M Radio & TV Serv- ice Sargeant at Arms.

Calling North Carolina Associations

Readers in the Clarkston, N.C. area would like to know of any service association meeting hereabouts. Associations please write in forwarding address to Editor. Thanks.

R.A.T.E.T. Assn. Inc. (N. Y.)

Lectures this year will be held at The Cornish Arms Hotel. Zenith Radio Corp. of N. Y. will give a lecture on March 24, on the new Zenith chassis- Troubleshooting, alignment, etc. In April JFD Manufacturing Co., Inc. will give a lecture on new TV antenna and new installation accessory developments. Emerson Radio & Phonograph Corp. will lecture in May. We anticipate a

series of four color lectures by Sylvania Electric Products Co. in June. After the Summer Vacation RATET will continue this fine program of presenting more of the leading manufacturers to you.

At its last meeting December 16, 1954 the following were elected to hold office during 1955:

President, Charles Vassalo; Vice Pres- ident, Leon Sievers; Secretary, George Saddler; Treasurer, Rudolph Stone; Ed- itor, George Steinburg; Sergeant -at - Arms, Ray Calderon; Registrar, Myron Rawluk; Inter -State Affairs, G. Wager Hill; Chairman of Associate Members, Robert Fenster; Chairman of TV Store Owners, Norman Weston.

Association of TV Service Com- panies, Cincinnati, Ohio

ATSCO observes that Miami, Florida is the scene of the latest activities of the Better Business Bureau, and the District Attorney-nine service company operators have been charged with petty lar- ceny based on false billing of TV service repairs.

Could the reason for this be the low service charges that prevail in Miami?

Centralab P.E.C.* Kits that save time, cut your parts investment

Centralab Plasti-Pak No. PCK-45 gives you a handy shop stock of 45 Printed Electronic Circuits

$24.00 including hinged -lid plastic container suggested net price

With Centrelab's PCK-45, you have at your fingertips the equivalent of a stock of 106 ceramic -based resistors and 133 ceramic capacitors.

You're glad you have this kit, every time you run up against one of the millions of old radio and TV sets that were built before P.E.C.'s were used. Instead of wasting time trying to locate a shorted or intermittent component, you simply replace an entire section of an old-style circuit with a single P.E.C. - and that's that!

That makes sense, doesn't it? You don't replace only one old, worn-out component; you replace all the components of the same age, easily and inexpensively - and you end another service headache.

Centralab's Plasti-Pak No. PCK-45 can be one of the handiest service "tools" you have in your shop. Order one from your Centralab distributor.

Send coupon for Centralab Printed Electronic Circuit Guide No. 3 that shows circuit schematics to help you install P.E.C.'s.

Centralab Plasti-Pak No. PCK-18

$9.00 including hinged -lid plastic container suggested net price

You get 18 Printed Electronic Circuits - nine of the most popular types in ratio to usage. Enough circuit elements to replace 42 old-style resistors and 52 old-style capacitors. Order from your Centralab distributor.

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Quote from a Miami newspaper adver- tisement "No Charges, if TV is not operating to your satisfaction with two or less new tubes. Free Estimate if set requires shop labor." Or from the same newspaper "No Charge, if set is not repaired in your home for under $6.00. Parts included!" or "$1.50 TV Service Call in your home." Just proves the old saying "You can't `give' something for nothing." Be honest with yourself and your customers. Keep your prices at a

level where you can make a reasonable profit. Don't let this happen here!

Long Island Electronic Technicians Assoc., Inc. (N. Y.).

Shown below is Dick Carey, Pres- ident of L.I.E.T.A. 'sweating it out' during the holiday rush season. He at- tributes his success in the servicing busi-

ness to the fact that he belongs to and takes an active part in Association work and Association programs. Mr. Carey has two trucks on the road and keeps four men busy besides himself. He is

one of the old-timers in the business, having had a radio shop in the earliest days.

Syracuse (N. Y.) TV Technician Assn.

STTA in cooperation with ESFETA (Empire State Federation of Electronic Tech. Assoc.) is presenting a lecture series that will benefit all electronic technicians. Be sure you attend these important meetings that will cover the manufacturing and maintenance of new electronic components to be used in present and future design of Radio &

T. V.

TV INSTRUMENT CLINIC

[from page 23]

the fine-tuning control is turned, the frequency of the local oscillator is

varied. In consequence of the local - oscillator frequency change, the i -f output frequency from the mixer changes correspondingly. The first i -f stage gen- erates a certain amount of harmonic signal; when mixer regeneration is pres-

ent, the harmonic signal feeds back from plate to grid of the mixer stage via the plate -grid interelectrode capacitance of the mixer tube. This harmonic signal beats with the incoming r -f signal, and in some cases the beat is in -phase while in other cases the beat is out -of -phase. The phase relations change as the fine- tuning control is turned, and hence the shape of the response curve changes like- wise. Mixer regeneration is usually less in front ends of modern design.

Q. When making a single -stage check in an i -f amplifier, what should be looked for?

Fig. 5-Typical single IF response on a 15 mc sweep.

A. Fig. 5 shows a typical single i- f stage response, displayed on 15 -mc sweep. Note that the bandwidth is large; in this example the bandwidth (measured between the half -voltage points) is greater than 10 mc. In other cases, the bandwidth may be less, perhaps 5 mc. But substantial bandwidth is charac-

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teristic of normal operation, and narrow bandwidths in a single -stage response indicate the presence of regeneration, or open damping resistors. The gain of a

single stage should be about 10 times, at low bias.

Q. Why is sine -wave sweep used in alignment work, rather than sawtooth sweep?

Fig. 6-Difficulty of synchronization is shown above with sine -wave sweep.

A. Synchronization is sometimes a problem when sawtooth sweep is used, as illustrated in Fig. 6.

VOLT -OHMMETER [from page 41J

by 10,000. Thus, the loading effect of the 300 volt range is 300 x 10,000 = 3

megs. A good rule to follow when measuring voltages in high resistance circuits such as agc, is to use the highest possible scale of the instrument that will provide a useful reading.

AC Voltmeter

The ác voltmeter is put into operation by inserting the black probe into the ACV+ tip jack which depresses switch shown by the dashed line. AC voltage measurements are made by rectifying the ac voltage with an internal full wave bridge type instrument rectifier. The resulting dc voltage causes a pro- portional current to flow through the meter. An internal shunt resistor, indi- vidually calibrated to the characteristics of each meter and rectifier, is connected in parallel with the meter and rectifier. The same set of series resistors as were used for dc voltage ranges will increase the total instrument resistance to 10,000 ohms per volt for ac voltage ranges also.

All ac voltages indicated with the Simpson Midgetester Model 355 are rms values based on full wave rectification. If the input voltage is a sine wave, multiply the indicated value by 2.828 for the peak -to -peak value, or by 1.414 for the peak value.

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Phoductä

Brach "Magne-Tenna" A new indoor antenna engineered

and developed by the Brach Manu- facturing Corporation, a Division of the General Bronze Corporation, and trademarked "Magne-Tenna." It measures 14" x 6" x 4" has no pro- truding rods and is enclosed in a decorative cabinet which can be placed on the top of the home TV set. Best pictures are received by simply turning a knob which operates the same as tuning your radio set. For information, write Brach Manufacturing Co., 200 Central Ave., Newark, N. J.

DuMont Oscillograph The DuMont 'Type 324, by Instru-

ment Division; Allen B. DuMont Laboratories, Inc., Clifton. N. J., makes possible accurate d -c measurements of amplitude in the millivolt and microvolt region with excellent stabi'ity and low noise. Full scale amplitude ranges in 16 steps from 4 my full scale to 400 v full scale with balanced input available on 7

ranges. Frequency response flat from dc up to 300 kc, depending on sensitivity range.

TV Replacement Resistors a 5 watt and a 10 watt

ECONOHM RESISTOR which can be stocked without fear of change in value. The only resistors of this type that are wound on ceramic cores, and are impervious to mois- ture. Tinned copper leads are at- tached in a manner eliminating the pos=ibility of stre=ses being trans- mitted to the winding. Inquiries are invited to TRU-OHM PRODUCTS, General Sales Office, 2800 Milwaukee Avenue, Chicago 18, Illinois.

Federal Electronics Filter Federal Electronics of Rockville

Centre, N. Y., announces the "3 -Pi" T.V.I. Filter for the suppression of television interference. The unit features printed circuit design to effectively suppress TV interfer- ences caused by auto ignition systems, medical diathermy and X-ray trieal appliances. For details write: equipment, neon signs, and elec- Federal Electronics, Federal Elec- tronics Building, Rockville Centre, N. Y.

Eico Signal Tracer A new deluxe milti-signal tracer

featuring facilities for RF, IF and audio signal tracing and troubleshooting in AM, FM and TV sets has been produced by EICO (Elec- tronic Instrument Co.,) 84 Withers Street, Brooklyn 11, N. Y. Cataloged as Model 147, it has separate high gain rf and low gain audio input channels, built-in 5" test speaker, and a magic eye monitors both channels for easier estimation of signal strength and gain -per -stage.

Ram Flyback Transformers Ram Electronics Sales Co., Iry-

ington-On-Hudson, New York, announced two horizontal output transformers for replacement in Zenith receivers. Models X070 and X116 feature unique anti -corona spray, special terminal lead distribution and high voltage stand-off construction. An instruction brochure, including circuit diagrams, is supplied with each unit. For further information, writedirectly to Ram.

Aerovox High -Voltage Ceramics To meet the higher operating volt-

ages of color TV receivers, a heavy- duty ribbed -case ceramic capacitor is produced by the Hi -Q Division of Aerovox Corporation, Olean. N. Y. Of particular interest in high -voltage applications is the special ribbed construction which provides an extra -long "creepage path" in a small size. Rated at a working voltage of 30 kvdc, or a test voltage of 50 kvdc for one minute, the ceramic "Cart- wheel" is encased in a cast insulat- ing material.

C -D Midget Tubular Cornell-Dubilier has announced

production of STT Midget "Budroe" Steatite -cased paper tubular capacitors. Miniaturized versions of the company's regular "Budric" line, the new Midgets range in size from 7/32" dia. and 11/16" length to Vs"

dia. and 11/8" length. For complete information, send for Engineering Bulletin 159. Write to Cornell- Dubilier Electric Corporation, South Plainfield, N. J.

Twisted -Tab -Mounting Controls Clarostat Mfg. Co., Inc.. Dover,

N. H., announces a new low-cost mounting method for their Series 47 twisted -tab mounting controls. Material saving is accomplished by elimination bushings, mounting nuts and lock washers. Utilizing readily available tools, mounting of control is completed in one operation. Available with as illustrated) or without power switches. Controls with plastic shafts are adjustable from front or rear.

Anchor TV901 Tuner A new ,>2 -channel TV tuner de-

signed to give the customer the convenience of instant station selection, whether VHF or UHF, has just been announced by Anchor Radio Corp., 2215 S. St. Louis Ave., Chicago 23, Illinois. Channel segments (not converter strips) to suit local TV station requirements are snapped into the easily accessible turret in any desired order: they consist of simple circuits which are factory tuned and need no field adjustment.


COLOR [from page 20]

voltage at point (3) plus 2E v. This condition and intermediate phase relations are clearly shown in Fig. 7.

Notice that as the phase of the chroma signal varies with the phase of the 3.58 me reference signal, different values of R -Y signal both in amplitude and phase are developed. Needless to say, the phase of the chroma signal is directly related to the color of the chroma signal: and the amount of R -Y signal it produces is the amount of R -Y signal required to reproduce that color on the picture tube screen. Ampli- tude and polarity variations at the R -Y point for different phase angles between the chroma signal and the 3.58 lac reference signal are shown in Fig. 8.

. i Ì 360°

0 45° i

3150

! 180° 225° z i 90°135° 270° .

PHASE ANGLE

Fig. 8-Amplitude and polarity variations for different phase angles between the chroma and the 3.58 me

reference signals.

To summarize this particular section, two-phase demodulation utilizing diodes involves the addition and sub- traction of diode currents produced simultaneously by the chroma signal and the 3.58 me reference signal. The pair of diodes utilizing the in -phase reference signal comprises the R -Y demodulator, and the pair of diodes utilizing the quadrature reference signal comprises the B -Y demodulator.

High Level Triode Demodulation A basic high level demodulation cir-

cuit is shown in Fig. 9. Here, as in low level pentode demodulation, we again employ the principles of gating and sampling. Nov however we use a

Fig. 9-Basic high level demodulator circuit.

STAY AHEAD IN these SAMS books show you how

"Fundamentals of Color Television" Written by William F. Boyce. A complete explanation of Color TV written so you can understand it. Tells you all you want to know in 5 great chapters: 1. What You Need to Know About Color TV (explains principles and terms); 2. Color Picture Reproduction (describes picture tube types and function); 3. Principles of NTSC Color System (describes color signal, methods of transmission and reception); 4. Color Receivers (theory of operation); 5. Circuit Analysis of Color Receivers (full description of circuits and special components). Complete, authoritative, fully illustrated. 224 pages. 5M x 8W. Order BA -1, only.. $2.00

"Photofact Television Course" A complete, simple explanation of modern Tele- vision principles, operation and practice. Covers Cathode Beam Formation and Control; Beam Deflection Systems; Beam Modulation and Synchronization. Includes analysis of CR tube construction, camera tubes, voltage supplies, saw -tooth generators, sync circuits, control functions, receiving antenna circuits, RF input tuning systems, IF systems, AGC, etc. Fully illustrated. 208 pages, 8% x 11". Order TV -1, only $3.00

"Analyzing & Tracing TV Circuits" Milton S. Kiver's new approach to television servicing. Shows you how to best utilize the data included on the schematic, so that you can speed up repairs and earn more. Shows how to trace specific sections of a TV receiver. The importance of properly analyzing voltages on the tube elements is stressed. Helps you solve the toughest TV service problems in the short- est time. Fully illustrated. 168 pages, 8% x 11". Order JA -1, only $3.00

"TV Servicing Time -Savers" A new, extremely helpful book by Milton S. Kiver. Prepared in 5 sections presenting 51 "Time-saver Tips" showing causes and cures of common TV troubles. Shows how to improve reception; includes practical time -saving tips; covers alignment problems, etc. Any one of the 51 "tips" may save you more than the low cost of this book. 124 pages; illustrated, 5% x 8%". Order JC-1, only $1.50

"TV Service Data Handbook" A compilation by Milton S. Kiver of the most frequently needed charts, tables and formulas required in TV servicing and installation. In- cludes charts and tables on fuses, color codes, attenuator pads. A section on trouble shooting lists nearly all TV trouble symptoms along with suggestions for locating the defective component. Includes valuable mathematical constants and electrical formulas. 112 pages, 5M x 83g. Order JR -1, only $1.50

Look for the SAMS "BOOK TREE" at your Parts Distributor

Make it a habit to browse at the "Book Tree." It's loaded with the time -saving, profit -building books you want and need to keep ahead in every phase of Radio and TV servicing. Get these and other Howard W. Sams Publications at your Electronic Parts Distributor.

"Telecasting Operations" Here, in one complete, easy -to -understand volume, Harold E. Ennes tells the whole fasci- nating story of the equipment and techniques used in Telecasting. Covers such subjects as: The TV Camera; The TV Control Room; Fundamentals of Studio Lighting; Network Program Relay Systems; Maintenance Prac- tices; Technical Production; Field Equipment and Microwave Relays, plus hundreds of other subjects. 600 pages; fully illustrated; 6 x 9". Order OH -1, only $7.95

"Servicing TV in the Customer's Home" Provides practical, proved help for technicians and outside '1'V service calls. (New enlarged edition, including advance data on Color TV receivers.) Saves time, work and chassis hauling -shows how to make successful repairs on the spot by using a VTVM and capacitor probe to trace trouble; by "tube -pulling" to diagnose audio and picture trouble; by performance tests through analysis of the picture test pattern; etc. 128 pages; illustrated; 534 x 834". Order TC -1, only $1.75

"TV Servicing Short -Cuts" This helpful book describes a series of actual TV service case histories, each presenting a specific problem about a specific receiver. The symptoms of the trouble are outlined and then followed by a step-by-step explanation of how to solve it. Finally there is a discussion of how this particular trouble can be tracked down and solved in any TV set. 98 pages; 5% x 83". Order TK -1, only $1.50

"TV Test Instruments" Provides basic explanations of how each test instrument operates; describes functions of each control and shows their proper adjustment. Covers: Vacuum Tube Voltmeters, AM Signal Generators, Sweep Signal Generators, Oscillo- scopes, Video Signal Generators, Field Intensity Meters. Voltage Calibrators. Describes use in actual servicing. 180 pages; illus.; 834 x 11". Order TN -1, only $3.00

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triode. In low level pentode demodulation the reference signal is applied as a gating pulse to the suppressor grid, and the chroma signal to be sampled is applied to the control grid. In high level demodulation the reference signal is applied to the control grid of each demodulator tube, and the chroma signal to be sampled is fed into the plate circuit by transformer coupling. The resultant color -difference output signal is then applied to a 3.58 me trap where the 3.58 me reference signal component is removed. The demodulated signal however is sent on to its correct picture tube grid.

By a simple system of transformer step-up before demodulation (to be described in detail in the next installment) the correct ratios of R -Y, B -Y, and G -Y required for proper B & W color rendition are made available at the three grids of the color tube.

Coupling of each chroma signal into the plate circuit makes possible the use of high input chroma signal levels. In turn the demodulated outputs are now high enough to be applied directly to the grids of the color picture tube. This practice does away with the need for color signal amplifiers which are characteristic of low level demodulators.

In operation, a high level demodulator (taking one of the three as an example) utilizes a self biased grid so

that the tube is operated beyond cutoff on the application of the 3.58 flic reference signal. This results in a series of

sharp plate current sampling pulses much the same as in a pentode operated low level demodulator. These plate current pulses establish an average "no chroma -signal" plate voltage around which the signal driven plate voltage varies.

When a chroma signal is applied to

the plate circuit it is sampled by the 3.58 me gating pulses, and modulation takes place. A set of waveforms for an assumed chroma input signal is shown in Fig. 10. A chroma signal in phase with the sampling pulses appears as a

demodulated color difference signal in

the output of the plate circuit. How- ever, if the chroma signal is in quadrature with the reference signal, its effect on the output of the demodulator will be zero, because during plate conduction the quadrature chroma signal passes through the zero axis. This principle of quadrature signal rejection in the in -phase demodulator was discussed extensively in the previous installment.

The demodulated signal in the plate circuit contains the 3.58 me reference cw signal in addition to the chroma sig-

nal. However, this cw signal is filtered out by means of the 3.58 me trap mentioned previously. (See Fig. 9). The

48 RADIO TELEVISIONSERVICE DEALER MARCH, 1955

CHROMA INPUT

SIGNAL

DEMOD- ULATED PLATE

SIGNAL

FILTERED DEMOD-

ULATED SIGNAL

IN -PHASE DEMODULATOR

(A) (B) (C) (D)

1Ilu11 ii 1 i hii

Iillll

NO SIGNAL LEVEL\

11 -

NO SIGNAL LEVEL

r

QUADRATURE DEMODULATOR

211.11.111_

21 L f-

Fig. 10-Waveforms observed in one

of the high level demodulators. (A) represents no chroma input signal. (B) and (D) are chroma signals 180

out of phase with the 3.58 me sampling plate voltage pulse. (C) is a

chroma signal in phase with the sampling pulse.

filtered output of the demodulator is

then applied as a color -difference signal to one of the picture tube grids.

In the next installment we will dis- cuss how the correct color signal levels are obtained for proper operation of the color picture tube. This installment will describe the methods by which the correct color signal proportions are obtained in both low and high level demodulation systems.

[To Be Continued]

SQUARE -WAVE GENERATORS

[from page 25]

number of these odd harmonics were combined, the result would be a perfect square wave. In actual practice, a square wave containing only the first ten odd harmonics has sufficiently steep sides, a sufficiently flat top, and sufficiently sharp corners to make it suitable for practically any servicing problem.

Figure 5 is a simple block diagram showing a typical setup for square wave checking of an amplifier. Amplifiers are not perfect. They all exhibit several types of distortion. The better the amplifier the smaller the amount of distortion. If we could obtain a perfect amplifier, the trace on the scope would be a square wave every bit as good as the squarewave fed in by the generator. Let us suppose however, that the particular amplifier under test has a

poor low frequency response. This would mean that the low frequency components of the square wave such as the fundamental, and let us say the

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third harmonic would not be amplified as much as the higher order harmonics.

If we were now to combine the various frequency components as outlined for Figs. 2, 3, and 4, keeping in mind that the fundamental and the 3rd harmonic are not as large in amplitude as they should be (because of poor low frequency response in the amplifier), the resulting wave would have the shape shown by Fig. 6. Thus, if a wave such as that shown in Fig. 6 appears on the scope in the setup of Fig. 5, it immediately tells us that this amplifier has a poor low frequency response.

A word of caution must be injected

at this point. Suppose that the amplifier under discussion cuts off rather sharply all frequencies below 200 cps. If the frequency of the square wave input to the amplifier is 60 cps, then naturally it will contain a 60 cps component and a 180 cps component, both of which will be severely attenuated and therefore give rise to the distorted square wave output shown in Fig. 6. Suppose now, however, that a 1000 cps square wave is fed into the input of the amplifier instead of the 60 cps. In this case the lowest frequency component being fed into the amplifier would be the 1000 cps fundamental. All the


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other harmonic components would h, higher in frequency. In this case (assuming that the high frequency response is good, and that there is negli- gible phase distortion) the trace on the scope would indicate a good square wave output IN SPITE OF THE FACT THAT THE AMPLIFIER HAS A POOR LOW FREQUENCY RESPONSE. This of course is very misleading. The technician therefore must be sure to select square wave frequency which will include harmonics within the range being tested. This leads to a system of two and three point testing which will be discussed in the next installment.

[To be continued]

ANSWERMAN [from page 28]

placing the picture tube in a face down position and lightly tapping the neck and base of the tube. It may be possible to perform this operation with the picture tube in the cabinet if normal caution is observed concerning pressure on the controls on the front of the cabinet. It is usually advisable to place some soft material on the floor before turning the cabinet over.

2. If the above procedure does not alleviate the arcing or shorted condition it may be desirable to attempt to burn loose the particles before replacing the picture tube as defective. First, of course, determine between which elements the particles are located. This can usually be done with an ohmmeter. Then ground one of the shorted element socket pins with a jumper and connect a positive voltage to the other element pin. This operation is best performed with the picture tube in a face -down position. The application of the voltage, possibly boost B plus, usually will cause sufficient current to flow to burn open the shorting particles. It is to be hoped that at the same time the electrode connections are not burned open first, however.

*See Jan. RTSD, pages 14 and 24.

WORKBENCH [from page 261

100K instead of 1 meg. When R415 was replaced the receiver functioned properly.

In order to understand why a vertical fold -over occurs when R415 drops in resistance to 100K let us refer to the diagram. The RC time (T=RC) of C408, .1 »f and R415, 1 meg is large enough to pass the incoming ver -

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tical saw -tooth without any distortion. However, when R415 drops to 100K, the RC time is now 1/10 its previous value. C408 will now be able to charge up so quickly that during the remainder of the incoming saw -tooth time, it cannot charge much more so that appears flat topped as in Fig. 1B. Depending on the vertical linearity and size adjustments, grid current could be drawn causing an even greater flattening effect, which on the raster appears as a

fold over on the bottom. Naturally, the smaller R415 gets, the greater will

be the fold over at the bottom of the raster.

Emerson 734 B, Chassis 120169-B The receiver was turned on and the

vertical hold was adjusted properly. After about ü hour the vertical frequency started to drift out of range. Because this was a vertical frequency problem, the vertical oscillator V18, 6SN7, was replaced but had no effect.

The diagram was then studied and it was observed that the receiver uses a cathode coupled vertical multi -vi -

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A DIVISION OF GLOBE -UNION INC. 914C E. Keefe Avenue Milwaukee 1, Wisconsin

STATEMENT REQUIRED BY THE ACT OF AUGUST 24, 1912, AS AMENDED BY THE ACTS OF MARCH 3, 1933, AND JULY 2, 1946 (Title 39 United States Code, Section 233) SHOWING THE OWNERSHIP, MANAGEMENT, AND CIRCULATION OF RADIO -TELE- VISION SERVICE DEALER, published monthly at New York, N. Y. for October 1, 1954.

1. The names and addresses of the publisher, editor and business managers are: Pub- lisher, Sanford R. Cowan, 6 Embassy Court, Great Neck, N. Y. Editor, Sanford R. Cowan, 6 Embassy Court, Great Neck, N. Y.; Managing Editor, Samuel L. Marshall, 262 Sullivan Place, Brooklyn, N. Y.; Business Manager, Sanford R. Cowan, 6 Embassy Court, Great Neck, N. Y.

2. The owner is: (if owned by a corporation, its name and address must be stated and also immediately thereunder the names and addresses of stockholders owning or holding 1 per cent or more of total amount of stock. If not owned by a corporation, the names and addresses of the individual owners must be given. If owned by a partnership or other unin- corporated firm, its name and address, as well as that of each individual member, must be given.) COWAN PUBLISHING CORP., 67 West 94th Street, New York 36, N. Y.; Sanford R. Cowan, 6 Embassy Court, Great Neck, N. Y.

3. The known bondholders, mortgagees, and other security holders owning or holding 1 per cent or more of total amount of bonds, mortgages, or other securities are: None.

4. Paragraphs 2 and 3 include, in cases where the stockholder or security holder appears upon the books of the company as trustee or in any other fiduciary relation, the name of the person or corporation for whom such trustee is acting; also the statements in the two paragraphs show the affiant's full knowledge and beliefs as to the circumstances and conditions under which stockholders and security holders who do not appear upon the books of the company as trustees, hold stock and securities in a capacity other than that of a bona fide owner.

(Signed) S. R. COWAN, Publisher Sworn to and subscribed before me, this 20th day of August, 1954.

HARRY N. REIZES, Notary Public

brator as an oscillator. Most receivers use the blocking oscillator type to gen- erate the vertical sweep voltage. In V18 feed back occurs across the common cathode. The vertical hold control, R90, 1 meg, controls the free run- ning frequency. In this multi -vibrator all the components in the circuit will effect frequency to some degree. How- ever, the components that affect frequency most are C66, .0047 uf, R91, 820K, and R90 the 1 meg vertical hold control.

C66 was voltage leakage checked and found to be okay. R91 was then measured and its resistance also checked correctly. However, when 1190 was measured, instead of reading 1 meg at maximum, it only measured about 700K. The vertical hold control was then clipped out and measured again. It now measured properly at 1 meg. It was concluded therefore, that some parallel resistance was taking effect.

The circuit was then traced out and it was discovered that R91 and R90 were connected at Pin #1 (unused pin) of the 6W6, vertical output tube. R91, 820K was next clipped from pin el and a resistance measurement was taken from pin el of the 6W6 to ground. To our amazement even though this was an unused pin with nothing connected to it at this time, the meter read 2 megs. The 6W6 tube was next pulled out of the socket and the meter now read infinite. On further examina- tion of the 6W6 tube a leakage of 2 megs was discovered from pin el, unused, to the filaments pins e2 and 7. R91 and R90 were next soldered directly together, eliminating the use of pin #1 as a tie póint, and a new 6W6 was put in. The receiver was checked for two days and showed no sign of vertical frequency drift.

P.A. ROUNDUP [from page 13]

the installation high? Where the answer is "ves," medium or high -power directional -type speakers are called for.

5. When a long narrow area (such as a school corridor) is to be covered, bi-directional speakers are economical.

6. If the speaker is to be used in an atmosphere of extreme humidity, excessive dust, or chemical pollution, a sealed -in or "submergence -proof" speaker is a must.

7. In locations where a spark from the speaker mechanism could cause an explosion, explosion -proof speakers are called for.

8. When wide-angle coverage is desired, radial -type speakers with a 360-


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degree sound distribution pattern are economical.

Matching Speakers to Amplifiers For distortionless, efficient operation,

speakers must be matched to the output impedance of the amplifier used. When more than one speaker is employed, series of parallel connection of the units is possible. Parallel connection is generally preferred, in part because failure of one speaker will not render the others inoperative.

To determine the impedance of speakers in parallel, divide the impedance of one speaker by the number of speakers used (it is assumed that all the speakers have the same impedance). In the case of series -connected speakers, the net impedance is equal to the sum of the individual speaker impe- dances.

Speakers should be connected so

that they move in phase -with each other. Proper connection of identical speakers is indicated in Fig. 7.

Location of Speakers Speakers should be so located that

the space between the speaker and its area of coverage is free of obstructions. The speaker should be beamed toward the center of the area covered.

When a speaker and a microphone must be set up in the same vicinity, they should be positioned in such a

way that a minimum of direct or re- flected sound will be returned to the mike, otherwise feedback will result.

Speakers should be oriented so that sound is kept off the ceiling and side walls, which are highly reflective, and concentrated instead on areas where people will he seated.

Speaker Housings The choice of an enclosure for a

speaker is an important part of an indoor pa installation. Some of the factors to be considered in the choice of an enclosure are:

1-Location where enclosure is to be used.

2-Frequency response desired in system.

3-Angle of coverage. 4-Method of mounting. 5-Cost. In the case of installations in

churches, auditoriums, and similar sites, reverberation is often a problem. Re- verberation produces a loss in intelli- gibility, and must therefore be min- imized. Reverberation of low frequencies is more of a problem than high - frequency reverberation, because the time of reverberation is longer. Cer- tain types of compact housings will, by attenuating the low -frequency response, reduce low -frequency reverberation.

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Fig. 7-Properly phased connection of speakers in parallel (left); in series (right). (Courtesy Newcomb Audio Products Co.)

Some housings serve as two-way speaker enclosures; because of their design, sound coverage from both the front and rear of the speaker is per- mitted. This is advantageous in long, narrow areas.

Different degrees of tilt are available in different enclosures, permitting downward beaming of the speaker at the angle best suited to maximum coverage of the area.

Overload Protection of Speakers Speakers are apt to break down un-

der temporary overload, rendering the pa system at least partly inoperative. One of the methods of preventing such inconvenient and costly breakdowns is

described below. "Grasshopper fuses"-the kind com-

monly used by the telephone company -are employed to protect the driver unit of each speaker.

Fuses rated at approximately 1 amp. are generally employed, in the case of

speakers using less than 25 watts of power. When a 25 -watt driver with a 16 -ohm voice coil impedance is used, a fuse with a rating of P/ watts (but not larger) is recommended. The fuses described are inexpensive, and may be obtained from the Gravbar Electric Co. Blowing of a fuse causes a contact arm to be released, removing the voice coil from the circuit and causing a l5 -ohm resistor to be substituted in its place.

Microphone Considerations An important consideration that is

often overlooked in the choice of a mike is the cable length that will be used with it. If a cable 25 feet or longer is to be employed, and high -frequency reproduction is demanded of the system, a high -impedance mike should not be employed, because the long line required will reduce the frequency response of the system. A low -impedance mike is preferable in such a case, because a long line will not seriously

Fig. 8-Altec-Lansing "Lipstik" miniature microphone.

affect its response. The greater ruggedness of the cables used with low -impedance microphones makes it preferable to use this microphone type in cases where the cable associated with it will be subjected to considerable abuse (as in a night club installation, for example).

Important characteristics of a mike are: frequency response; power output; sensitivity; directional characteristics; output impedance; hum pickup; and cost. Physical characteristics such

NON-MAGNETIC STAINLESS STEEL TIP & LUCITE BODY

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* Short alignment tool for No. 6 to 8 slug -tuned coils like those under picture tubes.

* Designed to fit popular tube carrying cases.

* Non -Magnetic stainless steel tips assure no detuning of circuits and long wear.

Send Checks or Money Orders Only No C.O.D. Orders Accepted.

TELE-SCOPIC PRODUCTS, INC. 215 W. 33rd St. New York 1, N. Y.

BUY DIRECT Manufacturer to Dealer

ANTENNAS INSTALLATION Hardware and

Accessories WRITE FOR CATALOG

et, Ì R (_'.

94' P.O. BOX 68B McHENRY, ILL.

MOVING? Please Mail Us Your Change of Address Also be sure to include your old address, and code line from the mailing label. Or, if you prefer, tear off the entire label and send it along with your new address. Duplicate copies cannot be sent.

RADIO -TELEVISION SERVICE DEALER

67 W. 44 Street, New York 36, N. Y.


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as size, weight and ruggedness must also be considered in many applications.

An interesting member of the microphone family is Altec-Lansing's "Lip- stik" mike (Fig. 8) said to be the small- est microphone on the market. The mike uses a sub -miniature tube in a hase that is highly shock -resistant. A printed circuit is employed between tube socket and microphone cord, min- imizing the space needed for wiring. Mike and base are 31/2 inches long and 0.6 inches in diameter. The unit is intended for applications where microphone concealment and unimpeded nobility of the performer are desirable.

Microphone Stand Development An interesting development in mi-

crophone stands is a "Safety Air Lock Cushion" used in a boom stand being put Out by the Atlas Sound Corp. (sec Fig 9). The mechanism prevents any sudden accidental slipping of the tele.

Fig. 9-(Left) Mike stand by Atlas Sound Corp. The mike stand on the

right is by Snyder Mfg. Co.

scoping section. Such slipping can, in the case of other types of stand, cause a blast of sound to come from the amplifier. to say nothing of the possible damage it can cause the microphone. If the clutch -holding adjustment is in- sufficiently tightened or accidentally released, the resultant controlled es- capement of air permits only a slow, smooth and quiet collapse of the stand.

Another mike stand with a collap- sible base is shown in Fig. 9. This item is manufactured by Snyder Mfg. Co. of Philadelphia and goes under the model No. MS -2.

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Advertising Index

Aerovox Corporation 16

Alliance Manufacturing Co. 14

American Microphone Co.. 6

American Television & Radio Co 56

Atlas Sound Corp. 56

B & K Manufacturing Co 49

Bussmann Manufacturing Co 18

Cadillac Trading 44

Centre lab 43, 52

Chicago Standard Transformer Corp.....22

Columbia Wire & Supply Co 44

Delco Radio, Div. of General Motors Corp 7

Hycon Manufacturing Co 13

International Resistance Co. Cover 2

Jensen Industries 56

Jersey Specialty Co 48

Littelfuse, Inc. IO

Mosley Electronics 48

National Radio Institute 51

Oelrich Publications 55

Oxford Electric Corp. . . . 42

Phaostron Company 33

Philco Corporation 8, 9

Pyramid Electric Co 21

Radiart Corporation 17

Raytheon Manufacturing Co 2

RCA Tube Dept Cover 4

Rider, John F., Publisher 55

Sams, Howard W., & Co 47

Skysweeper, Inc. 54

Snyder Manufacturing Co Sonotone Corporation 45

Standard Coil Products Co., Inc...Cover 3

Superei Electronics Corp 51

Technical Appliance Corp 5

Tele-Scopic Products, Inc 54

Transvision, Inc. 44 Triad Transformer Corp 53

United Catalog Publishers 48, 56

University Loudspeakers 53

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In Canada: Atlas Radio Corp., Ltd., Toronto, Ont.


Editorially approved by HOWARD SAMS Photofact Reporter* --

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Buy the set owners' goodwill and loyalty by selling them "invisible" conversion with Standard Coil UHF strips in

their Standard Coil tuner.

Strip conversion is "designed in" conversion developed by the same engineers who designed the tuners used in

the sets. And-no extra box, no extra wires, no extra tuning knobs-and the absolute minimum of interference.

And Standard Coil "invisible" conversion is simple to install and easy to align. Capitalize on the steady demand for UHF

conversion. This is all that's needed for each channel converted (actual size).

*Vol. 3, Vo. 2-page 35 and following

COIL PRODUCTS CO., INC. CHIICAGO LOS ANGELES BANGOR, MICH. NO. DIGHTON,MASS.

Export Agent: Rocke International Corporation, 13 E. 40th Street, New York City

GET READY FOR ... NATIONAL TELEVISION

SERVICEMEN'S WEEK

MARCH 7-12

Television dealers and service tectin.cii_ns all over :he cour_t_r are preparing to tie-in with a great promotional event. It's Natic.nal Television Servicemen's Week, parch 7-12. sponsored by t1 -e RCA Tube Division and registered officia:ly wit :he Chamber of Coaamerc= of the United States.

You can use this unique mercit.ncisiag plan right in your cwn neighborhood to meet and sell more telezision service prospects tan ever before. Your RCATube Distrbu:ar ofer s you excellent prompt: anal materials to help you idetuifì yourself and your store with this nationwide consumer Promotion.

Plan an active Participation in National Television Servicemen's Week now. Act ID -day! See your RCA Tut e. Distributor for full details_

RADIO CORPORATION Of AMERICA J ELECTION TLB!S NARR/SON, N.J.

Use These Promotional Materials

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