june - americanradiohistory.com...trons, called valence electrons, may be torn away from the atom by...

JUNE1957

5o

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4. Card Reader5. Cardatron Input6. CardatrOn Cort-ol7. Cardatron Output

8. Printer

9. FlexowrIter

10. Tape Controll-n.t

Power Amplifiers in Hi Fi

Marine Radio Direction Finders

Transistor Theory

Vertical Retrace Blanking

Taxicab Communications Systems

AR -22

TR-4

TR 11 and 12 14

AR 1 and 2

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EDITORIAL STAFF

Sanford R. Cowan Publisher

Samuel L. Marshall Editor

Oscar Fisch Associate Editor

Robert T. Dargan Technical Editor

David Fish Editorial Assistant

Irving Tepper Editorial Assistant

Charles W. Gardner, Jr. Production Manager

San D'Arcy Contributing Editor

Paul Goldberg Contributing Editor

Elbert Robberson Marine Communications Editor

Lawrence Fielding Hi-lri & PA Editor

BUSINESS STAFFAdvertising Sales

New YorkandEast

Chicagoand

Midwest

WestCoast

Richard A. CowanJack N. Schneider300 West 43rd StreetNew York 36, N. Y.JUdson 2-4460

Jim Summers

Suite 55 CPure Oil Building35 E. Wacker DriveChicago 1, III.

ANdover 3-1154

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David Saltman Business Mgr.

CIRCULATION

Harold Weisner Circulation Manager

Carol J. Binderman Ass't Circulation Mgr.

Madeleine Sturmer Circulation Processing

ELECTRONIC SERVICING ( formerly Radio -TV ServiceDealer) is published monthly by Cowan Publishing Corp.,300 West 43rd Street, New York 36, New York, JUdson2-4460. Subscription Price: $3.00 one year, $5.00 two yearsin the United States, U. S. Possessions, Canada and Mexico.Elsewhere $1.00 per year additional. Single copies 50c. Sec-ond Class Mail privileges authorized at New York, N. Y.

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VOL. 18, NO. 6 Member

SPA

FEATURE ARTICLES

JUNE, 1957

Introduction To Transistor Theory, by George BrowneDescription of semiconductor action simplified

Radio Direction Finders In Marine Electronics, Part 2, by Elbert Robberson

Preliminary precautions to be observed when installing direction finders.

Vertical Retrace Blanking, by Irving TepperTechniques for adding and servicing vertical retrace circuits.

Radio Performance and Noise Suppression in Taxicab CommunicationSystems, by George A. Svitek

Valuable techniques to ensure satisfactory system operation.

TV Cooking Bench, by Harry J. MillerAn ounce of prevention is worth a lot of callbacks.

Power Amplifiers In Hi Fi, by Lawrence FieldingCalculation of power requirements for various room sizes.

CIRCUIT AND SERVICE FORUM

2

4

6

8

12

16

Complete Manufacturer's Schematics-TV17-32

Admiral 19Z4RS. 19Z4PRS RCA KCS 101 Ch.

G.E. ST line Zenith Ch. 1530

Video Speed Servicing SystemsEmerson Ch. 120292 P, VMuntz Ch. 49A4

Workbench

33-36

Answerman

DEPARTMENTS

Trade Flashes

Association News 38 Rider Speaks 41

Advertisers' Index Cover III

37

42

16 Trade Literature 40

THIS MONTH'S FRONT COVER

Artist's rendering of Datatron system featuring idealplacement of component parts. Electronic automation ofoffice operations offers tremendous opportunities for theenterprising electronic serviceman. ElectroData, Pasadena,California.

Entire Contents, Copyright 7957, Cowan Publishing Corp.

COWAN PUBLISHING CORP., 300 West 43rd Street, New York 36, N.Y.

ELECTRONIC SERVICING JUNE, 1957

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Introduction to Transistor Theoryby George Browne

A down-to-earth presentation of the essentials oftransistor theory for the serviceman with an eyeto the immediate present and the imminent future.

UNDERSTANDING transistorsrequires an understanding of

semiconductors and their characteristics.A semiconductor is a material with aconductivity less than that of a con-ductor and greater than that of an in-sulator.

The degree of conduction in anymaterial depends largely on the num-ber of free electrons present. In a con-ductor this number is large. In a semi-conductor it is small. In an insulatorit is insignificant.

The number of free electrons presentin a semiconductor depends on suchfactors as: heat, light, the applicationof external magnetic and electric fields,and the presence of impurities withinthe semiconductor.

Of particular importance in transis-tors is the manner in which such im-purities produce free negative, or equiv-alent positive, charges within the semi-conductor. To understand this action itbecomes necessary to understand thestructure of the atom itself.

To this end we direct our attentionto Fig. 1 which illustrates a simplifieddiagram of an atom of germaniumwhich is the most commonly usedmetal employed in transistors. In thissimplification we show a core whichcontains the inner ring electrons as wellas the neutrons and protons that makeup the nucleus of the atom. We alsoshow an outer ring of electrons, the lat-

.0 Fig. 4-Production of holes.

ter being four in number. These elec-trons, called valence electrons, may betorn away from the atom by the appli-cation of suitable forces. As such theybecome free electrons.

In Fig. 2 we observe how the manyatoms contained in a sample of germa-nium may be pictured as being con-nected to one another. Here we see acore of atom "A" (black) surroundedby its four (black) valence electrons.Also surrounding the core are four ad-jacent atoms, each marked with an X.Although only atom B of this group isshown with its four valence electrons(these being identified by small X's)all of the other atoms are also sur-rounded by four valence electrons asexplained in the previous paragraph.

Focusing our attention on a singlepair of these electrons such as 1 and 2,1 being associated with the core of atomA, and 2 with that of atom B we ar-rive at certain conclusions with regardto the mutual forces being exerted.First, atom B exerts a force of attrac-tion on electron 1, while atom A exertsan equal force of attraction on electron2. Thus, electrons 1 and 2 act as theconnecting links that serve to keepatom A bound to atom B as shown inthe figure. It must be understood thatcore A also exerts a force of attractionon electron 1, so that electron 1 is ac-tually shared by atom A and atom B.A similar condition obtains for electron2. This same arrangement extends toother atoms one of which is shown inthe upper right. Electrons 1 and 2 and

their counter -parts throughout the crys-tal structure form what are commonlyreferred to as "electron bonds," the lat-ter being in effect types of dynamiclinkages between atoms which tend tomaintain the entire structure intact.This structure is called a lattice.

Electron Shells

Studies in chemistry and physics re-veal that atoms are stable when the out-er or valence ring contains eight elec-trons. In fact, there is a strong tendencyfor atoms whose outer rings containless than eight electrons, to acquire asufficient number of electrons, fromwhatever source may be available, soas to enable these outer rings to con-tain eight electrons. As a matter of factthe tendency to complete such a ringmay be so great that in many cases itovercomes the attractive force of a

neighboring core on one of its own out-er electrons, and "steals" this electron.

Of particular interest is the case pre-viously discussed, and illustrated in Fig.2, where electrons of adjacent atomsare "shared" rather than stolen. Thuselectrons 1 and 2 in the figure areshared by atoms A and B.

"N" Type Germanium

If an impurity atom of some othermaterial such as arsenic is added togermanium, which has a lattice struc-ture corresponding to Fig. 2, it will ac-tually displace one of the germanium

2 ELECTRONIC SERVICING JUNE, 1957

atoms, becoming part of the structurein the manner shown in Fig. 3. Arsenic,having five outer ring electrons, forms astable structure of four valence bondswith the germanium electrons as

shown, resulting in one superfluouselectron. The end result is the produc-tion of a free electron and a single un-balanced positive charge in the arsenicnucleus. This is a stable condition, be-cause by sharing electrons the outerring of each atom contains eight elec-trons.

Impurity atoms, such as arsenicwhich result in the production of freeelectrons (negative charges) in a semi-conductor material such as germaniumare called "donors." Germanium, toWhich arsenic (or any other suitablepentavalent material) is added in con-trolled amounts is referred to as N -typegermanium. it must be kept in mindthat the actual ratio of impurity atomsto germanium atoms in a typical pre-pared sample is very small, approxi-mately 1 in 10 million. Some other im-purity elements which may be used toproduce N type germanium are anti-mony and phosphorus.

The addition of an impurity atomcontaining three electrons (trivalent)such as indium, gallium, boron, or alu-minum, produces different results.Now, as shown in Fig. 4, the threevalence electrons of indium enter intovalence bonds with three of the fourgermanium valence electrons. Noticethat the germanium atoms B, (see Fig.2.) previously linked to the displacedatom A, is left with one of its valenceelectrons unshared. A vacancy thereforeoccurs in the outer ring, which nowcontains only seven electrons. The spacewhich lacks an electron to complete thefinal valence bond is called a "hole."

The tendency to establish an 8 -elec-tron ring shell in this case is strongerthan the energy binding one of thevalence electrons to a neighboring ger-manium atom such as C. As a resultthis electron is robbed from the outerring of atom C. The 8 -electron shellstructure between the indium atom andits four surrounding germanium atomsis now complete.

Inasmuch as the process involves at-traction or gaining an outside electron,

[Continued on page 44]

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Interconnecting wiring must be routedaway from disturbing elements.

THE previous installment discussedthe directional characteristics of

various types of antennas which areused in radio direction finding. Thisinstallment deals with practical loop de-sign, and discusses the problems in-volved in installing the equipmentaboard ship.

Commercial vs. SmallCraft Installations

The first radio -direction -finder instal-lation I worked on was a commercialjob. It took a couple of men severaltrips to carry the equipment aboard,and a couple of days work to get it inplace, connected up, and operating.After that the direction finder was cali-brated, a project involving three tech-nicians, a special transmitter in a rentedpowerboat, and taking the ship out toa clear spot in the harbor.

This procedure was by no meansunique. Professional installers of equip-ment on commercial vessels still con-sider a radio -direction -finder installation

Direction Finders In Marine ElectronicsPart 2

Part 2 of this 3 -part article deals with theprecautions to be observed in the preliminarystages of installing marine direction finders.

an extensive project, requiring closework between electricians, ship fitters,engineers, and the navigating personnelof the ship.

But things are much different in thesmall -boat field. Today, the purchaserof many a marine direction finder tucksit under his arm, carries it aboard, placesit on a table somewhere, and considershimself "in business." True enough, theequipment will pick up the various bea-cons and broadcast stations, and nullsare obtainable. Mere possession of a ra-dio direction finder, however, does notwrap an electronic coat around the ves-sel to protect it from the chill of fog.The fact is that the commercial instal-lers do not go to all of the trouble theydo simply to pad the bill. Careful in-stallation of a radio direction finder isabsolutely required for any degree ofreliability, and in many cases, calibra-tion of the equipment is essential ifbearings are to be trustworthy.

Although vendors of the modernsmall radio direction finders do notstress the point, this equipment is asvulnerable to bearing inaccuracy, be-cause of the rigging and top hamperof the vessel in which they are installed,as are the large steamship types ofequipment. Bearing accuracy with eitherkind of equipment may slide many de-grees off in one sector or another, andthe inaccuracy may change from fre-quency to frequency. For this reason, aradio -direction -finder installation shouldnot be considered as completed until theinstaller has checked the operation of

the equipment and furnished a calibra-tion curve or chart as necessary, or elseinstructed the skipper of the boat onhow he may perform this importanttask himself.

Location of the Direction finder

But to get back to the installation,the choice of a proper location for aradio direction finder is very important.It is not enough to find clear space ona shelf or table, and then simply screwthe cabinet in place. For accurate andsatisfactory direction finding, the loca-tion for the equipment must be chosenvery carefully. This is not the place forcursory inspections and snap decisions.Before choosing the location, the entireenvironment of the spot should be stud-ied. Things to avoid are metallicmasses, electrical conductors, riggingwires, stove pipes, etc., close to the fieldof the loop. Sources of possible radionoise, and large moving objects are alsoto be avoided. Many boats have metalwindow screening which may have anundesirable effect on a loop receiverplaced immediately alongside.

Another thing to watch for is thepresence of metal conduit, wiring, orpiping, concealed inside wooden mem-bers of the cabin or wheel house inwhich the equipment is being installed.Without checking the top and bottomof such a wooden member, the installermight place the equipment in a posi-tion where the direction -finder loop wasdirectly alongside a mahogany post that

actually concealed a copper ventilatingduct for the engine room. It is neces-sary to check the structure and wiringplan of the area in which the directionfinder will be installed, and then toplace the equipment as far as possiblefrom the disturbing elements.

Using the Ship's Power Supply

Many modern radio direction findersare of the portable type with self-con-tained batteries. However, the largerand more professional type of equip-ment is powered by a vibrator powersupply, or dynamotor, from the ship'smain or auxiliary batteries. Direction -finder power consumption is compara-tively small, running in the neighbor-hood of from three to six amperes at6 volts, to one or two amperes at 32volts. Nevertheless, the equipment or-dinarily should not be tapped into anyother existing power line. Although anexisting line may have sufficiently largeconductors to carry the current, its rout-ing through the vessel and the connec-tions which are made to it, may bedisadvantageous to best direction -finderoperation because of the possible pick-up of extraneous noise and signals.

Well engineered vessels will probablyhave extra terminals on their switch-boards for such equipment as the radiodirection finder. In this event, connec-tion is made to the board. Otherwise,an extra fused terminal should beadded to the switchboard.

To reduce unwanted noise and signal


by Ellbert Robberson

pickup in the power line, it is bestto install direction -finder wiring ingrounded metallic conduit or else toemploy shielded cable. Although powercircuit by-passing is employed in direc-tion -finder receivers, it is still a goodidea to keep such "back -door" noiseand signal levels to as low a value aspossible. To help this power line filter-ing, it is also desirable to ground theequipment cabinet to the radio groundby a short and direct lead.

Some equipment has a power supplyexternal to the cabinet. If at all pos-sible, this should be placed some dis-tance below the receiver -and -loop as-

sembly in order that noise pickup fromthe vibrator or dynamotor be mini-mized. Another caution is to alwaysmake certain that the ground polarityof the equipment power supply is thesame as that of the boat's 'battery sys-tem. I have more than once, receiveda jolt - mental as well as physical -from several hot -and -healthy volt's dif-ference of potential between equipmentpower supplies and nearby groundedobjects. The negative side of a circuit isnormally grounded. In marine batterysystems, however, the positive side isvery often grounded, so 'watch out forthis peculiarity and check the groundpolarity of the battery system beforeturning power on the equipment youinstall. Equipment may be made to con-form to the boat -battery ground polarityby reversing the vibrator, or changingthe connection of a couple of internalleads supplied for this purpose.

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ELECTRONIC SERVICING JUNE, 1957 5

v111

6K6

C156.001

T108VERT. OUTPUT

R202 --560

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lt

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V11 A

1/212BH7VERT. OSC.

TO VERT.OUTPUT

W1 C62

717\ .05

C157 W2.;7" R53

0 HEIGHT R52

CONTROL 3300

TO CRT 5 MEG. TO CRT

CATHODE WITH '1'. GRID

C158

1 MEG.

STOP R511800

Fig. 1-Pulse applied to cathodeof CRT via capacitive divider.

W3

B+

T106C133.005

C134.047

/ITR1445.6K

I V110A

1/2126H7VERT OSC.

TO GRID OFVERT OUTPUT

R14641 MEG.

TO BOOSTB+

C136.0005

TO GRIDOF CRT

R145820 K

TO PLATEOF V402

6S4VERTOUT.

r

B+

C427.01

R4452700 of

I '

c428

,r12

I

63C6-1256K

I

COUPLATE----ri R444TO

CONTROLGRID

OF CRT

Fig. 2A,B,C-Methods used to obtain blanking pulses for th a CRT grid. At A, (left) the pulse is obtained from the peak-ing resistor in the trapezoidal forming circuit; at B and C, (center and right), the trapezoid is differentiated.

Vertical Retrace Blanking

by Irving Tepper

ERY often a serviceman encoun-ters a receiver that has a bad case

of "retrace lines." The lines cannot beeliminated without loss of good pic-ture brightness. To overcome this defect,many modern television sets incorpo-rate sweep blanking circuits. The serv-iceman's outlook is two -fold. He mayhave to service these blanking circuitsor he may find it necessary to add ablanking circuit to a receiver not al-ready having one.

Need For Blanking Circuits.

It might be asked why a blankingcircuit is necessary if blanking pulsesare transmitted as a part of the com-posite video signal. The need for ad-ditional blanking may be better under-stood from the following discussion.

The appearance of vertical retracelines is caused by insufficient blankingvoltage at the driven element of theCRT during the retrace period. Thiscondition may be a result of any oneof several causes, the simplest being amisadjusted brightness control. Correc-

tion of the CRT bias with the bright-ness control will restore normal opera-tion. There are situations howeverwhere the brightness control does notcompensate properly. These may be:

I. A weak CRT2. Extreme program material3. Poor circuit design4. Loss of gain in the video strip

With a weak picture tube, it becomesnecessary to lower the bias in order toachieve acceptable brightness. This shiftof the operating point towards zeroprevents the blanking pulse from ex-tending into the cut-off region, thusmaking the retrace lines visible.

Extreme program material may alsobe a factor since very dark scenes fre-quently show retrace lines. The dc re-storer should develop a correcting biasbut it is often unable to produce suf-ficient restoring voltage for very darkscenes.

Sets using direct coupling betweenthe last video amplifier and the CRTexhibit a marked tendency to show re-trace lines. If the picture tube emissiondrops the situation worsens consider-ably.

The addition of vertical retrace blanking cir-cuits and the problems encountered in the ser-vicing of these circuits are treated in this article.

Retrace Blanking Circuits.

The simplest corrective measure is amodification of the set to accept a ver-tical blanking circuit. This circuit willperform the blanking duty during thevertical retrace period. The amplitudeof the blanking pulse is so great, from40 v to 70 v peak to peak, that no retracelines can possibly show. Even betweenchannels with no video signal presentand maximum brightness, retrace lineswill not appear. The simplicity of theblanking circuit is such that a majorityof manufacturers now include it asstandard circuitry.

The circuit operation is extremelysimple. A pulse is taken from the ver-tical circuit, shaped, attenuated and ap-plied to an element of the CRT whichcan control the beam intensity.

When the video signal is applied tothe control grid of the CRT, the blank-ing pulse is fed to the cathode. In Fig.1 the blanking pulse is taken from thehigh side of the vertical deflection coil,attenuated by the action of capacitorsC157 and C158. It is then applied as apositive pulse to the cathode of the

CRT, driving the pix tube into cut-offduring retrace. A variation of this cir-cuit is shown in Fig. 6B.

Since many receivers apply the videosignal to the cathode of the CRT, theblanking pulse is fed to control grid.This requires that the blanking pulsebe negative. Three such circuits areshown in Fig. 2. In Fig. 2A the sourceof the blanking pulse is the trapezoidforming circuit in the output of thevertical oscillator. Resistors R51 andR52 develop negative pulses, W2 andW3 in the figure, which are added tothe sawtooth developed across capacitorby C62 to form a trapezoidal wave,W4. The pulse across R51 is negative,and occurs during retrace time. Thus itis suitable for application to the controlgrid of the CRT. The circuit of Fig.2B also applies a negative pulse to thecontrol grid by differentiating the tra-pezoidal output of V110B through ca-pacitor C136 and resistor R145. In Fig.2C the trapezoid is taken from thelower side of the vertical deflectioncoil, differentiated, and applied to thecontrol grid of the CRT. Compare thiscircuit to that shown in Fig. 1 and note


R3180319

47 K

TO PLATE.01

OF VERT.OUTPUT

V9 ----1/212SN7

R3161 MEG.

TO 1st. ANODEOF CRT

C37910

R320100 K

R3783.3 K

TO BOOST B+

Fig. 3 -1st anode blanking used insome General Electric models.

that in order to change the polarity ofthe pulse, it was necessary to reversethe B plus feed and the pulse take offpoint. The circled polarities in Figs. 1and 2C are the instantaneous polaritiesduring retrace time.

First Anode Blanking.

Blanking may also be accomplishedat the first anode of the CRT as is donein some GE receivers. The circuit,shown in Fig. 3 is not used frequentlysince it requires the use of a triode(V9) exclusively for blanking. V9 isgrid leak biased and is in cut off duringthe vertical trace. Since no plate cur-rent flows in V9 the voltage drop acrossresistors R320 and R378 is due to thefirst anode current. When vertical re-trace occurs, a positive pulse is appliedto the control grid of V9 through C311and R318. This pulse drives the gridpositive, brings V9 out of cut off, andrecharges C311. The heavy conductionof V9 creates a large voltage drop acrossresistors R32() and R378 and lowers thefirst anode voltage to a point where theCRT is cut off.

Service Problems.

Due to the simplicity of most blank-ing circuits few service problems arise.Those that do, usually affect the rasterso that we have maximum brightnesswith no control or no raster at all. Thecircuit shown in Fig. I can developeither difficulty. Should C157 short, the


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7458

Radio Performance and

in TAXICAB

Reproduction permission granted by G.E. Original article appeared in TAXICAB INDUSTRY, April, 1957.

AMODERN FM set is an intricate andprecise tool. Under favorable con-

ditions it can detect and translate intofully audible information a signal onlyhalf of one millionth of a volt. Thinkof it! By comparison, normal ac linevoltages found in a home are over twohundred million times stronger.

The FM receiver is designed to ac-cept all electrical signals which fallwithin its frequency band. It has noway of determining whether the elec-trical signal is a desired or an undesiredsignal. Therefore, the receiver will dowhat it was designed to do: It will de-tect any intelligence on signals fallingwithin its pass band, regardless of theorigin of those signals.

By way of analogy, most taxi com-panies are familiar, we believe, withchannel -sharing which becomes neces-sary due, to the large number of radiousers in a small frequency spectrum.When one transmitter is on the air, theothers must stand by and wait until themessage is concluded. As a means ofexplaining electrical interference, let usthink of noise sources on a cab as smalltransmitters, some powerful and someweak, sending out signals on the re-ceiver frequency and trying to hog thechannel. Since these small transmittersare on continuously, the only hope ofgetting effective channel utilization isto silence or weaken as many of thesesources as possible.

Noise Sources-What Are They?In taxis, the most prominent noise

source is the ignition system. There areat least five points within the ignitionsystem which can generate noise, and

which merit consideration. The mostobvious source is the spark plug itself.The distributor gap is another source ofnoise. The breaker points located in thedistributor are a third source. Looseconnections within the ignition wiringare a fourth possible source, and thecoil is the fifth.

In addition to the ignition system, thegenerator is very often a source of noisesignals. Rapidly reversing current with-in the armature winding, as well assparking at the 'brushes caused by adirty commutator, are definite factors.The voltage regulator contains two setsof points, and under normal circum-stances one of these sets is intermit-tently, but at high speed, interruptingthe field current in the generator withresultant arcs and noise. Usually in-struments or gauges are a minor sourceof noise, but on some installations theycan prove to be a major cause. Anothermajor offender is static electricity. Thiscan be generated by a fan belt whichhas not sufficient lubrication, or can begenerated by wheels rolling on the pave-ment. The static electricity phenome-non is more acute in a vehicle whichdoes not have good solid dc continuityfrom part to part.

There is a subordinate problem onany cab which can create additionalnoise sources. This comes about due tothe many resonant lengths of rods, fluidtubes, and wires within a car. If noiseis either conducted or radiated to thesewires, they will re -radiate the particularfrequency which corresponds to. theirresonant lengths very effectively. It willbe necessary in suppression to pay someattention to this problem.


Noise Suppression

COMMUNICATION SYSTEMS

Basic Suppression Requirements

While the suppression problem ap-pears to be enormous and the solutionmost difficult, it has been found thatgenerally speaking the two main sourcesof noise are the ignition system and thegenerator. Other sources may or maynot be an important factor in a par-ticular taxi, but in many cases suppres-sion of ignition noise and of the gen-erator noise will usually suffice toachieve a satisfactory noise level. Whenthis is true (and it will be in a largenumber of cases) it is only necessary toinsert resistor plugs into the ignitionsystem, a resistor in the distributor, anda coaxial by-pass capacitor on the gen-erator armature. In many high band(144-172 mc) systems, even the coaxialcapacitor on the generator armatureoccasionally proves unnecessary. It isonly after these 'basic techniques havefailed to solve the ignition noise prob-lem that it is necessary to go into theminor noise sources. If it becomes nec-essary to track down and eliminate noisefrom these other sources, then a sys-tematic procedure must be used alongwith proper techniques to solve theproblem as quickly and as completelyas possible.

Identifying Noise Sources

Much time can be saved if the sourceof the noise can be rapidly pinpointed.Since many of the noise sources are ac-tive only when the taxi is in motion,this is not always easy. Considerable ex-ploration is usually possible with the carstanding still, however, and certainsources of noise can either be verified or

by George A. Svitek,National Service Manager, Mobile Radio,General Electric Communications Products

eliminated. In searching for noise it isdesirable to feed a weak signal into thereceiver to just open the squelch. Aweak signal is more desirable than astrong one because it will not necessarilyeliminate the amplitude effects of thenoise signal and these can therefore beheard in the speaker.

Ignition noise can be easily identifiedbecause of its nature. It produces apopping crackling sound in the speakerand the rate of these pops is tied to theengine speed. Speeding up or slowingdown the engine will cause correspond-ing changes in the ignition noise. Fromthis standpoint we might say that igni-tion noise is a relatively uniform type.It is not, however, as uniform as thegenerator noise. Generator noise is char-acterized by a high pitched whine whichis a function of the speed of the gen-erator. Separating the ignition noisefrom the generator noise is easy, for itcan be accomplished by turning off theignition switch. This will immediatelykill the ignition noise, but since the gen-erator is still turning, the noise from thegenerator will still be present. It is en-tirely possible that noise from the voltageregulator is still also present. This noise,however, does not have the characteristicwhine of the generator and producessharp crackling popping sounds in thespeaker. These sounds occur not at auniform, but rather at a random rate,and as such can be distinguished fromignition noise. Further identification ofour noise source is now possible fromcertain logical considerations. If resistorplugs have already been added to theignition system, and the ignition noisepersists, then in all likelihood noise is

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being conducted back into the cab'swiring. A systematic search can bemade to see if this is so.

Chase the Trouble Away

Various "Noise Chaser" schemes havebeen tried with different degrees of suc-cess. One such scheme employs a longpiece of RG8 transmission line. One endis plugged into the receiver and the otherhas the external shield removed exposinga 78 inch length of the center conductor.A current meter with equally long leadsis plugged into the first limiter jack ofthe receiver under consideration, andcarried around with the RG8 probe.When the probe is placed near any wireor area which is radiating considerableinterfering signal, the limiter currentwill increase. If for some reason thelimiters become saturated, then the pick-up of the probe can be decreased bylooping over the center conductor andsoldering it to the braid.

A variation of this noise chaser usesan AM detector and audio amplifier asthe indicating source in preference tothe limiter current. Such a device willproduce an audible signal similar tothose encountered on AM radios, a tech-nique with which many radio tech-nicians may already be familiar. Theradio set itself can be used as an AMdetector by removing the 6AL5 in thesquelch circuit, detecting the incomingsignal at the limiter grid, and feeding itinto the audio amplifier. The methodusing the portable AM detector is moreeasily applied, however, because of thespeaker's being carried with the probe.In this manner various parts of thevehicle can be jarred to see if noise isbeing produced in audio output. Thisaffords a good means for finding looseor intermittent connections. It is alsoquite effective for finding noise gen-erated by the elements of the variousgauges in a car.

Noise due to static electricity is usuallygenerated with the auto in motion. Thismakes a detecting job more difficult.Two sources, however, can easily beidentified. The first is wheel static, andthe second tire static. Wheel static canbe detected by putting on the brakeswhile the car is in motion. If wheelstatic is present, it will disappear whilethe brakes are on. Leaving the pave-

ment and pulling the car onto theshoulder will eliminate tire static if itis present.

Detection of fan belt static is a littlemore difficult. Perhaps here the cure iseasier than the searching job, for properlubrication of the belt will minimizethe electricity generating capability.Static discharges which occur while thecar is in motion which can neither bepinned down to fan belt nor tire orwheel noise, can usually be cured bybonding. Unfortunately, there is nosimple way of detecting these noises andthe method for suppressing them isusually "cut and try." The most promis-ing areas to try bonding are fairly wellknown, however, which simplifies thistest somewhat.

Suppression Pitfalls

The main weapons in attemptingnoise suppression are by-passing orfiltering, and bonding. Both techniquesmust be properly understood and ap-plied, however, if proper results are tobe achieved. To understand this prob-lem we must answer the questions,"When is a by-pass not a by-pass?" and"When is a bond not a bond?" Foreffective by-passing, either coaxial ca-pacitors or very high quality paper ormica capacitors must be used. This isbecause poor quality capacitors haveconsiderable internal inductance. Thus,the capacitor can be represented by anR L and C in series. The larger the in-ductance the less effective is the capaci-tor when used as a by-pass. A typicalcondenser used for by-passing in theAM broadcast band has a peak by-pass-ing efficiency in the area of one andone-half to two megacycles. Attenuationdrops off very rapidly, however, at afrequency of two and a half to threemegacycles. This is because such acapacitor contains considerable internalinductance. To be an effective rf by-pass a capacitor must show a very lowimpedance to ground. This it cannotdo if it contains considerable internalinductance or has long leads connectingeither to ground or to the line being by-passed. The longer a lead is the moreinductance it contains. An element withhigh inductance does not present lowimpedance to ground but high impe-dance. For this reason it is absolutely

necessary to use high quality capacitorsas well as very short leads. Coaxial ca-pacitors are specially designed to havelow internal inductance, and are verygood by-passes up to the area of 1000me when used with very short leads.

In order for a bond to be effective, itmust meet two requirements. First, itmust present a low dc resistance be-tween the two members being bonded,and second it must present a low rfimpedance as well. It is a fact that anytwo members being bonded togetherwill have a certain amount of distributedcapacity between them. This can beeasily seen in the case of a hood and firewall. At the back the hood is insulatedfrom the body by a cloth strip. It can beseen that considerable capacity can existbetween these two members. This ca-pacity is in parallel with any bond whichis connected between them. If the bond-ing strap is long and has considerableinductance, we then have effectively aparallel tuned resonant circuit. Thus,instead of presenting a low rf impe-dance between the two members wemay present a very high rf impedancebetween them at the resonant frequencyof the trap. If we are unfortunateenough to have this frequency fall nearour receiver frequency, the bond will betotally ineffective. It can be readily seenfrom the two above examples that falseindications can be obtained by improp-erly applied techniques.

The third most important fundamen-tal technique is to always by-pass sourcesof noise close to the source. For instance,it does little good to by-pass the tempera-ture gauge at the dash of an automobilewhen the noise is actually being gen-erated within the heat -sensing elementof the motor block. In many cases, thisnoise has to travel a long length of wirebefore it reaches the dashboard. It willradiate over the whole length of thiswire and possibly into the receiver. Inorder to be truly effective gauges mustbe by-passed as near to where the actualelement is as possible. This same con-sideration applies to armature or regula-tor 'by-passes or to by-passes on theignition coil.

Suppressing the Ignition System

It has already been mentioned thatthe primary source of noise in the igni-

tion system is the spark plug. The situa-tion can be almost cured by using re-sistor plugs. Considerable bias existsagainst the use of resistor plugs in cer-tain areas. When properly applied, how-ever, these plugs are highly satisfactory,and the benefits to be achieved 'by theiruse from the noise standpoint certainlyoutweighs any small disadvantageswhich might result from their use.

Proper application of resistor plugsrequires first of all to use the correctplugs. It has been recorded for instancethat certain types of plugs give excellentlife and performance on cars of onemanufacturer, whereas other sparkplugs have given excellent service invehicles made by other companies. Re-sistor plugs can be identified by the plugnumber. If a set of non -resistor plugsis replaced by a set of resistor plugs, itis also highly desirable to check the timeof the engine. Failure to do this mayresult in sub -par engine performancewhich is in no way the fault of theplugs.

Suppression of noise generated in thedistributor is usually accomplished inthe same manner. Many distributorshave resistors built in, and if this is notthe case, a center tower resistor can beused. These techniques are effective onthe noise generated by the arcing fromdistributor rotor to stator. There is, how-ever, another point to be considered inconnection with distributors. An old dis-tributor with, perhaps forty to fiftythousand miles of operation will havemany tiny particles of metal imbeddedin the bakelite. These have been tornfrom the rotor and stator by the arcing,and they contribute to an overall noisysituation. Under these conditions thedistributor cap should be replaced, sinceengine performance will also be im-proved.

Resistance type ignition cable hascome into common use during the pastfew years and is very effective. Suchleads have been known to age and be-come brittle after a period of yearsthough, with a resultant breakdown intheir conductivity. Under such circum-stances the leads must also be replaced.A potential problem exists in the use ofthe steel stranded ignition cable. Elec-trical connection to the end ferrules ismade by crimping, and where this crimpis not effective, we have a possible source


of arcing. This can be cured by correct-ing the crimp or by replacing with igni-tion cable which can be soldered andsoldering all the ferrules.

The breaker points in the ignitionsystem are also a source of potentialnoise. Arcs in this part of the circuit are.usually quenched very quickly by thecapacitor. If the point setting is incorrector if the capacitor is old or of impropervalue, arcing will be more severe thannecessary, with resultant increase inignition noise,

The coil itself is not usually a sourceof ignition noise. It can, however, pickup ignition noise from the ignition wir-ing and re -radiate it, particularly if thebody of the coil is not properly groundedto the vehicle frame. In many cases itwill happen that the metal body of thecoil has been painted and placed in astrap which is grounded to the frame.There is no DC contact between thebody and the bracket and the coil willradiate noise. This can be cured by re-moving the coil and scraping the bodyof the coil clean along with the insideof the bracket and then replacing. Witha plastic -cased coil, it is sometimes nec-essary to completely enclose the coilwith a metal shield.

To keep the ignition noise penned upunder the hood, it is desirable to placea coaxial by-pass capacitor in the bat-tery lead to the coil primary located asclose to the coil as possible. Such a ca-pacitor will prevent ignition noise frombeing conducted out on the car wiringwhere it can find many lengths of wiresuitable for radiating to the antenna.

Generator Suppresion

In general the only suppression thatwill be required on the generator is thecoaxial capacitor, from the generatorarmature to ground. This capacitormust be mounted as close to the genera-tor armature terminal as possible, pref-erably on the generator body. Thesecapacitors come in fifty and one hun-dred amp sizes and a value of about onehalf microfarad usually works very well.If such a capacitor proves ineffective, itis a good idea to check the generator. Inall likehood the generator has not re-ceived any maintenance for a consider-able period of time and cleaning up the


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ELECTRONiiC SERVICING * JUNE, 1957 11

The Case of The ServicemanWHO KEPT IT CLEAN !

The fringe area Jones family wantedTV entertainment but got "snow".When Junior's favorite show wasruined once too often, the service-man was called in.

Thanks to theservicemanand Jerroldthe Joneses gethigh fidelitycolor andblack andwhite picturesevery time!

He pointed out that even with a goodantenna weak signals are affected byline loss and noise, making good re-ception impossible . . . recommended aJerrold DE-SNOWER.

Antennamounted, the DE-SNOWER cap-tures the signalbefore loss andnoise affect it, de-livers it to the setover shieldedcoax . . . provid-ing snow -freepictures.

THE JERROLD DE-SNOWERA high profit pre -amplifier accepted everywhere!Combines 25 db gain with low noise input-only6 db. No AC outlet or separate wiring on mast.

Available in 3 models-Single Channel; Broadband Chs. 2-6, Broad-band Chs. 2-13. Packed complete with remote 24 volt power supply.See the DE-SNOWER line at leading distributors or write direct forillustrated brochure to: Dept. P. D. # 8

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LOOK TO JERROLD FOR AIDS TO BETTER TELEVIEWING

TV Cooking Bench

Insures Satisfactionby Harry J. Miller

Good will is created and needless call backs avoided

by the pre -testing procedure described in this article

tttHELL hath no fury like a woman

scorned!' aptly describes thestate of mind of a customer who haswaited years to buy a television set,then has trouble with it right after de-livery," says James H. Yergey, whomanages the TV and Appliance de-partment at Webb's City, largest storein St. Petersburg.

To prevent this catastrophe, the Flor-ida manager never permits a video setto get out on the showroom floor, or tobe delivered to a customer, until it hasbeen parked on a "Cooking Bench."

The bench is a series of compartments

into which new sets are moved directlyfrom their packing cases and hookedup across the line. "For 48 to 72 hours,"said Yergey, "we let these sets fry.Sometimes a tube is missing or a partrequires adjustment or some fault hasdeveloped during shipping. In any case,we line them up and turn them on."

From time to time during this pre-test, the service foreman will examinethe operating set to see if anything hasdeveloped to warrant pulling the chas-sis. This can be done on the spot, thusavoiding the embarrassment of havingto yank a chassis a few days after de -


IN GLAMOROUS NEW YORK CITY-ALL EXPENSES PAID PLUS $100 CASH

livery. Result-fewer comebacks, fewerservice calls, and a more satisfied cus-tomer.

"If we're having a sale on a particu-lar number," said Yergey, "we line upthe models of that number and turnthem on to find out how well they'reworking. Should a set be delivered to acustomer, and the serviceman sent toanswer a complaint find a major repairis necessary, we send out a new chassisthe very next day, and yank the faultyone for repairs in our shop. Nothingmakes a new customer happier than thisaction, and nothing makes him unhap-pier than to have a number of repairson his set right after he's bought it. Inthis way, we've eliminated at least 25%of needless service calls.

"Another thing we do that keeps ourcustomers satisfied, is to give each buy-er a warranty that begins the day theset is installed, not the purchase date.Very often, this few days' difference intime may result in a set conking outjust out of warranty, and this isn't fairto the customer.

"Within 30 days after a new set hasbeen installed, we send a man out on a"courtesy call,'' regardless of whetheror not we've heard from the customer.On this occasion, the serviceman checksthe set's performance and the ability ofthe customer to set the controls.

"We've found that old people espe-cially-and they comprise many of ourcustomers-don't get the hang of tun-ing properly, nor can they adequatelyfollow the information in the set's in-struction book. Our technician reviewswith them the set's operation."

The TV setup in this giant Floridastore is broken down into three units;an antenna crew which does nothingelse; a 'make-ready' crew which checksall incoming sets and operates the cook-ing bench; and finally, there is a repairdepartment of top technicians. Shouldthe 'make-ready' department find anyminor defects in a new set, they do therepairing. If the job is a major one orelusive, it goes to the experts in the re-pair department.

St. Petersburg is a town of retiredpeople, and these oldsters chat for hourstogether on the town's benches or attheir trailer camps. "Word of our serv-ice soon spreads," said Yergey. I I

WAN A WEEKEND A' THE WALDORF FOR 2IN THE PYRAMID TWIST -MOUNT CAPACITOR CONTEST

TOTAL -147 WONDERFUL PRIZES-PLUS A PRIZE TO EVERY ENTRANT ... SERVICEMEN, ENTER NOW YOU CAN'T LOSE!

IT'S EASY TO WIN ANY ONE OF THESE WONDERFUL PRIZES:

GRAND PRIZE: Weekend at New York's fabulous Waldorf Astoria Hotelfor 2, guest of Pyramid. Air transportation from your home to New Yorkand return. Weekend of entertainment including a visit to the famousGaslight Club, dinner at the Waldorf's Starlight Roof, and breakfast atthe Waldorf. Air transportation by CAPITAL Airlines Viscount.

1St PRIZE: One 4 -drawer steel file cabinet plus your choice of 50 sets

of PHOTOFACT folders. Value: $120.45.

FIVE 2nd PRIZES: 5 CR-30 PRECISION Cathode Ray Tube Testers. dlr.

net $109 ea.

TEN 3rd PRIZES: 10 CRA-2 PYRAMID Capacitor -Resistor Analyzers. dlr.

net $92.50 ea.

TWO 4th PRIZES: 2 SW -54 NATIONAL Short Wave Receivers. dlr. net

$59.95 ea.

TEN 5th PRIZES: 10 JENSEN professional speaker units consisting ofa D-30 lifetime driver unit and RT-20 rectangular horn. dlr. net $44.40per set.

FIFTEEN 6th PRIZES: 15 TW CHANNEL MASTER 7 element "travelingwave" TV antennas, Model 350. dlr. net $33 ea.

EIGHTEEN 7th PRIZES: 18 PYRAMID Pyra-Pak kits consisting of $69.95in Pyramid capacitors, metal tool box and tool kit. dlr. net $29.95.

THIRTY-FIVE 8th PRIZES: 35 PYRAMID gift certificates entitling you/) $10. (dir, net) of Pyramid capacitors at your distributor.9th PRIZE: WALCO twin -point diamond phono needle. dir. net $30. For

G.E. Var. Rel. Cartridge.

FIFTY 10th PRIZES: 50 WALCO needles for G.E. twin -point sapphires.

$3.50 dlr. net.

AND to all entrants a kit of 5 bypass and coupling capacitors featuringthe Pyramid type IMP.

It's easy to win any one of 147 big prizes-just follow these simple rules:Identify the unnamed Pyramid T -M capacitor in the TV set schematicappearing on this page. Give the Pyramid stock number, name and modelnumber of TV set. Then mail your entry to Pyramid. Use coupon on thispage or obtain additional blanks from your distributor. A differentschematic will appear in these servicemen's magazines for 4 months.Prizes will be awarded on a points -earned basis as follows: 5 points forContest No. 1; 10 points for Contest No. 2; 15 points for Contest No. 3;20 points for Contest No. 4; and 10 points each contest for neatness.Possible perfect score: 90 points. However it is not necessary to achieve

a perfect score to be declared a prize winner.

So act quickly...send in your entries early each month...you can't lose.

CONTEST No. 4

086 1245467 654 17L8P4

Identify C2,A,B,C,DCONTEST CLOSES JULY 15,1957

A PHOTOFACT STANDARD NOTATION SCHEMATIC 0 Howard W Sams 8 Co., Inc.

JUDGES: M. Harvey Gernsbeck, editorial director, Radio -ElectronicsOliver Read, D.Sc., publisher, Radio & Television NewsHoward W. Sams, chmn. board, Howard W. Sams & Co., Inc.

HELPFUL HINTS

The unidentified capacitor in each entry will be a Pyramid Twist -Mount.All schematics are of TV sets made in the U.S. by a known manufacturerwithin the past 2 years.

Schematics for reference may be those published by the TV set manu-facturers, Howard Sam's Photofacts, or by any other accepted publisher.You may enter as often as you like but be sure to include a box top(showing stock number) of any Pyramid Twist -Mount Capacitor, with yourletterhead or business card with each entry.

WHO MAY ENTER

Any Radio -TV serviceman or employee of a Radio -TV service companymay enter. Officers, employees, (members of their families) of PyramidElectric Co. or its advertising agency are not eligible to enter the con-test. All entries are limited to residents of the continental U.S. over21 years of age.

All entries become the property of Pyramid Electric Co., none will bereturned and the decisions of the judges are final. In case of ties,duplicate prizes will be awarded. This contest is subject to all federal,state and local laws and regulations.

A WEEKEND AT THE WALDORF FOR 2QP CAPITAL AIRLINES

PHOTOFACT FOLDERS

MAIL THIS ENTRY BLANK NOW!Pyramid Twist -Mount Contest, Dept 1Pyramid Electric Co.P.O. Box 655, Tyler Park Station, North Bergen, New Jersey

Entry No. (1) (2) (3) (4)-(check one)-isr. Pyramid stock No

Twist -Mount values

Set manufacturer's name TV set model NoI enclose a box top (indicating stook number) of any Pyramid Twist -MountCapacitor together with my business card or letterhead or my employer's,.

Contestant's name Position

Contestant's address

City Zone_State

Employer's Firm name

Employer's address

City Zone_State

My jobber's name and address

ENTER AS OFTEN AS YOU LIKE-FOR ADDITIONAL ENTRY BLANKSSEE YOUR JOBBER.

Capacitors, Selenium Rectifiers-for original equipment, for replacement

PYRAMID ELECTRIC COMPANY North Bergen, New Jersey


HAVING investigated the means bywhich minute audio signals are

amplified, equalized, altered and se-lected in high fidelity preamplifiers andcontrol chassis, we are now ready toexamine the "powerhouse" of the hi fichain -the basic power amplifier. Strict-ly speaking, the power amplifier of anyaudio system consists of a single, a pair,or more power output tubes, coupled toa transformer designed to match theplate impedance of the output stage tothe voice coil of a loudspeaker. Stand-ardization of terminology in the hi fi in-dustry enlarges quite a bit on thisdefinition, however. In hi fi, the poweramplifier (or basic amplifier) is a unithaving no compensation or tone con-trols (other than perhaps a pre-set inputlevel control), several voltage amplify-ing stages, a power supply section andfinally the actual output stage whichdoes the "power amplifying." There areseveral reasons for this rather arbitrarybreak -down. Really large power am-plifiers are very bulky affairs and aremeant to be "heard but not seen." Thatmeans that a physical as well as anelectrical separation between preampli-fier (which houses the customer con-trols) and amplifier is desirable. Itwould be neither practical nor desirableto transmit the large driving voltagesacross long lengths of cable from oneto the other. On the other hand, thereis a practical limit to the "low signal"side, below which the signal to humratio problem would become important.As a rule, the voltage necessary to drivethese basic amplifiers to full output fallsanywhere between about .75 to 3.0 volts.This range of voltage amplitude is greatenough to be beyond the hum problem,yet small enough to be handled by inex-pensive shielded audio or microphonecable. Thus, preamplifier control chassisequipped with cathode followers (seeFebruary issue of SD) may be separatedby distances of several hundred feetfrom the basic amplifier. It should benoted at this point that not all amplifiersare so divorced from their associatedpreamplifiers. In recent years the twounits have been recombined on onechassis with great success. Generally,however, these units will have muchlower power ratings than their sepa-rated counterparts, because of spacelimitations in design. Regardless of the

Power Amplifiers

in Hi fiby Lawrence Fielding

The procedure used in determining the requiredpower output of an amplifier is discussed in thisinstallment. The measurement of power responseand sensitivity are also treated.

format used, we shall consider the am-plifier portion of a system to be thosestages following all tonal compensationand equalization whose sole function isamplification and final presentation tothe terminals of a loudspeaker systemfor reproduction.

Selling Power Output

Long experience in this field hasshown that a hi fi customer is like noother consumer in the world. You, as ahi fi service dealer, will be sought afternot only for repair work but for earnestconsultation and advice. One of themost serious questions you will be askedis: "How much power do I need in apower amplifier for good reproduc-tion?" There is, of course, no single an-swer to this question, so at this point letus consider the problem in some detail.One watt of acoustic power would beenough to fill an auditorium having1,000,000 cubic feet with sound equalto that of a symphony orchestra playingat average volume. Why, then, do wesee amplifiers on the market havingratings of 25, 50 or even 100 watts ofaudio power and being eagerly boughtby the public? Well, in the first place,we said that one watt of acoustic powerwould fill an auditorium, but acousticpower is not electrical audio power.There's a loudspeaker in between, andby far the most inefficient unit in the

entire hi fi chain is the loudspeaker.Efficiencies of the order of 10% forthis component are considered highand some popular speakers are de-signed with efficiencies as low as Y2 of1%. It can be readily seen that aspeaker of the latter type, when fedwith 10 watts will only produce .05watts of acoustic energy, enough to filla 13,000 cubic foot volume of space.Still more than most living rooms, butwe're not finished. We spoke of anorchestra playing at average loudness.We must add another 20 db or so for

cymbal crashes, drum beats and othercrescendos. 20 db represents a changeof power of 100 to one. Putting it an-other way, this maximum energy of.05 watts would now take care ofabsolute peaks in a room having avolume considerably Mess than 1000cubic feet and a one thousand cubicfoot living room is one that measures,say about 10' x 10' x 10', so we're introuble with a ten watt amplifier usinga low efficiency speaker. There is apractical way to calculate power re-quirements, by which you can intel-ligently advise prospective customers inthe choice of a power amplifier.

Calculating Power Amplifier Ratings

Referring to Table I you will notethat acoustic power requirements arelisted for various sound levels and forvarious cubic enclosures. It should benoted that 80 db corresponds to averageconcert hall volume. Not everyone willwant to play music that loud in thehome (and even if they do, the neigh-bors wouldn't permit it). Explain thisto the customer and get his opinions in

Suppose he decides that 70db is all he will ever want in the livingroom. Add 20 db for peaks in themusic and possible differences in fur-nishings (draperies, sound absorbingrugs, etc.) between his living room andthe "average" for which this table wasderived. This makes a total of 90 db.

TABLE

Volume

or Intensity

Level

CUBIC FEET

1000 2000 3000 4000

55db

60db

65db

70db

75db

80db

90db

100db

110db

.0000051

.000016

.000051

.00016

.00051

.0016

.016

.16

1.6

.0000098

.000031

.000098

.00031

.00098

.0031

.031

.31

3.1

.000014

.000045

.00014

.00045

.0014

.0045

.045

.45

4.5

.000019

.000059

.00019

.00059

.0019

.0059

.059

.59

5.9

Acoustic

Power

Requirement

in Watts

14ELECTRONIC SERVICING JUNE, 1957

Calculate the cubic volume of the lis-tening area (to the next largest 1000cubic feet, as shown in the table). Sup-pose it is about 3000 cubic feet. Con-sultation of Table I shows that 0.45watts of actual acoustic power will berequired to meet these conditions. Next,determine the efficiency of the loud-speaker system the customer proposesto use. (This specification is beginningto appear with increasing regularity inthe "spec" sheets put out by loudspeakermanufacturers.) Suppose the efficiencyis 1%. Then divide .045 by .01 (effi-

ciency expressed as a decimal) and wecome up with tl-ie answer of 4.5 elec-trical watts of audio power. Even a fullsafety margin of 2 to 1 would still meanthat a ten watt package will fill the billwith power to spare. To advise such acustomer to get a high-powered jobwould be doing him an injustice. Thereare, of course, exceptions even to thisscientific approach. Find out whetherthe customer plans to add differentspeakers in other rooms at a futuredate, all to be operated from the samesystem (and very likely, all operating atonce under certain circumstances). Ifsuch proves to be the case the wholepower pictures changes accordingly.

NEGATIVE FEED-

NETWORKBACK

DRIVER POWER

STAGE OUTPUT

INPUT VOLTAAMPLIFIER

-1-0

-0PHASE

INVERTER

PUSH-PULL

OUTPUT

TRANS-

FORMER

o----

DRIVER POWER

STAGE OUTPUT

Fig. 1-Flack diagram of stagesin a typical power amplifier.

Circuit Elements

The various circuits which comprisea power amplifier are illustrated inblock diagram form in Fig. 1. Each ofthese elements will be treated in greaterdetail in future articles. For the timebeing, there are several overall measure-ments which you will he required tomake in connection with the properservicing of amplifier and these will


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trade flashesA medical milestone was marked recently with the in-troduction, at St. Luke's Hospital in Chicago, of a"surgeon's eye" technique that brings medical students asclose to an incision as the doctor's own elbow. Manu-factured by Dage Television, Division Thompson Prod-ucts, Incorporated, Michigan City, Indiana, full -color,closed-circuit television is the device that makes thispossible, transmitting to students many floors away thelife -and -death immediacy of the surgical routine. Thedoctor's commentary, simultaneously transmitted, in-forms them as well of the special problems attendantupon each individual case.

Cumulative television figures compiled during thefirst quarter of this year amounted to 1,474,729receivers compared wtih 1,844,632 made duringthe first quarter of 1956. Television sales totaled534,115 in March compared with 525,437 sold inFebruary and 544,411 sold in March 1956. Cumula-tive television sales totaled 1,682,911 this year asagainst the 1,689,178 sold in the correspondingquarter of 1956.

The transistor industry is now 2.7 times greater than itwas at this same time last year. Factory sales of transistorsin March totaled 1,904,000 units with a dollar value of$5,321,000 compared with 1,785,300 sold in Februarywith a dollar value of $5,172,000. Cumulative sales ofthe semi -conductor device during the first quarter of thisyear amounted to 5,125,300 units with a dollar value of$14,612,000 compared with the sale of 1,898,000with a dollar value of $5,688,000 during the corresrn 'ing quarter of 1956.

o o

Figures show 3,959,367 radios were produced thisyear compared with 3,532,243 at this time last year.Sales totaled 730,584 in March, excluding auto sets,compared with 525,029 sold in February and 527,649sold through retail outlets in March 1956. Cumula-tive radio sales increased to 1,818,976 over the 1,-513,722 sold during the first three months of lastyear. Since the bulk of car radios produced are solddirect to automobile manufacturers for installationin new cars, RETMA does not include such radiosin its count of retail radio sales.

125,041,000 receiving tubes worth $104,808,000 duringthe first quarter of this year shows a substantial increaseover the 120,420,000 tubes worth $96,919,000 sold inthe corresponding 1956 quarter. Television picture tubesales in March totaled 833,088 units valued at $14,847,-798 compared with 728,363 such tubes sold in Februarywith a dollar value of $13,134,778. Cumulative TV pic-ture tube sales during the first quarter of this year totaled2,322,306 with a dollar value of $41,577,018 comparedwith 2,638,503 tubes with a value of $49,867,451 soldduring the corresponding quarter of last year.

o

Robert F. Halligan, vice president in charge ofoperations at the Hallicrafters Company announcedtwo new appointments. Cletus A. Wiot has beenpromoted to director of personnel and Anthony R.Dambrauskas to national service manager. Bothpromotions, Halligan said, were made to strengthenthe operations of the personnel and service depart-ments in line with Hallicrafters expansion program.

The Blonder -Tongue Labs. Inc., has moved to largerquarters. The new building is located at 9-25 AilingStreet, Newark 2, N. J.

According to Leonard Ashback, who spoke at a recentNARTB meeting, FM is enjoying a revival because of`1-, poor quality programs on AM radio and television.

.:.e present trend continues, FM sets will outsell AMcts within ten years. Ashback said, "We are getting the

radio back into the living room and the TV sets aregoing to the bedrooms and dens.

o

"Because 960 out of every 1,000 portable television setssold have 14 inch screen sizes with 96 sq. in. viewablearea and larger, Hotpoint will concentrate in 1958 onlarger portables, namely, 14- and 17 -inch sets with morethan 96 sq. in. viewable area." This statement fromHoward IV. Hibshman, marketing manager, televisionreceiver dept., Hotpoint Co., was made as the companyprepared introduction plans for its new 1958 portabletelevision line.

Ram Electronics has expanded its engineering andproduction facilities and has moved to new andlarger quarters at 600 Industrial Avenue, Paramus,New Jersey.

The General Electric Company announced a reorganiza-tion of its high-fidelity sound components operations, toresult in "increased concentration on technical develop-ment and sales efforts" for the products. Responsibilityfor engineering, manufacturing, and marketing of thehi-fi products is being transferred from the company'sTV Receiver Dept., Syracuse, to its Specialty ElectronicComponents Dept., in Auburn, N.Y.

Paul Jackson, President of Jackson Electrical Instru-ment Company of Dayton died in that City on Saturday,April 27th. Mr. Jackson was a pioneer in the manu-facture of test equipment for the radio and televisionservicing industry. The business which bears his name

tube testers,and other equipment.

Scientists at Raytheon Manufacturing Company'sFood Laboratory are using radar's electronic energyto preserve fresh and cooked foods so they can bestored on a kitchen or grocer's shelf at room tem-perature indefinitely without refrigeration. Still inthe laboratory stage, the new process is expected tomake available normally perishable meats, fish,fruits and vegetables in unfrozen form the yearround without loss of flavor, texture or nutrientvalue.

Flying by means of "electronic road maps," helicopterscan now operate completely on instruments in cities, theopen country or in remote areas according to flightdemonstrations by Bell Helicopter Corporation and thePacific division of Bendix Aviation Corporation. Militaryand civilian aviation experts recently witnessed threedays of blind -flight demonstrations at the Bell Helicopterplant here that "dramatically prove the helicopter cannow make full use of its unique flying abilities regardlessof weather and visibility." The new flight aids made itpossible for the helicopter, which can hover in the airof weather and visibility."


DISKS TUBULARS

PLATE

ASSEMBLIESHIGH -VOLTAGE

CARTWHEELS

IIER01/1111CERAMIC

CAPACITORS

You can be sure that Aerovox Ceramic Capacitors

are exactly right for your service applicationsbecause of the extra -care taken in the manufac-

turing of these capacitors to provide you withtrouble -free, exact -duplicate replacements. This

extra -care assures your customers of stay -put

installations saving you time and money on costly

call-backs

The Aerovox line of ceramic capacitors is the

most complete on the market. A type for every

application is available to you for prompt delivery

from the com)lete stock selection carried by your

local Aerovox Distributor.

DISTRIBUTOR DIVISIONNEW BEDFORD, MASS.

trz Conado AEROVOX CANADA LTD Hamdton, OntExport. Ad Artrterno Inc T9 Brood St., Nnkr York, N Y

Coble Auxterno, N, Y

Video Speed c.Ceittac Spie*fra DATA SHEETS

Mfr: Emerson Chassis No. 120292 P, V

Card No: EM 120292-1

Section Affected: Horizontal and/or VerticalSweep.

Symptoms: Intermittent operation of horizontalhold, Vertical Sweep, or both.

Cause: Intermittent contact between etchedcircuit sweep board and chassis.

What To Do:Tghten screws which secure etched board to

the chassis. (Each screw grounds a separatecircuit.) If this doesn't work, make an elec-trical connection which will be solderedfrom the component C-43, to chassis ground.

Mfr: Emerson


Section Affected: Horizontal Sweep.

Symptoms: No brightness.

Chassis No. 120292 P, V

Cause: Defective condenser in grid circuit of theHorizontal oscillator.

What To Do:Change: C-44 (330uf-500V).

Mfr: Emerson


Section Affected: Video


Symptoms: Streaking or tunable R F interfer-ence on channel 1;6 when using a built inantenna.

Reason For Change: To eliminate interferenceon channel 1#6.

What To Do:Change: R-97 from 1000 ohms to 4700 ohms.Add: a 22 mmf condenser between pins $;6

and #7 of the 3rd video if tube (3CB6).

EMERSON

HEXSCREW

STRIPPEDSOCKET'PREVENTSGOODGROUND

CONNECTION

C43

ADD JUMPERTO GROUND

V2 6CG7HORIZ. 0 S C.

HORIZ.FREDCOIL

C44TO

HORIZ.PHASE

150K COIL

330K

30863D VIDEO IF

33

EMERSON Video Speed Swzvecutf Soistem4 c DATA SHEETS

1/2 6CG7VERT. OSC.

33K .0047,uf7

/

VERTICALHOLD CONTROL

1.5MEG CHANGE

TO LOCAL DISTANCE

TUNER

Bt FIL Bt FIL AGC

® O0 0

ADD.0/ Al f

4.7 MEG.

470 K

.001,a f

34

Mfr: Emerson


Section Affected: Vertical Sync. Circuit.


Symptoms: Vertical control holds at one endonly. Possible vertical jitter and/or poorvertical sync.

Cause: Aging components.

What To Do:Change value of resistor in series with verti-

cal hold control from 470K to 680K or 1 megto produce a point of hold in the center ofcontrol rotation.



Section Affected: Picture

Symptoms: Picture bounce at high audio out-put levels.

Cause: Leakage of audio coupling condenserallows audio output tube to draw grid currenton peaks of loud passages which causes achange in picture size.

What To Do:Change C-26 (.047 uf).



Section Affected: Video

Symptoms: Hum bars in picture on weak sig-nals. Not apparent on blank raster.

Cause: Hum is entering the rf thru agc line.

What To Do:Add a .01 uf condenser from the agc tuner

feed, (terminal A) to chassis ground.

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A.0OUTPUT

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OUTPUT

WATTAGE

DEALERPRICE

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SAINT PAUL I, MINNESOTA -U. S. A.

This is the housethat Jack built.

This is the clatterthat came from the housethat Jack built.

For all was the matterwith the musical clatter,that came from the housethat Jack built.

This was the platter?Which made all the matterwith the musical clatter,that came from the housethat Jack built.

Reviewing the data'twas not the platterwhich made all the matterwith the musical clatter,that came from the housethat Jack built.

The diffitulty was traced and-was found to arise from theloudspeaker. It was promptlyreplaced with a Norelco FRS

Speaker; And now ...

This is the housewith the Norelco hornand the maiden who's ',via ,

no longer forlorn.

Her mate's lust for datadiscovered the platterwas not ere the matterthat made musical clatterthat came from the housethat Jack built.

""4.

fioreko*cW_Rei. Speakers are availablein 5", 8" or 12" sizes in standard imped-ances. Priced from $6.75 to $59.98.

ADD TO... and improve any sound systemwith 0/1/oreko.® *FULL RESPONSE SPEAKERS

Write today to Dept. E6 for brochureand prices of these unique speakers.

NORTH AMERICAN PHILIPS CO., INC.High Fidelity Products Division

230 Duffy Ave. Hicksville, L. I., N. Y.

Videa Speed Swtoici01,9 go/stem/1 DATA SHEETS

Mfr: Muntz Chassis No. 49A4

Card No: MU 49A4-1

Section Affected: Sync.

Symptoms: Unstable vertical lock.

Reason For Change: To improve vertical hold.

What To Do:Rewire 25 volt filaments so that they are in

the order shown in diagram.

Mfr: Muntz

Card No: MU 49A4-2

Section Affected: Raster

Symptoms: Blooming.

Chassis No. 49A4

Reason For Change: Circuit improvement-Increase 1X2 filament voltage.

What To Do:Remove R68 (2.2 ohms).

Mfr: Muntz

Card No: MU 49A4-3


Symptoms: Unstable horizontal sweep.

Reason For Change: Circuit improvement.

What To Do:Change: R74 (12K) to 10K.Also: C68 (.01) to .luf.

Chassis No. 49A4

MUNTZ

V/2 V725AX4 V I 0 25L6 V 8

25806 25 L6

T4

VIII X2B

R68 -Ali-REMOVE ANDCLOSE CIRCUIT

35

MUNTZ Video, Speed Swum:cuff, &Stems © DATA SHEETS

V/O25BQ6

HOR. OUT.

C58

V912AU7

NOR. A FC-OSC.

R59

Mfr: Muntz

Card No: MU 49A4-4


Chassis No. 49A4

Symptoms: Drive lines present with certain25BQ6 output tubes.


What To Do:Change: C58 (.005-500V) to .001uf 500V.

Mfr: Muntz

Card No: MU 49A4-5


Chassis No. 49A4

Symptoms: Poor hold range with changes ofV9, 12AU7.


What To Do:Change: R61 (10k) to 18k.

Mfr: Muntz

Card No: MU 49A4-6


Chassis No. 49A4

Symptoms: Difficulty in adjusting horizontalhold.


What To Do:Change: R59 (220K) to 180K.

USE LOW COST

IMPEDANCEMATCH

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i m prove receptionas much as 6dbEliminate Signal Losses, Smear,Ghosts and Other Picture -De-grading Conditions ResultingFrom Antenna -to -Line or Line -to -Set Mismatch.

B -T BALUNmodel MB

$list

Mounts on antenna mast or strut.Provides exact impedance matchbetween 75 -ohm unbalanced lineand 300 -ohm balanced line orantenna. Has 75 -ohm coax fittingand 300 -ohm screw terminals.Built into weather protectingcowl housing.

B -T TV SET MATCH55t1model TM j --list

Used at TV receiver to match 75 -ohm cable to 300 -ohm TV set in-put. Cable plug and lack permitquick, easy disconnect. Hasheavy duty, 300, -ohm outputleads.

At electronic parts distributors.For complete accessory catalog,write fo Dept. 0-6.

BLONDER -TONGUE LABS., INC.9.25 ALLING STREET. NEWARK 2, N. J.

36

THE WORK BENCH

Unusual Service Problems And Their Solutions

by PAUL GOLDBERG

Service Mar ager

WHEN servicing printed wiringpanels, carefulness is of utmost

importance. There are many excellentkits containing specialized tools, specialsolder, lacquer and lacquer solvents inorder to accomplish a perfect repair job.The most important thing to rememberhowever, is to work slowly and care-fully.

Ph ilco TV -440

The receiver was turned on and it wasnoted that there was neither video andnor sound. The customer had com-plained previously of intermittent videoand sound. The 1st and 2nd video iftubes, 6DE6's were replaced individuallybut had no effect. As the 6AM8, the3rd video if and 2nd detector was aboutto be removed from its socket for check-ing purposes, the video and soundpopped in. Upon pressing lightly onthe 6AM8 the video and sound againdisappeared. This receiver utilizes a

separate printed if panel for the 1st,2nd, and 3rd if stages, the second de -

/ST VIDEO

IF 60E6BD V/DEN

FFSDE6

PRINTED IF PANEL

90

°Z.

6A118

1/2 GAME3D IF

05

RACK CAUSINGBAD CONNECTION

80

i 20 VET1/2 6AM8

5

This Month's Problems:Printed Circuit Troubles;Sync Difficulties

tector, and their respective circuits.Pressing lightly on the 6AM8 a fewtimes, we deduced that the printed wir-ing was opening intermittently. Wenext removed the screws and the fourconnections from the if panel and ob-served the connections on the undersideof the 'bakelite panel. While holdingthe if panel and pressing on the 6AM8,we noted a slight crack in the bakelitewhich swept across one printed connec-tion. (See Fig. 1). It was the printedconnection from pin 8 of the 6AM8 tocapacitor C205 that had a tiny crackacross it. Thus any vibration wouldcause this connection to open. Using alow wattage soldering gun and work-ing slowly and carefully, the break wassoldered over. Now pressing on the6AM8 or the 6DE6's did not cause theprinted wiring to open. The printedpanel was re -installed and the receiverfunctioned properly.

Admiral Chassis 17Z3D

The receiver was turned on and itwas observed that there was no raster,but the sound was normal. The high

1/2 SANGVIDEO AMP

TOP V/EW

C32I

R33//20K Br

BRIGHTCONTROL

0321

SIDE VIEW BOTTOM VIEW

Fig. 1-Crack in printed wiring caused Fig. 2-Leaky C231 caused loss of rasterintermittent in Philco. in Admiral 17Z3D.

voltage arc from the 1B3 filamentseemed to be sufficient. The diagram(Fig. 2) was consulted and it was seenthat the video signal and brightnesscontrol voltage were fed to the cathodeof the CRT. The voltage at the cathodeof the CRT was then measured as thebrightness control was varied. Thevoltage readings measured too high.However, when the voltage was meas-ured at the center arm of the brightnesscontrol the voltage was closer to beingcorrect. This could not be a cathode toheater' short, since the cathode voltagemeasured high. We then eliminatedthe possibility of any other inter -elementshort by installing a series picture tuberejuvenator in its place. When thevoltages remained the same we deducedthat capacitor C321, .22 mf, was leaking.C321 was mounted vertically on a

printed circuit wiring board. It wasunsoldered and then resistance ,checledfor leakage. It was found to be -leakingabout 500K. We obtained the exact re-placement and installed it, workingslowly an dcarefully to avoid solderdrippings. The receiver was then turnedon and functioned properly.

Crosley Chassis 386

The receiver was turned on and itwas observed that the picture was tear-ing horizontally and skipping vertically.Because this was a composite sync prob-lem V109, 6SN7, the sync clipper inFig. 3 was replaced but had no effect.

The diagram was next studied. It wasnoted that a portion of the compositevideo signal is taken from the plate side

of the video amplifier (6AH6) plateload resistor R121 and fed to the gridpin 1$1 of the 6SN7, 1st Sync clippersection of V109 through R124, C122,R125, C123.

The signal that appears at the gridis positive in polarity and drives thegrid pin #1 of the first sync clipper verypositive, the grid current charging C123negatively. This tube's bias is obtainedby grid rectification of the video signal.The voltage drop across R126 biases thetube so that plate conduction occurs onlyon the peaks of the video signal. Sincethe maximum amplitude of the videosignal is actually the sync pulses, onlythe sync pulses appear at the plate pin1t2 of the 1st sync clipper. The negativegoing signal is applied through C125to the 2nd sync clipper. The 2nd syncclipper is biased so that any noise pulsesthat would appear at the negative por-tion of the pulses would drive the tubebeyond cutoff. Thus it limits the ampli-tude of the sync pulses and clips thepeaks caused by noise pulses.

Knowing these facts the scope wasset up and a waveform was measuredat pin #1 of V109 to ground. The scopeshowed a much smaller (1/10) wave-form than the diagram called for. (Referto diagram). A waveform was nextmeasured at the junction of C122 andC123. Here the waveform was correct.C123 was next checked and was foundto be OK. C124 was next resistancechecked and was found to have a leak-age of about 200K. C124 was replacedwith a new 22 uuf condenser and thereceiver functional properly. IN III

V108

6AH6VIDEO AMR

5

R1214.7 K

R124

8+ 8+

PIN No.1 1st.V109 \ SYNC\ CLIPPER\

C122.,, \y,

----).. 1

R125 C124 126

22 ,upfdZ2/TMEG.AR_

Leaky

C123 1

V109

6SN7

2nd.SYNC

CLIPPER

2

C125

Fig. 3-Leaky by-pass condenser caused loss of horizontal and vertical sync in theCrosley 386 chassis. A partial sync circuit scehmatic is shown.


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ASSOCIATION

National Alliance of Television and Elec-tronic Service Associations (NATESA)

The NATESA Board of Directorsmeeting at New Orleans was a hugesuccess. Present were over 100 Directors,Alternates and guests from points aswidely separated as San Mateo, Califor-nia, Buffalo, New York and Miami,Florida. The one day session was held inconjunction with a regional open seriesof seminars on technical and businesssubjects conducted for all area servicepeople by the host Affiliate, RETA ofNew Orleans. A special committee onlicensing was set-up to prepare a

brochure on licensing. It will be a "do'sand don'ts" publication.

Empire State Federation of ElectronicTechnicians Associations (ESFETA)

ESFETA held its election of officers.Gordon Vrooman of the Syracuse TVTechnicians was reelected President.Robert Larsen of the Valley StreamRadio TV Guild was elected Vice Presi-dent. Pat Pratt of the TV ElectronicService Association was reelected Treas-urer.

California State Electronics Association

CSEA'S drive to license service deal-ers in California ran into a delay lastmonth when a hearing on the bill wasrescheduled. Committee membersvoted to consider the measure at an-other date because four members of thegroup were absent. Anthony J. Anatasi,CSEA legal counsel who is guiding themeasure, said that although five votescould send the measure out to theSenote, it was decided to reschedule thebill and hope for full committee attend-ance at the session.

Long Island Guild

A bill licensing TV repairmen hasgone into effect in the city of LongBeach on Long Island. The Radio and


NEWS

by Samuel L. Marshall

TV Guild of L.I. won a major point inthe bill by having provisions written into protect the ethical serviceman fromdishonest customers. The Guild feelsthat the existing law is fair and protectsboth the serviceman and customer.

Radio TV Technicians Association, Pasa-dena, Calif. (RTA)

A regular technical meeting ofR.T.A.-Pasadena heard and saw a dem-onstration and lecture on "HorizontalSweep Systems." Irving Tjomsland,technical speaker from Triad Trans-former company, reviewed basic sweepcircuits, using a special "live" demon-stration board. He covered a step-by-step method for determining all hori-zontal sweep system (horizontal output& high voltage) troubles. The meetingwas then opened for a question andanswer session. Coffee and doughnutswere served before and after the meet-ing.

United Electronic Service Council

Meeting for the first time since thejoint industry conference, service leadersfrom the northeastern states gatheredat the Hotel Roosevelt in NewYork City to lay plans for future ac-tivity. The meeting was directed byFrank E. Silverman who, in additionto being president of the TelevisionService Associations, Inc., of Connec-ticut, is also chairman of the UnitedElectronic Service Council. The lattergroup is responsible for the initiation oftalks with officials of the National Elec-tronic Distributors Association whichgive much promise of cooperative ac-tivity between distributors and servicedealers. First order of business was theconsideration of a 20 -point industryprogram wh_ch had been submitted bythe Council of NEDA officials for theirapproval. It had been set aside at therequest of NEDA until such time asdubious legal aspects of some points hadbeen cleared by legal counsel.

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"Practical Radio and ElectronicsCourse," prepared under the directionof M. N. Beitman. This is a completelynew and revised edition of the famoushome - study training, incorporatingthree early volumes into a single largemanual. There are now 35 lessons in all.As in previous editions, explanatorynotes and teacher comments are printedin the narrow column alongside thetext. An answer booklet to the problemsis available for 25 cents. The "course"is priced at $3.95 postpaid.

A new brochure that describes thethree vital functions of General Elec-tric's magnetic engineering laboratory,was released recently by the MagneticMaterials Section of the MetallurgicalProducts Department, Erdmore, Mich.

A new catalog supplement sheet cross-referencing exact yoke, flyback, trans-former and coil replacements for BendixTV receivers has been released byRogers Electronics Corp., 49 BleeckerSt., New York 12, N. Y.

ATTENTION: People who service 2 -way Communications

PROCESSINGF6 Series Crystals

forSTANDARD 2 -WAY

Equipment in Commercial UseWire mounted plated crystals foruse in commercial equipment whereclose tolerances must be observed.All units are calibrated for thespecific load presented by equipment.HOLDERS: Metal, hermetically sealed.CALIBRATION TOLERANCE:

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TRADE

LITERATURE

The book, "Radio -Electronics MadeSimple" by Martin Schwartz, explainsthe subject of radio theory in a simple,non -technical manner. No previous ra-dio background is required. The moredifficult concepts of radio and elec-tronics are explained in everyday lan-guage. The book is complete in itscoverage of radio theory. It starts withbasic electricity and covers all phases ofradio right up through transmitters andreceivers. By going through the bookthe reader gains an excellent back-ground for further study of televisionand other specialized subjects. Pub-lished by the American ElectronicsCo., 1203 Bryant Ave., N.Y.C. Price$1.95.

John F. Rider Publisher, Inc., hasreleased a new 56 page T.V. TubeLocation & Trouble Guide. This bookshows the tube locations for all RCAtelevision receivers produced between1947 and 1956. It lists the tube comple-ment, key voltages and common trou-bles correlated with the tubes that maybe responsible for them. It also includesa complete chassis and model index.The price is $1.25.

"Repairing Television Receivers," byCyrus Glickstein, is a modern, andcompletely practical book on TV trou-ble shooting and repair techniques. Itpresents step-by-step, the procedure onon how to diagnose and troubleshoot afaulty TV receiver. It explains how tolocalize the defective section, then thedefective stage and finally, the defectivecomponent. A down to earth approachto successful TV servicing, covering theuse of test equipment, both simple andcomplex, with numerous practical illus-trations showing troubleshooting testsetups. Published by John F. Rider.Price $4.40.

"How to Install and Service Inter-communication Systems" by Jack Darr,covers the entire field of "intercom"systems in sufficient detail to enable thereader to do installation and mainte-nance work on this type of electronicequipment. It discusses the basic ampli-fiers, special speakers, switching ar-rangements, a -c and a-c/d-c systems,wireless systems, cabling networks, allcall systems, paging systems, remote andmaster systems, one and two way inter-com systems, installations for the homeand for industrial use, outdoor wiring,and system requirements for particularapplications. Published by John F.Rider. Price $3.00.

"Audio file," a catalog service forhigh fidelity dealers, completely cata-logues the products of more than 228manufacturers of high fidelity andsound equipment.

A new and enlarged SemiconductorProducts Booklet was announced re-cently to all Raytheon IndustrialTube Distributors. This new bookletcontains complete and up-to-date infor-mation on Raytheon Transistor andDiode characteristics.

John F. Rider Publisher, Inc., 116 W.14th Street, N.Y.C., has released a clear,practical, easy to understand book called"Resonant Circuits" by Dr. Alex Schure.This 72 page book is the 16th volume inthe Electronic Technology Series by thispublisher. It concerns itself with resis-tors, capacitors and inductors which arefound in various combinations of seriesand/or series parallel resonant circuits.Analyses are made for the elementscomprising each circuit and then thecircuit itself is analyzed. This book sellsfor $1.25.


RIDER SPEAKS

JOHN F. RIDER

WE recently made a trip to themiddle west and it was really

gratifying to note that many serviceorganizations believe there is merit inour suggestion that the service industryshould diversify.

We had occasion to talk to severalmen, strangely enough the largest op-erators among those to whom we spoke,and each one of them has diversified hisservice efforts. Yes, they do TV in-stallation and service, but in addition tothat they install and service auto radioreceivers. They buy the receivers fromthe manufacturer set distributor and dothe installation work. They servicewhatever hi-fi equipment becomes avail-able. The territory is not yet too hotfor hi-fi, but even so, they see this fieldas a source ol.f income, and every dollarof income counts.

In addition, tape recorders are serv-iced, as are record players and room airconditioners. The latter type of efforthas special significance because it helpstake up the summer slack, as far as TVis concerned. The midwest is a good airconditioning area because it sure canget hot in the summertime! Their eyesare also set an whatever industrial elec-tronic business can be developed.

All of this in the face of the fact thatthere is still television service work tobe done.

We had occasion to speak to anothergroup which is embarking upon anapprentice training program which itis trying to work out with one of thelocal schools. This training program,while starting with TV, will not neces-sarily be limited to TV. They are mind-ful of the fact that men must be trainedif there is going to be a supply of per-

sonnel for the servicing field in the faceof whatever attractions are being offeredto pull men out of the servicing field.

Another interesting item, at least tous, was that many people in the servic-

ing industry are not too brand conscious.Somehow or other, servicemen (wedon't know how many, but we do knowthat there are some) seem to feel thatthe brand means very little when theymake their selection of replacementparts. Of course, they are interested inprocuring parts which fit a need with-out any "gimmicking," but whetherthey buy one brand or another seems tomake no difference. It's simply a caseof what the jobber has to sell. If he hasbrand A they'll buy brand A, and if heChas brand B they'll buy brand B.Whether or not this situation prevailsall over the nation we don't know, butmaybe some parts manufacturers arefaced with the problem of selling brandsmore emphatically than in the past.Admittedly, some manufacturers havebeen doing this, but the impression isthat the program of selling a brandcould be strengthened to advantage.

One other item which wants moreattention than it seems to be getting isthe self -serviced tube checker. Thereare some who feel that this tube sellingplan is going to die. It does in somestores, then rears its head somewhereelse. We can't quarrel with the rightof people to sell tubes in this manner,but we do believe that those facets ofthe industry concerned with the sale oftubes to the public via service channelsand the service industry itself mightwell afford more serious considerationof this problem. There are places in the


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ELECTRONIC S1ERVICING JUNE, 1957al

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Distributor Has

ReplacementModules

for Servicing 1957 Auto RadiosPAC is a group of interconnected capacitors and resistors, combined ina single -insertion unit. Several popular 1957 model automobile and truckradios employ this new concept in component packaging. When servicingthese auto radios, a complete PAC (Pre Assembled Circuit) module canbe quickly and easily replaced.

Your ERIE Distributor has PAC Replacement Modules in stock.See him for complete information and prices.

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THE ANSWERMAN

Inquiries Sent To The Answerman Will Be Acknowledged Only

If Accompanied By Radio -TV Service Firm Letterheads.

by ELECTRONIC SERVICING Technical Staff

Dear Mr. Answerman:I have a Magnavox receiver in which

the picture is quite snowy. The RFamplifier tube has been checked andthe antenna is good. I tried another TVreceiver on the antenna and the substi-tution receiver worked fine. Also, in myshop the receiver exhibits the same con-dition of a snowy picture. The voltagesseem to be about normal and all othertubes that might contribute. to this con-dition have been substituted. Now, Idon't know what to do. What can yousuggest ?

H. P.Mineola, N. Y.

When the agc resistor feeding the pos-itive delay voltage to the tuner agc lineincreases in value the symptoms pro-duced are just as you have found, asnowy picture. It is suspected that R225,the 9.1 megohm resistor shown- in Fig.A has become higher in resistance andis thus the cause of this difficulty. Re-sistors which feed positive delay volt-ages in such circuits often increase invalue and cause this type of trouble.

330K

R2259.1

.22,5(1 MEG

270 V

/000

V2064/12 6A N8

A.G.C.KEYER

Fig. 1-An increase in the value ofR225 may cause excessive snow.

It is suggested that you replace the 9.1megohm resistor with one that has a5% tolerance. Magnavox supplies theresistor under part number 230094-254.

Mr. Answerman:I have a Dumont RA -170 that is giv-

ing me trouble. There is insufficientwidth, the picture being short 1Y2inches on each side. I have checked allthe components in the horizontal cir-cuit

J. C. D.Cheyenne, Wyo.

There are few components that cancause lack of width without a seriouschanging in any of the dc voltages.Several possibilities are immediately ap-parent. If C276, the cathode by-pass con-denser opens, degeneration will occurand reduce the input signal thus re-ducing the width. Shorted turns in thehorizontal size coil L214 will cause anarrow picture because of the absorp-tion of large amounts of energy. This


V220HON. OUT

6606

Fig. 2-Elements which may be re-sponsible for the loss of sweep.


TAXICAB COMMUNICATIONS

[from page 11]

generator commutator will prove to besatisfactory. Should such a capacitorprove ineffective, a generator filter canbe used which has more attentuation.These are available from many manu-facturers.

If the armature commutator is dirty,then there will be more than averagearcing at the brushes. If the generatorreceives irregular maintenance, it mightbe wise to by-pass the brushes with apair of high quality capacitors.

Regulator Suppression

Regulator suppression can be done ona "cut -and -try" basis. Generally speak-ing coaxial capacitors will be requiredon either the battery or the armature orboth. If these capacitors prove ineffec-tive, however, they should be removed.The field terminal of the regulator can-not be directly by-passed. To do sowould quickly burn up the points in theregulator. In addition an accidentalshort in the capacitor would remove allresistance from the generator field andperhaps cause very serious damage tothe generator. On a cut -and -try basisagain, however, a small resistor of aboutfour ohms in series with a .002 capacitorcan be tried. This should be mountedinside the regulator body if possible. Ifit proves ineffective, it should be re-moved. If all the above techniques fail,some thought might be given to theuse of shielded wires between the arma-ture and regulator.

Bonding

In general bonding material shouldbe as non -inductive as possible. Thisdictates the use of solid materials forconnections where possible. Whereflexibility is a definite considerationbraid will have to be used, although thishas more inductance than solid mate-rial might have. Generally speaking, itis necessary to have a good bond be-tween the fire wall, frame, and theengine. In many cases bonds from thehood to the fire wall on both sides ofthe car prove quite effective. A definitesource of noise on many cars is theinsulated tailpipe. Some sort of bond

on this tailpipe to the frame should beconsidered. There have also been re-ported cases where bonding the steeringcolumn to the frame produced excellentresults, and in at least one case a floatingbumper was proving to be quite a noisesource until bonded to the frame.

Static Noises

The static charge built up in tires,brake shoes, front wheels, fan belt, etc.require individual attention. Tires canbe treated with anti -static powder.Brake shoes can be grounded to theback-up lights. Another considerationfor bonding the exhaust pipe is heavilygraphited penetrating oil. The oilevaporates or burns off and leaves aconductive bond between the parts. Thishas been found to be more effective thangrounding straps in some cases as thestraps lose their effectiveness as oxida-tion continues. The graphite does notoxidize but stops oxidation at the pointsof contact. In bonding to eliminate staticdischarges between parts of a car, it isa good idea to make a generous use ofheavy star washers on both ends of boltsto provide good contact.

Other Possibilities

In searching for noise it might be agood idea to inspect the engine while itis running in a dark garage. Sparks canbe clearly seen under such conditionsand sources of arcing which generatenoise in the receiver can be eliminated.Some care should also be given to theproximity of wires, fluid tubes, and rodsto the ignition wiring, and if so indi-cated, such rods, tubes or wiring shouldbe separated from the ignition harnessby a greater distance. It has even beenfound that wet 'heater hoses runningclose to the ignition harness will pick upignition noise and radiate it into theantenna. Another technique which hasbeen reported to show good results isthe use of a series tuned trap runthrough the bundle of ignition wireswhere they come together. The resonanttrap is grounded to the motor block atboth ends and consists of an LC circuitresonant in the neighborhood of six or

seven megacycles. This trap is tuneable,and is tuned for minimum noise re-sponse.

It is sometimes a good idea to waitfor one or two thousand miles beforesuppressing or attempting to suppressa brand new vehicle. It is generallyfound that a car will prove to be lessnoisy after a two thousand mile break-in run because the body continuity hasbeen somewhat improved by the con-stant vibration along city streets. Thusthe suppression job is often simplified.

In most cases it will be unnecessary

to go through all the suppression tech-niques just described. Generally speak-ing, it will be enough to add resistorplugs, a distributor resistor, and a coaxcapacitor on the generator armature.With perhaps the addition of a coaxialcapacitor to the battery side of the igni-tion coil, the average car will be broughtto a satisfactory noise level. Where thisis not true, then the foregoing sugges-tions may prove helpful. Each hasproved to be the answer to a stubbornnoise problem that resists the simplifiedtreatment. I

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ANSWERMAN[from page 42]

may be tested by removal of one leadof the width coil from terminal one ofthe fly back transformer. A similar con-dition may exist in the horizontal line-arity coil L211 and fly back transformerT203. Shorted windings in these com-ponents would reduce width and notaffect the dc voltages radically. Unfor-tunately the latter two components arebest checked by substitution since ashort of several turns will not alter theresistance reading materially.

Dear Sir:I have run into a real problem I

have in my shop a Truetone 2D3770Aportable. After two minutes of operationthe bottom of the pix folds over and thetop of the pix stretches out. The picturealso starts to roll.

H. J. E.Waco, Texas.

From your description, the troubleappears to be in the vertical outputstage. The 12L6 is saturating and pro-ducing foldover. This is borne out byyour cathode current reading of the12L6, V106, which is caused by a low-ered grid bias. There are two reasons

that the grid bias may be lowered.These are, a leaky coupling condenser,or a gassy output tube, or both. Manyservice problems that lead up to a blankwall are caused by the combination ofproblems that may alone be very simple.There exists the possibility of your nothaving tried both components simul-taneously; that is the coupling conden-ser and the output tube. A furtherpossibility is that occasionally new tubesare defective. Try several output tubes,to be sure.

0139

.047

C/38.047

VERT.LIN.

V/06VER7: Our

I2L 6

R1382M

R/45I.5M B+

Fig. 3-Schematic shows the ele-ments which will cause vertical fold -

over.

TRANSISTOR THEORY[from page 3]

the effect is the same as if a positivecharge were present. Actually, therobbed electron is said to fall into thehole created by the substitution of theindium atom for a germanium atom.Thus, holes behave as if they were posi-tive charges.

Since the neighboring germaniumatom is robbed of an electron it canalso be pictured as being left with ahole. To fill this hole it robs anotherneighboring atom of one of its valenceelectrons, thereby creating another hole.This process is repeated throughout thesample of germanium and sets up achain of events whereby holes are pic-tured as moving outwardly from thesource of the disturbance. Since holesare equivalent to positive charges, ger-manium to which indium is added issaid to be "P" type germanium, P stand-ing for positive. In this case indiumis referred to as an "acceptor" type

material.Comparing the processes involved in

creating N and P type germanium, wemay summarize by stating that:

1-In N type germanium the donoris a pentavalent substance, such as ar-senic, and leaves a number of free nega-tive charges available for conduction.

2-In P type germanium the acceptoris a trivalent substance, such as indium,and leaves a number of holes or equiv-alent positive charges available forconduction. It should be kept in mindthat conduction here is still a flow ofelectrons. However, conduction in semi-conductors is more readily understoodif we adopt the concept of a hole beingequivalent to a charge equal in mass,and opposite in polarity, to that of anelectron. N and P type semiconductorsare the foundation units in the manu-Eacture of rectifiers and transistors.

[To be continued]


SELL SERVICEWITH EFFECTIVE ADVERTISING

PART 2

NWSPAPER advertising is probablythe best all-round medium avail-

able to the average service agency ordepartment, both from the number ofpeople reached and the cost of advertis-ing per person. By far the best adver-tisement we have ever used (and arestill using), is a "column," which atpresent appears once a week on Friday-a "fight" night-next to the stationlistings, which in our local paper is nextto the sports pages. It is entitled "TEL-EVISION TIPS," and in it is discussedalmost anything pertaining to the serv-icing of television receivers, strictly fromthe non -technical point of view. Itmakes an honest effort to save the cus-tomer money by giving "tips" as tominor adjustments the customer canmake himself, how to clean the safetyglass, how to identify certain types ofinterference sporadically seen on thescreen, the advantages of an outside an-tenna, etc.

There is, of course, a limit to whatthe customer can do for himself, so these"tips" are rewritten and repeated at ir-regular intervals, on the theory thatthere will have been many who havenot read the original, have forgotten,or have recently moved into the areaand subscribed to the newspaper. Inbetween, subjects of general interestare covered, but these "general interest"columns still are linked with televisionservice.

Newspaper advertising, good as it is,should be supplemented by other forms-and don't sell radio short! "Spot" an-nouncements, for example, are surpris-ingly low in cost, price being governedby the number you use and the lengthof the "spot." Many manufacturers oftelevision receivers furnish, free of

charge, spot announcements alreadywritten and timed, and if you sell aswell as service, use them. Some high-priced "brains" have turned out the copyand you can depend upon it-it's good.If yours is a service set-up only, andyou can't write your own copy, the ra-dio station will do it for you if you letthem know in a general way what it is

By M. E. WIRT

you wish to stress. Have them "pitch"your advertisement toward the femininelistener; it can and will result in moreservice calls.

Direct mail can be a most effectiveadvertising medium, yielding a returnof 2% to 10% in replies. If used cor-rectly and followed faithfully, it cando a very good job. However, in serv-ice we normally have nothing to selluntil the set breaks down. Then, andonly then, do we come into our own,and at that time the customer is nottoo interested in what we have to usein order to repair the set-just so that itis repaired. In service, therefore, wemust be doubly careful in making upour mailing list, to whom we will mailour cards, circulars, etc., and how fre-quently it will be done. Otherwise costcan exceed benefits. Keep an accuraterecord of returns on your direct mailingreturns; people do move, die, or dis-appear. The Post Office can help youkeep your mailing list current as to ad-dresses at a very small cost to you.

Tube manufacturers offer a wide va-riety of post cards, posters, signs, win-dow streamers, and door -knob hangersfor your use. Their cost is low-for in-stance, post cards, imprinted with yourname, will cost you only the postage oftwo cents, and they carry a hard-hitting,cartoon -illustrated message.

Closely associated with direct mail ad-vertising using post cards or form let-ters is the circular, or "throwaway," andthat is exactly what the average recipi-ent will do with it-unread. Envelopestuffers suffer the same fate. Theyhave their place in an all-out advertis-ing campaign to sell appliances, dresses,or flower seeds, but their value in sell-ing service is debatable. After all, it isnot the parts and tubes we will use inrepairing the set which we are anxiousto push, it is the service itself. So allour advertising should be done with onethought only-to implant your nameand your company's name so firmly inthe customer's mind that when his setdoes require service, his first reactionwill be to think of you.

And after you have repaired his set,think of you he will, one way or theother, good thoughts or bad. If youhave done a good job, then you are inline for the best of all possible formsof advertising, the hardest -hitting, low-est cost type imaginable-word-of-mouth advertising. It is so good it is

priceless. You can't buy it. But if youhave repaired the set properly, and madethe right impression in doing it, youhave hired an untiring salesman foryour service that won't cost you a dime.A customer whom you have pleased byreturning his set to operating condi-tion in a very short time, at a nominalcharge, will tell his neighbor - andyou've got another customer. Sinceyour original customer has "no axe to

grind," his advice is accepted withthanks, and when it is necessary for theneighbor to call for service, it's you theywill call. That type of advertising can'tbe beat, and it's worth a little extra ef-fort to earn. Don't be too rushed tospend the few extra minutes necessaryto clean the safety glass, make minoradjustments, touch up a scratch on thecabinet, or oil a squeaking caster. Thesmall, thoughtful things are what thewomen remember!

Advertising service is like anythingelse-you will benefit in direct propor-tion to what you put into it. It is anaxiom that you must spend money inorder to make money-and one of thebest ways to spend it for tangible re-turns is in advertising.

*STOP CALL BACKS by always using C -D "cUss" ® -the tubularthat has proven itself the champ in the service field. Theyout -perform any other replacement because they're the onlymolded tubular with built-in extras that insure call -back -free servicing. C -D "cuss" are made exclusively for theservice trade.SPECIAL! "CUB SERVICE KIT" in all -plastic dispenser. You payonly for the capacitors. Ask your distributor salesman toshow you the new C -D "CUB SERVICE KIT" or write for details

Cornell-Dubilier Electric Corporation, South Plainfield, N.J.stop callbacks... insist on

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A compilation of specific re-ceiver service repairs, "bugs,"chronic troubles, field circuitchanges, manufacturers' pro-duction revisions, etc. The com-pilation enables the service tech-nician to pinpoint what is wrongwith any given TV set and to cor-rect the fault in the shortest pos-sible time.

Video Speed Service Systems is guaranteed to simplify servicing allTV sets. Contains over 600 service items representing over 2500 of themost serviced TV models now in use. Over 25 different manufacturers'lines are covered.

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1

-100 V.

( A )

VERTICAL RETRACE BLANKING [from page 7]

-100 V.

(B)

CRT

BLANKINGVOLTAGE

Fig. 4-Modification for blanking.

full B plus would be applied to thecathode driving it so positive that theCRT would be cut off. If C158 shorts,placed at ground potential, removingall bias, thus giving full brightness withthe brightness control being ineffective.

The General Electric circuit of Fig.3 may cut the CRT off if capacitorC311 shorts or becomes leaky. The posi-tive voltage on the grid of V9 causesheavy plate current thus producing alarge voltage drop across R320, theplate load resistor. This lowers the firstanode voltage to about 10 volts so thatthe CRT is cut off.

If any of the coupling condensersopen, the results will vary. Returningagain to Fig. 1, if 0157 opens, theblanking pulses would not reach thecathode and retrace lines would appearon the screen. Should C158 open, the

IN .01 47K OUT( A ) >

( B ) 11014(7 I(.047 OUT

22 K

( C )IN OUT

IN .05

(D)15K

02 m01

1K

.05 OUT

02

Fig. 6-Typical wave shaping circuitsto obtain blanking pulses.

(A )

Vi L7:tGEBLANKING

'RI

(B)

B+

Fig. 5-A different modification.

voltage divider action will fail and thefull pulse will be applied to the cathodethrough C157. The excessive blankingvoltage may tend to shade the upperportion of the picture if the CRT comesout of cut off during the early portionof the vertical scan. This effect willalso occur as a result of a lengthenedtime constant in the wave shaping net-work.

Set Modification.

When modifying a set to accept a ver-tical blanking circuit, there are threefactors to be considered. These are:

1. Modification of the CRT circuitto accept the blanking pulse.

2. Selection of an appropriate shapingnetwork.

3. Selection of a pulse take off pointin the vertical circuit.

In order to modify the CRT circuitwe must observe which element is driv-en by the video signal. If the grid isthe driven element the blanking pulseshould be applied to the cathode cir-cuit. Figs. 4A and 5A show two basiccathode circuits and Figs. 4B and 5Bshow the corresponding modifications.

The shaping networks used vary

CRT CRT

BLANK-ING

(A) ( B )

Fig. 7-Modification to allow injectionof pulse into grid circuit.


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CRT CRT

B+

(A) ( B )

Fig. 8-Modification when brightnesscontrol is in grid circuit.

from a two component circuit to com-plex arrangements. For purposes ofmodification, the simpler the waveshaping circuit is, the easier the taskbecomes. Fig. 6 presents four typicalwave shaping circuits. Of the four, Fig.6A has generally been found satisfac-tory for most sets. Use may be made ofthe printed circuit employed in theAdmiral 19T1 shown in Fig. 2C. TheAdmiral part number is 63CG-5.

If the grid circuit is to receive theblanking pulse, it is the one which mustbe modified. When the grid is ground-ed it may be changed as shown in Figs.7A and 7B and if it is used as thebrightness control circuit it may bemodified as shown in Figs. 8A and8B.

B+ B+

Fig. 9 - Take -off points for securingblanking pulses.

Pulse Take -Off Points

The pulse to be shaped and appliedto the CRT may be taken from severalpoints in the vertical circuit. A typicalvertical circuit is shown in Fig. 9. Thetake -off points are lettered from A toD. Points A and B may be used forcontrol grid blanking. When using thepulse from point A it is not necessaryto use a shaping network since we al-ready have the desired negative pulse.

In circuits using auto transformeroutputs such as those of Figs. 1 and 2C,the pulse polarity may be reversed byrelocation of the B plus feed thus giv-ing us three possible take off points; theplate or high side of the transformer,the bottom or the center point.

RIDER SPEAKS

nation where the method has taken abeating, but there are many places in thenation where it is still very much alive.Just what will b done to overcome itsselling features on Saturday night andSunday, the times when service shopsare closed, we don't know. Maybe noth-ing can be done to overcome the avail-ability of self-service at these times, butcertainly, every effort to acquaint thepublic with the availability of self-

service in service shops during the othersix days a week is warranted. The super-market may not be as big a problemas the drugstore because the supermar-ket is closed Sundays. Nevertheless, wehave learned of chains of 100 or 150stores which have contracted for self-service tube checkers. Supermarket op-erators are not foolish people. By andlarge their marketing practices are theresult of investigation. They are notgoing to waste any space. They arehandling a greater variety of productsthan ever before, and they can, without

[from page 41]

too much difficulty, persuade the house-wife to bring in a bag full of tubes fortesting. The whole thing is too big tobe sloughed off.

In connection with self-service tubechecking in service shops we would liketo express one word of caution. Thepublic should be given the opportunityto check tubes in a service shop withoutany aid on the part of the service tech-nician. The shop owner or his peopleshould stay as far away as possible fromJohn Q. Citizen while he is checkinghis own tubes. The atmosphere of thetube checking in service shop by thepublic should be exactly the same as inthe drugstore or supermarket. Make ita "Do -It -Yourself" deal throughout.This may not be possible with the con-ventional types of tube checkers whichmost service shops have, in which eventfire must be fought with fire; the serviceshop owner is faced with the problemof getting the self-service type of tubechecker for use by the public.

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POWER AMPLIFIERS IN HI-FI[from page 15]

now be discussed, together with an ex-planation of what the measurements aredesigned to show.

Test Equipment Required for Servicing

The essential equipment you will re-quire for servicing includes:1. A good audio generator having a

low impedance output, flat frequencyresponse from at least 20 cycles to20 kc and harmonic distortion of lessthan 1% at all frequencies. Thegenerator should also be equippedwith a variable attenuator, but thisneed not be calibrated accurately.

2. An oscilloscope having a vertical sen-sitivity of at least 0.05 volts per inchand good frequency response withinthe audio range.

3. An ac VTVM with the lowest fullscale range of .03 volts or less andgood frequency response within theaudio range.

4. Calibrated wirewound resistors (ofat least 50 watt rating) of 4, 8 and 16

resistorsused, if you have an accurate ohm-meter with which to set the taps.

5. Your regular VTVM.In addition to the above, a completely

equipped audio service center shouldinclude the following:6. An audio wattmeter, calibrated di-

rectly in watts and having its ownload resistors.

7. A distortion analyzer, either har-monic or intermodulation type. (Thelatter is by far easier to use and ispreferred.)

Shielded Cable

AUDIO GENERATOR

A -C

VTVM

AMPLIFIER

UNDER TEST

DUMMY/ LOAD RESISTOR

.,_THESE ITEMS MAY BE COMBIN-ED IN A DIRECT -READING

AUDIO WATTMETER

Fig. 2 - Setup to measure thesensitivity of an amplifier.

8. A square wave generator (used onlyon rare occasions).

Measuring Amplifier Sensitivity

The sensitivity of an amplifier is de-fined as the voltage input necessary todrive that amplifier to full output. Ithas nothing whatever to do with thepower rating of an amplifier. Thus, a10 watt and a 50 watt amplifier mayeach have sensitivities of 1 volt. Thatis, one volt input will drive either am-plifier to its full rated output. Thisspecification is easily checked by apply-ing the signal voltage required at theinput (with all level controls fullyclockwise) and measuring the wattageoutput with your audio wattmeter. (Inthe absence of this instrument, an acVTVM and a proper load resistor maybe used, together with the formula W= E2/R, where W is in watts, E is inac volts and R is the load resistance.)The setup is shown in Fig. 2.

Power Response

Power response, the ability of an am-plifier to produce uniform output at allfrequencies, can be measured with thesame set-up as that used to measuresensitivity. Set the audio input voltageat 1000 cycles to provide maximumpower (the actual power rating of theamplifier). Vary the frequency of signalthroughout the audio range-from 20to 20,000 cycles and note any deviationfrom the initial reading. The statementthat an amplifier has uniform powerresponse from 20 to 20,000 cycles within1 db means that at no time should themeter reading depart from the initialreading by more than 1 db either posi-tive or negative. It should be noted thatin power considerations, a change ofthree decibels corresponds to a changeof two to one in power. Thus, a tenwatt amplifier which is "down onlythree db" at 30 cycles is one which canproduce only 5 watts at thirty cycles.This is usually somewhat of a surpriseto the unsuspecting customer, who hasbeen led to believe by optimistic speci-fications that "3 decibels" is practicallyinaudible.

[To be continued]

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Aerovox Corporation 33

American TV & Radio Cc. 34

Amphenol Electronics Corp. 1

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Blonder Tongue Laboratories 36

Bussmann Manufacturing Co 3, 38

Clarostat Manufacturing Co. Inc. 11

Cornell-Dubilier Elec. Corp.

45, Cover 2

Duotone Company, Inc. 47

Electro Products Labs, Inc. 8

Electro-Voice, Inc. 15

Erie Resistor Corp. 42

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Heath Company 41

International Crystal Mfg. Co. 40

JFD Manufacturing Co., Inc. 48

Jensen Industries, Inc. 48

Jerrold Electronics Corp. 12

Mallory, P. R. & Co. Inc. 9

North American Philips Co., Inc. 35

Perma-Power Company 47

Philco Corporation 7

Pyramid Electric Company 13

Quietrole Company 48

RCA Batteries Cover 4

RCA Service Company 39

RCA Speakers 47

Radiart Corporation Cover 2

Raytheon Mfg. Co. 5

Roney Plaza 42

Service Instruments Corp. 48

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