SYLVANIA NEWS JANUARY 1959 VOL. 26, NO. 1 R. A. Humphreys, Technical Editor This information in Sylvania News is furnished without as LIFE TESTING OF TUBES IN TELEVISION RECEIVERS- cPartn> Under Part I, we discussed the test conditions and procedures used to life test the various television re- ceivers. Analysis of set survival data indicated a marked reduction in tube failures. Now let's consider how tube failure rates vary among TV sets made by different manufacturers. VARIATIONS IN SET SURVIVAL This question is quite vividly answered by the curves in Figure 1. Shown here are the expected set survival curves for two generally similar sets made by different manu- facturers. These curves are consistent with the curves of other years for the same manufacturers and, therefore, are not peculiar to a certain year. It should be noted here that design of some manufacturer's sets have im- proved while others have taken the opposite course. In the past few years, the number of 600 -milliampere series -heater re- ceivers has equaled and exceeded the number of transformer -powered receivers. By analyzing the series - heater set failures and computing the expected set survival for each of the past three years, the curves shown in Figure 2 were obtained. It would seem from these curves that there has been no improvement in tubes in the past three years, as was suggested previously. However, when the same curve was constructed for trans- former -powered receivers, a different Sylvania News result was obtained. As shown in Figure 3, a four -to -one improvement in expected set survival has resulted in the last three years. The curves shown for the transformer -powered receivers reveal that controls on heater specifications brought on by the series -heater sets have also con- tributed to improved set survival in transformer -powered receivers. REDUCTION IN FAILURE CAUSES To assist the factories in improving tube survival, tube failures were grouped according to frequency of causes. A list of the most frequent causes is given in Table I. From this table it is seen of the four major failure causes, percent failures have been reduced by a factor of three to one, on the average. As of 1957, the big offender is a collection of mis- cellaneous items of which there are some 22. Another informative table is found in Table II. This table shows those applications with the highest fre- quency of failures. Because of the severe requirements placed on these tubes, over 65 percent of all tube failures fell in one of these four *Based on a paper authored by E. H. Boden, Advanced Applications Engineer, Receiving Tube Operations. J > 5 cc co 1- W co z W U cr W a 100 80 40 20 0000C000000000090000000000,° Qo00f.,00000000000 \ °° 0 °° 0000000...0000C,° \ GOOD DESIGN °o° O o00 \ \ - _ POOR \ DESIGN 0 2 4 6 8 10 12 14 16 HOURS OF LIFE (HUNDREDS) Figure 1-Computed set survival of sets manufactured. January 1959 5
Transcript
SYLVANIA NEWS
JANUARY 1959 VOL. 26, NO. 1R. A. Humphreys, Technical EditorThis information in Sylvania News is furnished without as
LIFE TESTING OF TUBES INTELEVISION RECEIVERS- cPartn>
Under Part I, we discussed the testconditions and procedures used tolife test the various television re-ceivers. Analysis of set survival dataindicated a marked reduction in tubefailures. Now let's consider howtube failure rates vary among TV setsmade by different manufacturers.
VARIATIONS IN SET SURVIVAL
This question is quite vividlyanswered by the curves in Figure 1.Shown here are the expected setsurvival curves for two generallysimilar sets made by different manu-facturers. These curves are consistentwith the curves of other years for thesame manufacturers and, therefore,are not peculiar to a certain year. Itshould be noted here that design ofsome manufacturer's sets have im-proved while others have taken theopposite course.
In the past few years, the numberof 600 -milliampere series -heater re-ceivers has equaled and exceededthe number of transformer -poweredreceivers. By analyzing the series -heater set failures and computing theexpected set survival for each of thepast three years, the curves shown inFigure 2 were obtained. It wouldseem from these curves that there hasbeen no improvement in tubes in thepast three years, as was suggestedpreviously. However, when the samecurve was constructed for trans-former -powered receivers, a different
Sylvania News
result was obtained. As shown inFigure 3, a four -to -one improvementin expected set survival has resultedin the last three years. The curvesshown for the transformer -poweredreceivers reveal that controls onheater specifications brought on bythe series -heater sets have also con-tributed to improved set survival intransformer -powered receivers.REDUCTION IN FAILURE CAUSESTo assist the factories in improvingtube survival, tube failures weregrouped according to frequency ofcauses. A list of the most frequentcauses is given in Table I. From thistable it is seen of the four major
failure causes, percent failures havebeen reduced by a factor of three toone, on the average. As of 1957, thebig offender is a collection of mis-cellaneous items of which there aresome 22.
Another informative table is foundin Table II. This table shows thoseapplications with the highest fre-quency of failures. Because of thesevere requirements placed on thesetubes, over 65 percent of all tubefailures fell in one of these four
*Based on a paper authored by E. H. Boden,Advanced Applications Engineer, ReceivingTube Operations.
J>5cc
co
1-Wco
zWUcrWa
100
80
40
20
0000C000000000090000000000,°Qo00f.,00000000000
\°°0
°° 0000000...0000C,°\ GOOD DESIGN °o°
O o00
\\
- _POOR \DESIGN
0 2 4 6 8 10 12 14 16
HOURS OF LIFE (HUNDREDS)
Figure 1-Computed set survival of sets manufactured.
Table II-Percent failures of the tubes tested in the circuits listed at the acceleratedlife condition of high line voltage.
applications. However, in spite ofthe high percentage of failures inthese applications, a significant im-provement in tube survival has beenachieved in all four applications.
It should be noted that the per-centages listed in the precedingtables represent tube failures underthe described accelerated conditionsand should not be construed to meanthat an equal percentage of fieldfailures will occur. As was pointedout previously, the accelerated lifeconditions are necessary to obtainthe maximum information in a mini-mum of time.
VHF VERSUS VHF -UHF RECEIVERS
At Emporium, Pennsylvania, thereare two experimental satellite tele-vision stations in operation onChannels 22 and 82. This makesEmporium particularly well suitedfor the comparison of expected setsurvival of VHF sets and VHF -UHFsets. As part of the life -test program,a UHF receiver must be capableof satisfactorily receiving off -the -airsignals on both Channels 22 and 82.To eliminate as many variables aspossible, only VHF -UHF receiverswere used for this comparison.
Expected set survival curves forVHF receivers and VHF -UHF re-ceivers, which include data represent-ing failures of the UHF oscillatortubes, were plotted as shown inFigure 4. According to the corn-
100
80
60
40
20
puted curves, at the completion of1500 hours there would be 1.2 lessreceivers surviving because of UHF.Therefore, although there is anadditional tube in a UHF receiver,the expected set survival at 1500hours (one year of operation) is notsignificantly degraded by the additionof UHF.
While conducting the above men-tioned life tests in the VHF -UHFsets, the failure rates of the varioustypes of tuner tubes were carefullytabulated. This data, as shown inFigure 5, substantiates the conjecturethat since the UHF oscillator tubehas had a "habit of hiding" in someremote corner of the TV chassis, ithas not been uncommon to replacethis tube, when the chassis is removedfrom the cabinet for a particularservice call, as a Preventive Mainte-
xxxx+x
kxa x*44.4.x
x
- x,r
xxxxxxxxYYxxx1954 255 xxxxxxxxxxx1956=57
1955 56 _xXx
0 2 4 6 8 10 12 14 16
HOURS OF LIFE (HUNDREDS)Figure 2 -Percent set survival of series -parallel heater string TV sets complemented
with Sy vania tubes.100
80
60
40
20
XxMxxxxxKxxxXXxxxxXkxy\,\\
4kxxxxY.y-kxcX
\ xxxxxxxxx !1956 -'S7
\ 1955-56 xxx
kkXxxyixxxxxxxxA7(XxxX4,...\ \ \`\\\ , ,
1954255
---.-
2 4 6 8 10
HOURS OF LIFE (HUNDREDS)12 14 16
Figure 3-Percent set survival of transformer powered TV sets complemented withSylvania tubes.
6 January 1959 Sylvania News
loo
80
60
40
20
UHF FAILURES IN
LESS UHF FAILURE
LUDED
0 200 400 600 800 1000
TIME IN HOURS
200 1400 1600
Figure 4-Computed set survival of VHF and VHF -UHF receivers at the acceleratedlife condition of high line voltage.
167.
10%
142
///
/./.1///' /
2*/
PENTODE/
UHF //
///://
// AFigure 5-Percent failures of tuner tubes tested at accelerated life conditions.
Sylvania News January 1959
nance measure to preclude a "call-back" at some future date.
CONCLUSIONS
The facts presented above illustratethe extraordinary pains that Sylvaniahas taken to gather factual data ontheir product and how it performsunder actual field conditions.
Moreover, Sylvania's improvedtube performance has brought abouta significant increase in set survivalover the past few years. For furtherimprovement in set survival, im-proved tube survival will need to besupported not only by improved setdesign, but by more enlighteningservicing techniques.
It is hoped that the informationsupplied here will bring about therealization that deterioration of othercomponents in a TV set, over a periodof time, can create such adverseoperating conditions that even thebest tube manufactured will fail in ashort length of time.
YOUR
SERVICE HINTS
WANTEDAttention-Service Dealer readers ofSYLVANIA NEWS! What has hap-pened to the Service Hints columnover the past year? This column,which is supported by YOU, shouldinclude all technical hints believeduseful to your fellow Service Dealer.
For each hint accepted, you willreceive a certificate worth $10.00that can be applied against any ofthe many items listed in Sylvania'sAdvertising -Merchandising AidsBooklet. These items include: tools,tube caddies, technical manuals,display signs and etc. If you are notfamiliar with this booklet, pick up acopy at your Sylvania Distributor orwrite to our Central AdvertisingDistribution Department, 1100 MainStreet, Buffalo 9, New York.
Perhaps you are not quite sure justwhat comprises a Service Hint. Itshould be nothing more than a simplemethod or device used to solve irri-tating or time-consuming serviceproblems. It could be that you havedevised a simple but unique method
7
Your Service Hints Wanted(Continued from page 7)
for servicing a remote section of achassis without removing it from thecabinet; maybe you've solved anelectrical problem peculiar to aparticular chassis -such as a remotecomponent being responsible for thedifficulty encountered in the sectionbeing serviced.
Any service hint which you feelmight be of value to you and yourfellow service dealer should be mailedto Sylvania Electric Products Inc.,Receiving Tube Operations, in careof the Technical Publications Sectionlocated in Emporium, Pennsylvania.
Sylvania is not obligated to returnany material submitted for publica-tion, whether or not published.
SERVICE HINTSTHIRD HAND
Most of us who do a good bit ofservicing wish occasionally we hadthe use of a third hand. This can bearranged by simply wrapping arubber band around the nose of long -nose pliers. The rubber band servesto clamp the pliers to the component,leaving both hands free to completethe necessary repair.
JOHN E. SEKERAKErie, Pennsylvania
PCB HOLE CLEANERTo the list of semi -special toolsappearing in the recent article"Printed Circuit Service Hints", youmight add the common ordinarywooden toothpick. Wetting thetoothpick in cold water and insertingit in a hole filled with molten solderresults in a nice cool clean hole.
TV TOMAstoria, N. Y.
NOTICE TO TECHMANUAL SUBSCRIBERS
The great response to Sylvania's11th edition technical manual hasforced us to print record numbersof it. The presses are rolling nowand delivery of your new 11thedition will be made during thelatter part of February.
8
SUPPLEMENTARY TUBE TESTER SETTINGS
Listed below are important additions to the roll charts for Sylvaniatube tester models 139, 140, 219, 220, and 620. Make sure yourcharts are completely accurate and up-to-date by adding theseimportant facts, now.
FOR TUBE TESTER MODELS 139 AND 140TYPE A B C D E F G TEST1J3 1.4 0 2457 0 8 69 V2EN5 2.0 0 - 0 1 41 -r
In the course of servicing radio andtelevision receivers, the servicemanhas familiarized himself with variouskinds of frequency conversioncircuits. We might say that ingeneral, there are three basic typesof frequency conversion circuits.Oscillator -diode such as is found inUHF -TV tuners and converters;oscillator -triode (pentode) such asis found in VHF -TV and FM tuners;and the pentagrid converter which ismost generally found in radio -receivers.
Early in the 1930's, both thepentagrid and autodyne converterswere developed. At that time, dueto the fact that the autodyne circuithad a higher gain than the pentagridcircuit, the autodyne was morewidely used than its counterpart.Later, however, when automaticvolume control was developed, theautodyne dropped from the scenesince the application of AVC voltageonly produced "motorboating," orloss of oscillation.
Recently, the autodyne has begunto make a return and is currentlybeing employed in a number of AMreceivers. Two of the factors con-tributing to the return of the auto -
Sylvania News
dyne are: (1) With the addition ofa diode and a circuit modification,the conversion gain may be changedby the application of AVC voltage;and (2) A change in the listeninghabits of the Public in general. Mosthousewives today are content tolisten to the local broadcast station;thus receivers are currently beingmanufactured with little or no AVC.
HOW IT WORKS
An autodyne converter is simply aself -oscillating mixer. That is, all ofthe elements involved in the generat-ing of the local oscillator signal alsotake part in the mixing action, andvice versa. One basic form of theautodyne is shown in Figure 1. Thereceived signal is selected by the
tuned circuit (L1, CI) in the inputtransformer Ti and impressed on thecontrol grid of the triode. The triodeoscillates at a frequency determinedby the tuned circuit (L2, C2) in thetransformer T2. As a result ofthe large oscillator voltage and thereceived signal voltage being com-bined between the cathode and thegrid, the plate circuit produces asignal current which is the receivedsignal converted to a frequency equalto the difference between the receivedsignal frequency and the frequencyat which the triode is oscillating. Thiswe call the IF frequency. The IFsignal is then coupled out of thecircuit by means of transformer T3which, in turn, delivers the signal tothe first IF amplifier stage for furtheramplification.
TRIODE MIXER
To better understand how it happensthat the desired difference signal is
produced in such a simple circuit, itwould be advantageous for us toreview the theory of a simple triodemixer and then a triode oscillator.Following this we will see how thesame triode may be made to performboth functions at the same time, asis done by the autodyne circuit.
Let us consider a triode which hasimpressed on its grid two signals.One, a very large signal produced bya local oscillator, and the other, asmall signal which is the received orincoming signal. The local oscillatorsignal, being large, will cause theplate current to fluctuate betweenzero and maximum plate current asshown in Figure 2. Likewise, thetransconductance will vary from zeroto maximum Gm. As a result of themagnitude of the oscillator drive, theplate current and transconductancebecome a series of pulses. The ampli-tude of these pulses is modulated bythe incoming signal.
As a result of this modulation,the plate of the mixer produces notonly pulses at the local oscillatorfrequency rate and the resultantharmonics, but also side bands aboveand below the local oscillator signalcurrent and each of its harmonics.Of particular interest to us is thelower side -band which is at afrequency equal to the differencebetween the local oscillator and thesignal frequency. This is betterknown to us as the IF frequency.This component of the plate currentis coupled out of the circuit by asuitable tuned circuit and thenamplified in the next stage.
TRIODE OSCILLATOR
Now let us examine a triode oscillatorcircuit. Here we see the triode work-ing as an amplifier with its outputcoupled back to its input. This feed-back circuit is tuned to a frequencywhich establishes the proper phaserelation between the input and outputof the amplifier. As a result of theoscillations becoming larger andlarger each time they are fed backand re -amplified, the grid -cathodeswing becomes correspondinglylarger. After a few oscillations wesee that the tube is at maximum gainpart of the time and at zero gain partof the time. The average gain is thensome point between zero and maxi-
mum determined by the developedgrid -cathode bias. The developedgrid -cathode bias is thus a self-limiting voltage developed by theoscillator action. At this point, thetriode is operating as described bythe curve in Figure 3.
The reader should now notice thesimilarity between the curves inFigure 2 and 3. All that is lackingin the oscillator to make it a mixeris an incoming signal. Therefore, asignal may be coupled into the grid -cathode circuit as is done in Figure 1to, in effect, modulate the developedoscillator bias. Then, as before, theplate circuit will have a signal currentat the difference frequency. Thisdifference signal is coupled out ofthe plate circuit by means of an IFtransformer as in Figure 1.
AUTODYNE AND AVC
It was stated earlier that AVC couldnot be applied to an autodyne con-verter. The reason for this is thatwhen a tube is working as an oscil-lator, it is performing two functions-amplification and limiting. Limit-ing, you will recall, is accomplishedby self -biasing. If a DC voltage(AVC) is applied to reduce the gainof the amplifier, the tube automati-cally reduces the self -biasing voltageby the amount of the DC bias andthe gain remains the same. However,as the DC bias increases and becomeslarger than the amount of self -bias,the circuit begins to "motorboat."Larger DC bias shuts the tube offcompletely.
To overcome this difficulty, de-signers have added a diode to thecircuit as shown in Figure 4. In thecircuit the triode has only onefunction - amplification, and thediode performs the limiting action.The secondary of the oscillator tankhas two outputs with respect toground. One, the feedback signalto the amplifier input (cathode), andthe other, the diode limiting circuit.Limiting, in this case, is accomplishedby loading and not by developing biasvoltage. For example, as the oscilla-tion increases, the diode currentincreases which increases the load onthe secondary of the oscillator tank.This, in turn, decreases the couplingbetween the primary and secondaryof the oscillator tank and, therefore,
6 February 1959 Sylvania News
Figure 4. Autodyne Converter with Diode to make possible use of AVC.
L
/
B+
G . OSCILLATOR GRID
G3= SIGNAL GRID
Figure 5. Typical Pentagrid Converter Circuit.
the amount of signal fed back tothe cathode.
ADVANTAGES OF THE AUTODYNE
The most outstanding advantage ofthe autodyne converter is its highergain. This can be readily demon-strated by comparing the autodynecircuit in Figure 1 to a commonpentagrid converter circuit as shown
Sylvania News
in Figure 5. Note that in the penta-grid circuit the tube is required tohave two control grids, grids No. 1and 3, plus another grid, grid No. 2,working as an anode. To performthe function of an oscillator, theanode grid must intercept a consider-able part of the cathode current. Ifthe reader observes the ratio of plateto cathode current for the Type
February 1959
6BE6, which appears in most TubeManuals, he will see that only 1/ orapproximately 25% of the cathodecurrent reaches the plate. This meansthat the conversion gain of a Type6BE6 when used in a pentagrid typecircuit is only 25% of the conversiongain obtained with a Type 6AU6 inan autodyne circuit.
Now, returning to Figure 1, we seethat almost all of the cathode currentis plate current. Actually, somecathode current goes to the gridbecause of oscillator action. Oscil-lator feedback and the incomingsignal are both inserted between thegrid and cathode.
In comparing the circuits in Figure1 and 5, the reader has perhaps notedthe circuitry is somewhat reduced andthat the tube requirements are less.Thus, circuit simplicity becomes asecond advantage of the autodynecircuit.
A third advantage makes the firsttwo all the nicer. That is, the highergain and reduced circuitry areobtained without reduced image re-jection or increased oscillator pullor noise.
ERRATUMPicture Tube
Characteristics BookletThe basing diagram 8JK, forTypes 17DAP4, 21EAP4, and24AVP4 is incorrectly drawnin the recently issued PictureTube Characteristics BookletRevision No. 1, 1958. Insteadof showing Pin No. 6 connectedto Grid No. 1, the correctbasing diagram for these types,as shown below, should havePin No. 6 connected to GridNo. 2 and be so labeled.
G4 CL G3 Gs
7
SYLVANIA RADIO CHASSIS1-629-1, 2
Figure 6 is a partial circuit diagramof the Sylvania Model 629 radiochassis. After a brief study, we seethat V1 (Type 12AU6) is being usedin an autodyne converter not toodifferent from the circuit in Figure 1.Although a pentode tube is used, it istriode connected as far as the oscil-lator frequency is concerned. At theIF frequency, the tube is working asa pentode with the effective plateresistance being increased by thefeedback to the screen grid.
Since the 12AU6 is an oscillatoras well as a mixer, it is necessary tomake sure the signal input circuit isfree of oscillator voltage. This pre-vents radiation of the signal atoscillator frequency through the re-ceiver antenna. The capacitor C7(4.7 µµf) is, therefore, connectedbetween the control grid and the IFoutput transformer tap. This capaci-tor neutralizes any oscillator voltagethat might be present at the grid as aresult of the tubes interelectrodecapacitive network.
CONCLUSION
In the foregoing discussion, welimited ourselves to AM receivers.However, it should be noted that theAutodyne may be used at any fre-quency at which a triode may bemade to oscillate. Also, the methodof modulation (television or FM)places no restriction on its use.
In the early days of UHF tele-vision, a single tube autodyneconverter was used to receive signalsfrom Sylvania's experimental stationKG2XDU on Channel 22. Thecircuit for this one tube converter isshown in Figure 7. In this circuit,the input frequency and the oscillatorfrequency are so close to one anotherthat one less tuned circuit is needed.
Figure 6. Partial Circuit Diagram of Sylvania Radio Chassis 1-629-1, 2.
-41
TO
ANTENNA
8+80V
300 OHMOUTPUT (CHANNEL 3)
TO TV SET
4.7µµf
6T4
MOM II& WNW
R FC
Figure 7. Autodyne UHF -TV Converter.
READER'S SERVICE HINT DRILL SLEEVEThe sudden lurch inward, experi-enced when drilling holes in chassis,can cause extensive damage to com-ponent parts. This can be prevented
by using a drill -sleeve approximately1/2 inch shorter than the drill itself.
Copper and/or brass tubing ofvarious sizes, generally used for this
purpose, is available from hobby aswell as electrical supply houses.
JOHN H. WILLIAMSPomano Beach, Florida
8 February 1959 Sylvania News
SYLVANIA NEWS
MARCH 1959 VOL. 26, NO. 3R. A. Humphreys, Technical EditorThis information in Sylvania News is furnished without as
"PICTURE ON THE WALL" TELEVISION(Part 1.)
by R. M. Bowie,Vice President, Sylvania Research Laboratories, Bayside, New York
The "Sylvatron," which is a devicecombining the principles of theelectroluminescent lamp and thevariation in electrical conductivity ofphotoconductive materials, has fre-quently been suggested as the basisfor "picture on the wall" televisiondisplay. The purpose of this articleis to describe several approaches tothis objective, to point out someproblems involved, and to describeprogress toward. realization.
An essential part of this form oftelevision display is the phenomenonof electroluminescence, in whichcertain kinds of phosphor powders,when subjected to a varying electricfield, extract energy from the fieldand transform it into light. Insimplest form the lamp, shownschematically in Figure 1, is com-prised of a glass plate which has atransparent, conductive inside sur-face. This surface is coated with athin layer of insulating materialwhich has embedded in it a smallamount of electroluminescent phos-phor. The insulating material ordielectric is backed by anotherconductor which may be a metal foil.
Electroluminescent lamps currentlyon the market look much like sheetsof steel coated with porcelain enamel.Such lamps when operated at 110volts, 60 cycles, generally exhibit abrightness which after 40,000 hoursof operation is only 35 per cent lessthan the initial value.
Sylvania News
When a lamp like the one justdescribed, is operated at an alternat-ing potential of several hundred volts,brightness curves can be obtainedsuch as those in Figure 2. Thesecurves indicate that the brightnessincreases with frequency within therange covered. Actually there is alimit set to the increase in brightnesswith frequency by the capacitance ofthe lamp and the resistance of thetransparent conducting film. Thislimit is determined largely by con-struction and/or size and, with smalllamp sizes, can reach several mega-cycles. Figure 2 also shows the wayin which brightness increases withvoltage; maximum voltage is limited,of course, by electrical breakdown.The practical brightness obtainedwith such a lamp is currently limitedby dielectric breakdown to a valueconsiderably below the instantaneousbrightness now attainable by thescanning spot on a picture tube.
In the light -producing process,some of the power consumed is trans-
formed into heat. For this reasonthe efficiency currently obtained islow, being normally about 2 lumens/watt, although an efficiency of 10lumens/watt has been obtained. Forcomparison, a 100 -watt incandescentlamp has an efficiency of 16 lumens/watt.
The present low efficiency andhigh capacitance introduce two otherproblems that must be surmountedin the eventual design for commercialtelevision display. The efficiencyinfluences the driving power requiredand thus the resulting heating of thedisplay panel, while capacitance tendsto load the driving circuits.
ELECTROLUMINESCENTTELEVISION DISPLAY
Let us now turn our attention totelevision. To display the intendedpicture one must scan, synchronizeand modulate. To these three fund-amental problems must be addedthat of obtaining high brightness
.......o.......e..... . .. ... e.... ......
-METAL FOIL_ -PHOSPHOR EMBEDDED
IN DIELECTRIC--TRANSPARENT CONDUCTIVE
COATINGGLASS
Figure 1-Cross section of the basic EL lamp.
March 19595
100
90 -
80 -
70 -
60
50 -
40 r-
30 -
20 -
lo
o
2000 CPS
1000 CPS
400 CPS
120 CPS
60 CPS
0 100 200 300 400 500 600
VOLTS Figure 2-Brightness as a function of voltage.
T00
PROJECTION TUBE
LENS
IMAGECONVERTER
Figure 3-Television display systemutilizing a small projection tube and an EL image converter
6 March 1959
levels without excessive persistenceof image.
One system of displaying thepicture is to use an image converteror intensifier and a small projectiontube, as depicted in Figure 3. Theimage converter is an electro -luminescent lamp combined with aphotoconductor, as shown in Figure4. It comprises, first, a sheet ofglass rendered conductive on the sidenext to the electroluminescent layer.An almost opaque, non -conductinglayer between the electroluminescentlayer and the photoconductor pre-vents optical feedback. Finally, avery fine wire mesh serves as theother electrode.
The image converter may be con-sidered as broken up into elementalareas, though actually the surface isunbroken. Each such elementalarea can be pictured as a small elec-troluminescent area in series with aphotoconductive area. The equiv-alent electrical circuit shown inFigure 5 illustrates this point andshows how the resistive component(R1) of the photoconductive areascontrols the light output from theelectroluminescent lamp section.Since the value of R 1 varies accordingto the intensity of the input illumina-tion, the resistive component of eachelemental photoconductive area canbe thought of as a potentiometer.In darkness it may assume a value ofseveral thousand ohms or more.When excited by a bright light itsohmic value will approach zero. Atypical curve in terms of photocon-ductor current is shown in Figure 6.
Referring again to Figure 5, theeffectiveness of R1 in controllinglight output from the electrolumin-escent lamp is limited by shuntcapacitances C1 and C2. Even if theresistance of R1 were to go to infinityin the dark, a portion of the ac supplyvoltage would be on the lamp due tothe reactance of capacitance C1. Ifthe photoconductive layer and theelectroluminescent layer were ofabout the same thickness and di-electric constant, then in the darkapproximately half the voltage wouldbe across each layer. Here thenon-linear nature of the electro -luminescent lamp response can be adistinct boon, as it may be used to
Sylvania News
° °°o°°° oo°°°°° °°o°°°° ° e°°
°°
xxxxxxxxxxxxX xxxx xx x xxx°.Gi i' // ; % ii /// /// ,%' /7/ //% //' /%/
FINE WIRE MESH
_ -PHOTOCONDUCTOR- -OPAQUE LAYER
- -EL PHOSPHOR-CONDUCTIVE COATING-GLASS
Figure 4-Cross section of the image converter.
*R1
AC SUPPLY
I I
I I
I
L J J
PHOTOCONDUCTOR EL LAMP
JIMAGE CONVERTER
* VALUE OF RESISTANCE RI VARIES ACCORDING TO INTENSITYOF LIGHT STRIKING PHOTOCONDUCTIVE LAYER
Figure 5-Schematic representation of the image converter.
reduce the brightness of the phosphorunder conditions of no input illu-mination. At zero input illuminationthe voltage across the electrolumin-escent layer would drop to only abouthalf of maximum, but the light woulddecrease by a factor of 5 or so. Underfull input illumination, of course,the resistance of the photoconductordrops almost to zero and nearly fullsupply voltage appears across theelectroluminescent layer. By propercompounding of the photoconductorand proper choice of input illumina-tion level, the time constant can bereduced to below a tenth of a second,permitting the showing of motionpictures.
Sylvania News
o 10E. 0.9
= 0.6
07u 0.6ó 0.5
'5' 0.4
0.3
IS' 0.2
2 3 4 5 6 7 8 9 10 II 12
BRIGHTNESS, FOOT -LAMBERTS(EL LAMP AT 400 C.P.S.)
Figure 6-Photoconductor currentversus brightness.
March 1959
SERVICEHINTS
PHILCO MODEL 51-T1836
This set would exhibit severe syncpulling and picture bending on strongsignals only. Reducing the contrastcontrol would reduce the amount ofpicture distortion or removal of oneside of the antenna would result in astable picture. This problem wasisolated to filter condenser C303Awhich filters the B + to the 12AV7,first sync separator. Replacementof filter resulted in normal pictureoperation regardless of signalstrength.
Leonard D. ChiomaWinter Park, Florida
KNOB SPRINGS
How many times have you lost aknob spring and went scurryingaround to find one with little success?
Here is a solution. You will findthe iron core laminations of dis-carded output transformers, whencut down to the correct size, willmake excellant springs or wedgesfor any type of knob.
William C. BermanBrooklyn, New York
TEMPORARY PLATE CAPREPAIR
On a recent house -call while re-moving the plate cap of thehorizontal output tube, the wirebroke loose from the cap as a resultof heat and crystallization. A tem-porary field repair was accomplishedby winding a paper clip around anail, forming a spring. Upon slip-ping the spring over the tube cap,the lead going to the horizontaloutput transformer was placed be-tween one of the coils of the spring.A wrapping of plastic tape completedthe repair until a replacement capwas obtained from the shop.
Don HopkinsBury, Que., Canada
7
SUPPLEMENTARY TUBE TESTER SETTINGSListed below are important additions to the roll charts for Sylvaniatube tester models 139 and 140. Make sure your charts are completely
accurate and up-to-date by adding these important facts now.
FOR TUBE TESTER MODELS 139 AND 140TYPE A B C D E F G TEST1DN5 1.4 2 48 4 1 016 49 T
NOTE: The tube types noted are of the auto hybrid types. To test them, the conversionoutlined on page 8 of the October issue of SYLVANIA NEWS must be made.
8 March 1959 Sylvania News
SYLVANIA NEWS
APRIL 1959 VOL. 26, NO. 4R. A. Humphreys, Technical EditorThis information in Sylvania News is furnished without as
"PICTURE ON THE WALL"( Part I I )
TELEVISION
by R. M. Bowie, Vice President, Sylvania Research Laboratories, Bayside, New York
Under Part I, we discussed how theprojection television tube shown inFigure 1 and the image convertershown in Figure 2 fulfills the firstthree criteria for displaying a picture;namely scanning, synchronizationand modulation. They do not,however, satisfy the commercial re-quirements for television with respectto brightness and cost.
Unlike the motion -picture projec-tor, only one picture element is fullyilluminated at a time. Since thereare some 180,000 picture elements,each one must be very much brighterthan the apparent picture brightness.Were there no phosphorescent decayof the projection tube screen and nolag in the photoconductor response,a picture element in the highlightswould have to achieve 180,000 timesthe highlight brightness of thepicture. Actually, the decay and thelag reduce this number appreciably,but probably not enough to comewithin the brightness range of electro -luminescent materials commerciallyavailable.
One remedy appears to bethe use of optical feedback from theelectroluminescent layer to the photo-conductor. Just as electrical feedbackis used to sustain oscillationin vacuum tube circuits, sufficientoptical feedback will keep the lamplighted once it has been turned on.To prevent the feedback light fromspreading to adjacent areas we breakthe lamp into discrete, small areas as
Sylvania News
shown in Figure 3. The photocon-ductive layer is deposited on the sidesof very small glass pillars positionedon top of the electroluminescentlayer. When light falling on a pillarlights the elemental lamp beneath it,the feedback light is restricted almostentirely to going up the same pillar.Hence, only that pillar remains brightand spreading is prevented. In thisplaque, each element goes on fullywhen triggered by outside light andremains on until the whole plaque isturned off. Each element is thereforebi-stable. It will remain either off or
on until transferred to the other state.The system currently has in it all of
the elements of a projection systemand in addition an electroluminescentimage intensifier with its powersupply. Because space behind thescreen must be made available forthe projection equipment, thereappears to be no saving possible inthe size of the cabinet.
COMMUTATOR SYSTEMA more attractive package wouldresult if the projection tube werereplaced by a flat device capable ofbeing scanned, synchronized and
Figure 1-Television display system utilizing a smallprojection tube and an EL image converter.
April 19595
__-METAL FOIL-PHOSPHOR EMBEDDED
IN DIELECTRIC--TRANSPARENT CONDUCTIVEl
COATINGGLASS
Figure 2-Cross section of the image converter.
Figure 3-Cross section of the mosaic EL panel.
L
DOT RATE PICTURECOMMUTATOR INFORMATION
0 00
oO 0o oo oo oO 1 0O 1
O 1
I
J\THE X -Y PANEL
MODULATOR
DC
SUPPLY
o
LINE RATECOMMUTATOR
6
Figure 4-Commutator system for TV using EL display panel.
April 1959
modulated to drive the image in-tensifier.
If one starts with an electrolumi-nescent lamp and, in effect, slices theback conductor into strips runningone way and the transparent con-ductor into strips running the other,he would have a cross -grid panel. InFigure 4. the panel is fed by twocommutators which, for standardtelevision, would probably be elec-tronic. After the line -rate com-mutator has designated a line, thedot - rate commutator successivelyselects the dots along the line. Aseach is selected, a surge of voltage isapplied and then removed, producinga bright spot at the intersection of theselected strips. Unfortunately, theunwanted portions of each strip arelighted sufficiently to form a notice-able "cross" when the panel is viewedin dim surroundings. This is becausethe selected horizontal strip is pulsedpositively and the selected verticalstrip is pulsed negatively; hence halfvoltage appears at all other pointsalong the selected strips. This crosseffect is, of course, less apparentunder brighter viewing conditions.It can also be suppressed by externalcircuitry or by incorporating rectifiersinto the panel.
We have thus achieved a scanningsystem and, presumably, synchroni-zation. To achieve modulation onecan modulate the voltage made avail-able to the commutators taking intoaccount, of course, the highly non-linear brightness characteristic of thephosphor already mentioned.
ERRATUMThe Basing Diagram 9CV, for theType 6BQ5, 8BQ5 is incorrectlyshown in the recently issued Receiv-ing Tube Characteristics Booklet,Revision No. 2, 1958. The correctBasing Diagram for the 6BQ5, 8BQ5is shown below.
9CV
Sylvania News
SYLVANIA NEWS
SECTION7).
TELEVISION TUNER APPLICATIONS OF
IMPEDANCE DIODESI.OWby William F. Palmer and Donald H. Rice, Semiconductor
Engineering Laboratory, Sylvania Electric Products Inc.
JUNE 1959
VOL. 26, NO. 6
O>
6.9
ó
R. A. HUMPHREYS, TECHNICAL EDITOR This information in Sylvania News is furnished without assuming any obligations.
The use of germanium very -low -impedance diodes as voltage sensitivecapacitors is becoming popular inoriginal equipment tuners of new tele-vision sets. In this article, you willfind data concerning the variation ofdiode capacitance with bias voltage,discussion of circuit requirements forresonant circuits tuned with variablecapacitance diodes, practical circuitsfor television fine tuning, FM auto-matic frequency control, and tele-vision automatic frequency control.
XL Inductive ReactanceAFC Automatic Frequency ControlFíf Intermediate FrequencyFlo Local Oscillator FrequencyFsig Signal FrequencyA Sensitivity Without FeedbackA' Sensitivity With FeedbackB Sensitivity of Feedback Net-
workUHF Ultra High FrequenciesVHF Very High Frequenciest Time Constantpf Pica Farad
JUNCTION CAPACITANCE
A semiconductor diode, when biasedin the reverse direction, acts as acapacitance shunted by a resistance.For a step junction, the shunt resist-ance is usually constant (saturated)and high over a considerable voltagerange.
Junction capacitance varies inverse-ly with the square root of the appliedvoltage. And, with a constant biasvoltage, junction capacitance will berelatively insensitive to temperaturechanges because the effects of changesof resistivity and mobility with tem-perature tend to cancel. Voltagetunable LC and RC circuits mayeasily be constructed using a junctiondevice in conjunction with externalresistance or inductance. SylvaniaVLI type "point contact" diodes, to
June 1959
a close approximation, act as stepjunctions.
Fig. 1 shows a typical curve ofjunction capacitance and diode termi-nal capacitance as a function ofreverse bias voltage for a VLI diode.These data were taken on a Boontontype 250A RX meter at 1.0 Mcs.
CIRCUIT CONSIDERATIONSFrequency Control Sensitivity of
Diode -Tuned Circuits
When a reverse -biased diode is usedin conjunction with an inductor (referFig. 2), a voltage tunable resonantcircuit results. An expression forfrequency sensitivity (frequencychange per unit voltage change) maybe derived and is shown below:
S
F F 1
V 4V 1 + Cd/Ccwhere :
S = frequency sensitivityF = frequency
AF = change of frequencypV = change of voltageCd = diode capacitanceCc = coupling capacitanceV = bias voltage
From the above it can be seen thatmaximum sensitivity is obtainedwhen (Cd/Cc) is small, F is high, andV is low. Cc is usually used forcoupling only and therefore may bemuch larger than Cd. Large valuesof Cc may be undesirable in certain
5
Fig. 1-Capacitance as a Function of BiasVoltage for a D1114 Diode.
circuits since they may lead to un-desirably high self -bias voltages.(This is discussed in greater detailbelow.)
CIRCUIT QFrom the definition of Q for aresonant circuit, a variable capaci-tance diode Q may be defined asshown below. (A reverse biaseddiode is assumed.)
At high frequencies, the diode Qis determined mainly by the diodeseries losses. At low frequencies, Qis determined mainly by diode shuntlosses.
If a lossy inductor is assumed tobe in parallel with the diode, theexpression QHF now becomes:
1QHF = 2wfCR (2)
Where:R is the sum of diode series re-
sistance and the inductor seriesresistance, C, is diode capacitance.
A graph of typical values of highfrequency Q as a function of diodereverse bias voltage for D1114 andD1156 (VLI type) diodes in parallelwith various inductances is given inFig. 3. The peak a -c voltage acrossthe diode was 0.22 volt so that at lowbias voltages large signal and ulti-mately forward bias conditions exist.Resonant frequencies using the idealinductances indicated are also shownat various bias voltages along thecurves, thus indicating possible tun-
} Bml
Cd C6
.-,
ec.W n<a (C..CdY
si _1
e0 "a6Cd -u
H-o .,V
sie a- (C.,et)Í
Fig. 2-Sensitivity of the Voltage TunableOscillator.
ing ranges. Large signal Q valueswere calculated from measured valuesof capacitance and average values ofshunt a -c resistance for the diodes.
DIODE BIASINGDuring small signal conditions (peaka -c voltage across the diode much lessthan d -c bias voltage,) the diode d -cbias voltage effectively determinesdiode capacitance. If the diode iscoupled to an inductance, the fre-quency characteristics of the resultingcircuit are controlled by the diodebias. However, since the diode is arectifier and may be coupled to apower source (see Fig. 2) by Cc there
Fig. 3-Graph of Circuit Q for D1114 andD1156 Diode as a Function of Bias Volts.
may be a rectified d -c (reverse) self -bias voltage across the diode. Thereare, therefore, two basic methods forobtaining diode bias voltage; self -biasand externally applied bias (combina-tions of these are also possible).
SELF -BIAS OPERATION
If no external bias is applied, it canbe seen that diode voltage will varyapproximately between zero andsomewhat less than the peak to peakvalue (see Fig. 4). Under these con-ditions, diode capacitance will be-come instantaneously very large asthe voltage approaches zero. Duringthe upper half of the cycle diodecapacitance is smaller than at themidpoint of the cycle and of littleconsequence when compared to thevalues obtained during the lower halfof the cycle. As a result, there is waveshape distortion and the effectivecapacitance is large; larger thanwould be predicted from the average(d -c) voltage reading on a meter.For example, line b in Fig. 4 is thed -c meter reading, but line f isactually the frequency (fundamental)
determining voltage and is usually10% to 20% less than the biasvoltage (line b).
EXTERNAL BIAS OPERATIONWhen the diode bias voltage issupplied from an external source andsmall signal conditions prevail, theeffective diode capacitance is de -
Fig. 4-Waveform of Diode Voltage forSelf -Bias Operation.
termined by the d -c bias voltage asthe sum of package and junctioncapacitances. Under these conditions(analogous to class A operation ofvacuum tubes) there is little or nowave shape distortion.
The bias supply should be fairlywell regulated and the voltage shouldnot be greater than needed for thedesired capacitance variations. Un-necessarily high reverse voltages maycause excessive leakage currentswhich would easily vary with temper-ature. This would cause capacitancevariations by voltage divider action.
When large signal conditions pre-vail, however, the effective diodecapacitance again becomes anoma-lously large as in the self -bias case.This leads to a third method ofoperation.
COMBINATION OF SELF ANDEXTERNAL BIAS OPERATIONS
In the limit of this case, as diode volt-age approaches zero during part ofthe cycle, the wave form approachesthat of Fig. 4. In less extreme cases,however, substantial distortion maystill exist depending upon the ratio ofpeak a -c swing to d -c bias voltage.
TELEVISION FINE TUNINGThe frequency of a television localoscillator may be controlled using a
6 June 1959 Sylvania News
VLI variable capacitance diode. Fig.5 shows the basic circuit used, andFig. 6 shows the plots of local oscil-lator frequency as a function ofdiode bias voltage for channels 2 and13. From these curves it can be seenthat a 2% frequency deviation iseasily obtained. At higher biasvoltages the diode capacitance isapproximately 0.5 pf, the value ofpackage capacitance. The slopes ofthese curves at any operating (bias)point will give the control sensitivityin cycles per volt. From the curvesof Fig. 6, it can be seen that sensi-tivity increases as bias voltage de-creases and increases as frequencyincreases.
FM AUTOMATIC FREQUENCYCONTROL
When the diode bias control voltageis supplied from the output of afrequency discriminator, automaticfrequency control (AFC) may easilybe achieved. It should be remem-bered, however, for proper AFCaction the diode bias control voltageshould effect the circuit degener-atively. The necessary conditionsfor AFC in a typical FM tuner usinga variable capacitance diode are thata degenerative closed loop be formedconsisting of the local oscillator,
+8
Fig. 5-Basic Circuit for TV Local Oscil-lator Fine Frequency Control.
mixer and i -f amplifier, frequencydiscriminator and detector, and vari-able capacitance diode. Such acircuit has been constructed andtested using a conventional FM tunerand a VLI variable capacitance diode.Fig. 7 shows the circuit diagram.DC output from the Foster -Seeleydiscriminator -detector is applied tothe diode at b. Fig. 8A showsthe discriminator -detector character-istics. Fig. 8B shows a plot of localoscillator frequency as a function of
Sylvania News
diode reverse bias voltage.From Fig. 8A it can be seen that
an increase in local oscillator fre-quency (Fif = Flo - Fsig) causesthe discriminator output to becomemore positive, and vice versa. Underthese conditions, if the diode wereconnected directly to the discrimina-tor output, a regenerative circuitwould result and there would be noproper AFC action. It should alsobe pointed out that as the discrimi-
Fig. 6-Local Oscillator Frequency vsDiode Bias for Channels 2 and 13.
nator voltage changed polarity thediode bias would change from reverseto forward, thus seriously loweringthe oscillator Q. (If the outputpolarity is correct, however, thediode may in some cases be directly
Fig. 7-AFC Circuit for FM Tunerconnected to the discriminator.
Because of this, the circuit shownin Fig. 7 was developed. In this casethere are other methods for securingdegenerative AFC action such asreversing the discriminator output, ortuning the local oscillator below thesignal frequency (sub -heterodyne) sothat Fif = Fsig - Flo.
A fixed positive diode voltage isapplied between point a and ground.Therefore, the total voltage acrossthe diode (Vab) is the fixed biasvoltage minus the discriminator out-put voltage.
The fixed bias voltage may be
June 1959
conveniently obtained from one ofthe tube cathode bias voltages, avoltage divider and reference dioderegulator across the power supply, asmall battery, or from diode self -biasvoltage. Va must be fairly wellregulated since it determines theoperating point and thus the sensi-tivity of the circuit. The degree ofregulation, however, need not be highsince any variations would be reducedby the degenerative feedback.
Overall circuit sensitivity dependsupon the i -f amplifier -discriminatorsensitivity (expressed in volts/kcs)and the oscillator -AFC diode sensi-tivity (expressed in kcs/volt). Theamplifier -discriminator sensitivity isobtained from the slope of the curvein Fig. 8A. The oscillator -AFC diodesensitivity is obtained from the slopeof the curve in Fig. 8B at the operat-ing point (Va.)
The sensitivity of a feedbacksystem may be defined as the fre-quency change produced by a stresson the system when no feedback ispresent divided by the change pro-duced by the same stress with feed-back present.
Using the analogy of an amplifierfeedback this becomes:
A' - A1 +BA(degenerative feedback) where:A = sensitivity with no feedbackA' = sensitivity with feedbackB = sensitivity of the feedback net-
workThen:
AA, = 1 -I-- BA _ dF (4)
From Fig. 8A, A has a value of0.06 volt per kc, and from 9b at 0.05volt bias, B has a value of 1000 kcsper volt. Therefore, over all sensi-tivity (1 + BA) = 61. This meansthat a 61 kcs drift for an uncontrolledlocal oscilator would be reduced to1 kc with feedback present. Thisvalue is greater than that oftenobtained with vacuum tube reactioncircuits.
The circuit time constant (t) de-termines the time lag between theinitial correcting voltage change andthe actual frequency correction.Since the AFC loop is integral withthe audio output, t should be long
(3)
7
0
_2
-s --10-_12_
1
10.7 10.9
r,l (mc,)
2.
110.6
110,4
110.2
110
o .
1098
10960 1 2 3 4
Diode Reverse Rios Volmge
Fig. 8A-Discriminator Output Charac-teristics.
enough so that AFC correction doesnot follow the lowest audio fre-quency. In this circuit shown t =(R1 + R2) C1, and is approximately0.032 sec. This corresponds to afrequency of approximately 30 cps.
Using a well regulated supply forVa, it was noted that a negligible localoscillator drift occurred over a periodof 51/2 hours of tuner operation. Thisincluded warm-up time and periodi-cally moving the hand close to theexposed local oscillator tank whilethe tuner was tuned to a local FMstation. Oscillator drift was de-termined by observing the d -c dis-criminator output voltage change.Fig. 9 shows a point by point plot ofthe d -c discriminator output voltagewith and without AFC action as i -ffrequency was varied.
Using similar techniques televisionAFC may be obtained. AFC voltagewould be obtained from a discrimina-tor at the video i -f output.
FACTORS AFFECTING THE CHOICEOF DIODE COUPLING CAPACITOR
In the two cases discussed above,where the diode is used to tune anoscillator, the amount of energycoupled to the diode is determinedmainly by the size of Cc with respectto (Cc + Cd). (Refer to Fig. 2).
It is therefore often desirable to usea small value of Cc so that diodeself -bias is kept small. Low self -biasvoltages mean greater sensitivities.
(AV
is large-see Fig. 6), losses are
reduced (less forward conductiontime per cycle,) and the range of
8
Fig. 8B-Local Oscillator Frequency asa Function of Diode Reverse Bias.
diode bias control voltages changesneeded is reduced. On the otherhand, changes of Cd with bias havetheir greatest effect upon the circuitwhen Cc is very large. It is apparent,therefore, that an optimum value ofCc exists with respect to Cd. Itshould be pointed out that for lowoscillator amplitudes, the self -biasvoltage will be small regardless of thesize of Cc so that a large value of Ccmay be tolerated, giving maximumsensitivity. It is advisable, therefore,to judiciously choose the value of Ccwith respect to (Cc + Cd), oscillatoramplitude, sensitivity required, andbias control voltage range available.
Fig. 9-Graph of Discriminator OutputCharacteristics With and Without AFC.
OTHER APPLICATIONS
Only two practical applications havebeen discussed in detail. It should bepointed out that other variable capac-itance diode types may be used astuning controls at other frequencies.In general, variable capacitancediodes may be used in almost allapplications involving variable capac-itors. Some specific examples arelisted here :
June 1959
1. Remote television fine tuning2. Receiver tuning (ganged stages)3. Dielectric amplifiers (adjustable
filters)4. Other feedback control systems5. Wave shaping and compensat-
ing circuits (e.g., sawtooth line-arity control)
6. Variable phase shifting anddelay networks
7. Frequency modulatorsAutomatic frequency control may
be obtained using circuits other thanthe common Foster -Seeley discrimi-nator and difference detector. Forexample, the Round -Travis discrimi-nator or the ratio detector may beused. It is also worth noting that avery simple frequency sensitive de-tector may be obtained by detectingon the "slope" of a tuned circuit.The fact that this circuit does nothave a linear frequency responsecharacteristic is not of prime im-portance as long as AFC only isrequired. Two examples of thiscircuit are shown in Fig. 10. In eachcase LC is tuned slightly above orbelow Fif. DC output is proportionalto frequency.
Fig. 10-Simple Frequency Detectors
ADDITIONAL INFORMATION ONFILAMENT VOLTAGE TEST UNIT
FOR HIGH VOLTAGERECTIFIERS
The Weston Model 301 Meter usedin the "Filament Voltage Test Unit forHigh Voltage Rectifiers," SylvaniaNews, March 1958, is not a catalogueitem. This thermocouple type metermust be ordered directly from Westonspecifying a heavy cobalt magnet andan eight (8) ohm coil movement. Theend product would be a 450-500 maModel 301 meter.
The Type 17 Vacuum Thermocouple,used in conjunction with the aboveunit, is available from the AmericanThermo -Electric Company located at7269 Santa Monica Blvd., Los Angeles46, California.
Sylvania News
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Figure 2-To better serve the serviceman or home -builder, the above Nomographemploys scales which may be increased or decreased by any factor of 10 provided both
scales remain identical.
Actually, since both scales are identi-cal, it doesn't matter which scale isused to read the value of parallelresistance.
Should a circumstance arise wherethree or more resistances are to beparalleled, a process of eliminationshould be used. First solve for twoof the three values and then using theresultant and remaining value solvefor the answer. Thus, the Nomo-graph can be used to solve for the
6
resultant of any number of paralleledresistors.
The Nomograph would no doubtsee more use in a case where a specificresistance must be used and theserviceman or experimenter justhappens to be fresh out of that par-ticular value. Now, by using as afulcrum, the point on the 45° linedirectly above the resistance needed,any combination of resistors notedat each end of the straight -edge could
July - August 1959
be paralleled and used.For the convenience of the
serviceman or home -builder we haveincluded a ready -to -use Nomographin Figure 2. It is drawn to representstandard graph paper and the identi-cal scales range from 1 to 1000.Depending on the particular valuesof resistance needed, the scales maybe increased or decreased by anymultiple of 10 provided both scalesremain identical.
Sylvania News
SCREEN DISSIPATION - Important Factor in
Horizontal Deflection Tube LifeSylvania's Engineering Departmentmaintains a close and continuoussurveillance of its tubes in servicein the field. One interesting problemencountered, which required specialattention, was that of early lifefailures peculiar to replacement hori-zontal amplifier tubes.
Conclusive investigations, con-ducted with the aid of SylvaniaService -Dealers throughout thenation, revealed that variations incircuit components during life wereresponsible for the majority of earlylife failures in replacement tubes. Inthese cases, electrical tests conductedon tubes exhibiting short life incustomers sets, indicated low emis-sion or low peak plate current. Oncethis was established, a mechanicalanalysis (breaking the tube open)would indicate an excessive screendissipation type of failure.
Let's now consider the operatingconditions that can cause excessivescreen dissipation. The screen grid,of course, is required to dissipateelectrical energy in the form of heat.It, as well as other tube elements, isdesigned to operate within a specifieddissipation rating. However, opera-tion of the screen grid above its
maximum rating causes the gridlaterals to reach a temperature muchhigher than intended which, in turn,causes minute particles to be drivenoff and deposited on other elementsincluding the cathode. This in effect,"poisons" the cathode; causing itsemission properties to gradually de-cay. When this deterioration occurs,the TV set in question starts to exhibitshort scan, low brightness and poorfocus.
The question that now comes tomind is what caused the tubes tooperate at such excessively highscreen dissipation levels in the firstplace. In many instances, the culprithas been found to be the series screendropping resistor changing in valuewith life. For example, a decreasein the value of the screen griddropping resistor of the horizontaldeflection amplifier will tend to in-crease the screen grid voltage anddissipation. In sets which do notuse a screen dropping resistor, im-proper adjustment of the WidthControl may produce the sameconditions.
Depending upon exact conditions,defective components, sometimes
further aggravated by high linevoltage and improper set adjustmenttend to accelerate increased electrodedissipation, resulting in early lifefailures. These conditions may influ-ence the life of tubes and componentsof other circuits. That is, an increasein screen voltage of the horizontaldeflection amplifier due to a defectivescreen grid resistor may increase theboost voltage. This, in turn, increasesthe electrode voltage, current anddissipations of other circuits, such asthe vertical deflection system, whichalso derives B supply from thissource. Unfortunately, if a service -dealer is not fully aware of thisparticular situation he may simplyreplace the tube without getting tothe source of the trouble.
In conclusion, if normal tube lifeand a minimum of call-backs isdesired, the changes in the values ofcomponents with life and the disas-trous results this can produce mustbe carefully considered by the servicetechnician. A check of the value ofthe screen dropping resistor and thescreen dissipation with the replace-ment tube in the socket, may insureagainst a call-back in a few weeks.
SERVICE HINTS"BIFILAR IF COILS"
Recently, we had occasion to observean unusual defect in a 1951 RaytheonTV receiver having the circuitcommon to Models C-1401 andM-1402-3-4.
The customer's complaint was thatboth sound and picture had gonedead. He had himself replaced ablown fuse in the low voltage supply.A fuse of the proper 0.25 amp. ratingmelted as soon as the set was turnedon. He tried a 0.5 amp. fuse withthe result that the 5U4G rectifierburnt out.
Examination in the shop with aVTVM revealed that, where theservice data called for 35,000 ohmsbetween the filament of the 5U4Gand the chassis, only 180 ohmsexisted. A further check showedthat, equipped with a new rectifier,the power supply, including all thehigh -capacity filters, was in workingcondition. Various by-pass capaci-tors that might be defective were
Sylvania News
tested, but none were found to havea serious leakage resistance. Therather baffling question, then, inan apparently simple problem was :What was causing a reading of 180ohms everywhere in the main B+circuit beyond the 0.25 amp. fuse?
The answer lay in a 25-mc. bifilarcoil, coupling a 6AU6 fourth videoIF amplifier to the video detector.As is known, primary and secondarywindings on this type of coil are close -wound together to produce over -coupling and double -hump response.The insulation between primary andsecondary in the defective com-ponent had broken down allowingthe full output of the power supplyto be fed through a 5600 ohm platedecoupling resistor to ground. Withexcessive voltage across it, the re-sistor decreased in value to 180 ohms;no doubt when the set owner insertedthe 0.5 amp. fuse. Necessary replace-ments were made and the receiverrestored to operation.
It was observed that with a 5600ohm decoupler the voltage applied
July - August 1959
to the plate of the 6AU6 was con-siderably above the 300 volt maxi-mum rating of the tube. This perhapsaccounted for the eventual break-down of the IF coil due to theelectrical pressure between primaryand secondary being greater thanthe resistance of the winding insula-tion. The plate decoupling resistorwas replaced with a 15,000 ohm1 -watt unit, which brought the platevoltage within the recommendedmaximum.
An open RF or IF coil due to awinding that has melted or broken asa result of excessive operating volt-ages, thermal expansion and con-traction, or electrolysis, is common.A shorted coil, producing thedescribed effect, is apt to take us bysurprise unless we remember thepeculiar construction of bifilar com-ponents. The experience gained inthe instant case can be used to ad-vantage on nearly any make of TVreceiver.
William RittenourHuntington, West Virginia
7
SUPPLEMENTARY TUBE TESTER SETTINGSListed below are important additions to the roll charts for Sylvania Tube TesterModels 137, 139, 140, 219, 220 and 620. Make sure your charts are completely
accurate and up-to-date by adding these important facts now.
MODELS 137-139-140TUBE TESTER SETTINGS
TYPE
12DT5
A
12.6
BCD4 56 19
E
5
F G
013Z 9
K
712.6 4 35 19 5 016Z 9 7
TYPE A BCD E F G TEST 12DV7 12.6 4 159 37 5 7T 6 8
R. A. HUMPHREYS, TECHNICAL EDITOR This information in Sylvania News is furnished without assuming any obligations.
A THIRD CHANNEL FOR STEREOby
W. J. Sember, Receiving Tube Operations
The past eighteen months have seena phenomenal growth in sales ofstereophonic sound systems for usein the home. From the early systems,which were in most cases developedmerely by adding a second channel toalready existing Hi -Fi equipment,new and better methods of stereoreproduction have been developedThese newer methods have takenstereophonic sound out of thenovelty class, and placed it in theposition of realistic and excitinghome entertainment; and the mainte-nance of these home entertainmentcenters should enhance the businessof any serviceman.
EARLY STEREO SYSTEMS
Much has been learned of the truenature of stereo reproduction in therelatively short time since equipmentbecame widely available. It was firstthought that to produce stereo sound,all that was needed was two separatesound channels. Thus, the equip-ment manufacturer provided the twochannels; but in many cases thisequipment was not balanced inter-nally, either in stages of gain or inquality of the speakers in the twochannels. It was later learned thatalong with providing two channels ofstereo, it was desirable to providethese two channels with no phasedifference so as not to cause a loss ofthe true stereo effect. A system withunequal stages in the two channels,where, for example, one channel has
Sylvania News
an even number of stages, and theother channel has an odd number ofstages, may display an undesirablephase difference between the twochannels. In a system such as this,if the speaker separation is too greator if speaker phasing has not beenused to correct for the overall phasedifference, a "hole in the middle" orloss of the stereo effect will occur inthe area between the speakers.
THREE-DIMENSIONAL EFFECT
On many of the early stereo demon-strator records, a phase difference ofthis type was not critical, since mostof these attempted to emphasize this"ping-pong" effect or sound fromtwo sources. Demonstrator recordsof a bowling ball rolling down analley and a railroad train going bywere nice to listen to once, but thenovelty of living in a bowling alley ornext to a railroad track was bound towear off. Even some early musicalrecords in stereo showed only a littleimprovement over regular Hi -Fi.Critical manufacturers began to ex-plore the possibilities of true, three-dimensional stereo, rather than stereofor directional effects only. That is,stereophonic reproduction whichproduces a "curtain of sound" infront of the listener; sound which hasdepth and realism, rather than justright and left.
In studying this true stereo effect,it soon became obvious that phasingof the program material was perhaps
September 1959
the most critical factor in producingthis effect. It was also learned thatthe stereo records did not always endup with the same phase relationshipin which they started, and thatrecordings from different manufac-turers differed in phase relationshipsbetween the two channels; both ofwhich may cause loss of the truestereo effect. It became obvious thata method had to be devised to re-produce stereo sound such that achange of phase in the two channelsdid not cause this loss.
THIRD CHANNEL PRODUCESA "CURTAIN OF SOUND"
While these improvements were beingdevised in stereo reproduction, agreat stride was made in stereorecording methods. While earlierstereo recordings were cut withdirectional microphones as shown inFigure 1 to give directionality to thesound, it was soon learned that moreof the true stereo effect could becaptured if the method of recordingshown in Figure 2 was used. Threeor more non -directional microphonesare used to provide the two channelsof stereo. Each microphone "hears"all the sound from the orchestra, butwith different levels from differentdirections. The third or "center"channel is blended into the two out-side channels by the recording engi-neer to provide the two separatesignals for the stereo cutter.
It is obvious that the quality of the
5
STEREO CUTTER OR TAPE HEAD
Figure 1-Early method of stereo recording.
ORCHESTRA
NON -DIRECTIONAL
MICROPHONES
STEREO CUTTER OR TAPE HEAD
Figure 2-Later method of stereo recording.
stereo recording is influenced to agreat extent by the skill of the record-ing engineer; but the immediate resultof the use of this method of recordingwas that the overall quality of stereo-phonic recordings improved greatly.The music on these records seemedto have more "body"; and the stereosystem produced the desired "curtainof sound" in front of the listener.The listener could still "place" indi-vidual instruments, but the soundwas blended so he could hear themnaturally, with both ears. Thus, thedirectional effect was still present, butit was obtained by having unequallevels coming from two speakers,
6
rather than by having all the soundfrom one side of the orchestra comingfrom one speaker. This sound wasinterlaced in the area between thespeakers to provide an overall regionof sound rather than sound from theright and sound from the left.Speaker position becomes less im-portant, since it matters little to theaverage listener whether the violinsare on the left or the right, so long asthe overall "curtain of sound" ispresent.
The quality of sound from theolder equipment was greatly im-proved by these newer stereo records;but as the stereo material improved,there was also the drive to improveon stereo reproduction. It was de-termined that frequencies below 300cycles contributed little to the overallstereo effect. At these low frequen-cies, the wavelengths of the soundwaves are so long that the distancebetween the ears is not an appreciablepart of a wavelength, so the head doesnot mask the sound between the ears.Since it is difficult to determine direc-tivity at these low frequencies, theycontribute very little to the overallstereo effect.
RECENT STEREO DEVELOPMENTS
This principle is utilized in the newequipment shown in Figures 3 and4. Separate low, mid and high -
frequency speakers are used in theamplifier to provide an effective thirdchannel. The "woofers" from bothchannels are housed in the mainconsole, while the mid and highrange speakers from the two channelsare housed in the "wings" or exten-
LEFT
CHANNEL
RIGHT
CHANNEL
Figure 3-Output circuits of "3 -dimensional" stereo amplifier.
September 1959 Sylvania News
MAIN CONSOLE
WOOFERS
(BOTH CHANNELS)
EJ.
LEFT CHANNELTWEETER AND MID -RANGE
RIGHT CHANNEL
TWEETER AND MID -RANGE
Figure 4-Physical speaker layout of "3 -dimensional" stereo console.
sions of the console. The result is agreater area of sound source, whichpermits greater separation of the twoextension speakers without loss ofthe true stereo effect. The phasingof the two channels becomes lessimportant, since the "woofers" fillany "holes" which might appear inthe center of the "curtain" due to
use full -range speakers. The poten-tiometer is appropriately called a"focus" or "stereo centering" con-trol, because it appears to move thecenter of the orchestra.
STATUS OF PRESENT DAY STEREO
These latest improvements in thequality of stereophonic reproduction
STEREOSOURCE
FOCUS CONTROL
2-CHAN
PRE -AMP
PWR AMPS
RIGHT CHAN
FULLRANGESPEAKER
MIDDLE CHAN
LEFT CHANNEL
Figure 5-A method of obtaining a third or "Phantom" channel from two -channel stereo
phase differences. This amplifier alsouses two identical channels of ampli-fication.
The previously mentioned principleof the loss of directional effects atlow frequencies has led to the de-velopment of the Dual Voice CoilWoofer, specially for stereo use. Thisspeaker actually has two separatevoice coils on the same cone, one forthe low frequency notes from eachchannel. It thus combines these"lows" to provide the center channel.
Another method of providing thethird or "phantom" channel is shownin Figure 5. A tapped potentiometerbetween the two channels is used toprovide a signal to a third poweramplifier which feeds a full -rangespeaker. Both outside channels also
Sylvania News
have placed it in the status of high -
quality home entertainment. Present-day stereo has a depth of realism thathas to be heard to be believed.
SERVICE HINTSTIGHT GOVERNOR ASSEMBLY
The governor assembly of a signalseeker auto radio is no doubt tootight if the tuner does not respond tothe touch bar. To alleviate, simplypry up on the cross -bar bearing untilthe governor runs free when thetouch bar is depressed. Do not oil, asthis assembly must operate smoothly
September 1959
over a wide temperature range(winter to summer driving).
Harry MiklaszChicago, Illinois
SOLDERING IRON ALWAYS TINNEDTo keep the tip of your soldering ironbright and fully tinned, heat the tiparea to be tinned with an alcoholtorch and apply Silver Solder andpowdered borax flux. Since the tipwill never reach the temperature atwhich Silver Solder melts, the ironwill always stay clean and readyto use.
Floyd A. RobertsKearney, Nebraska
BALLPOINT PROBEDon't discard those empty 8 inchlong ballpoint pens. They makedandy insulated test probes for thoseout -of -reach test points on radiocircuits. Since the insulated hullsare not tapered, they can also beused for insulated sections behindalligator clips, etc.
Roy InlowSan Francisco, California
INTERMITTENTMOTOR DETECTOR
The relays on the motor control ofthe "600" series Zenith Space Com-mand T.V. Unit are very small. Thismakes it difficult to see if the contactsare closed. A simple check to seethat the contacts are closing can bemade by connecting a test light(preferably a 25 -watt bulb) to themotor control socket. Intermittentmotor operation will cause the bulbto light -up, making it very easy tospot while doing other bench work.
Lee LeBoeufOpelousas, Louisiana
VARIABLE LINE VOLTAGE SOURCE
In order to check a 3 -way portablereceiver's ability to operate at re-duced line voltage, a variable linevoltage source was needed. Nothaving a Variac, I installed a 110 voltoutlet on the panel of my tube testerand connected it to the filamentselector switch. By means of theswitch and line adjustment pot, theline voltage to the portable receivercan be varied to a point where the
7
SERVICE HINTSportable cuts -out. (Make certainthat the set does not exceed thefilament transformer rating of yourtester.) I have found that if theportable can operate with a linevoltage of 95V, it is unlikely to cut-out in the customer's home.
John E. HopkinsWillimantic, Connecticut
ANTENNA SPLICEWhen it is necessary to splice antennalead-in, the `overlap' method shown
will result in a much stronger spliceas compared to the common "butt"method. After the splice is made,the overlap is secured with tape.
R. BestosoMiddletown, R. I.
HEMOSTATS
Hemostats, such as are used bysurgeons for clamping blood vessels,effectively hold leads in place whilesoldering since they lock when closed.Due to the fact that they have fine,matching teeth, they will hold theleads of condensers, resistors, tran-sistors, etc. without slipping. Theyare also very thin, and fit nicely innarrow places.
Hemostats can be obtained in
various sizes from surgical supplyhouses; your local surgeon may haveused ones.
E. M. PrentkeShaker Heights 20, Ohio
SPEAKER CONE ALIGNMENTOff -center speaker cones can be easilyrepaired by removing the felt dustprotector so that the magnet can beseen from the face side. With ascrew -driver, pry gently on the sidethat is rubbing against the coil form.For more delicate speakers, wesuggest bending the frame slightly.After centering, reconnect the dustcollector with a good dope cement.
Roy NakanoSouth Bend, Indiana
TUBE INSERTER
The gadget shown below can bequite a time saver when insertingminiature tubes in hard -to -get -atsockets. Materials needed includea 7 and/or 9 pin tube shield; a 6"length of broomstick and an 8" pieceof 1/4" dowel.
To construct: Drill a 1/4" holelengthwise in the broomstick; cut orgrind off the closed end of the tubeshield; drive broomstick into end ofshield and shove the 1/" dowel intothe hole drilled in the broomstick.Depending on the type of shield used,the broomstick may need to betapered slightly.
To use, place tube into shield endof inserter, press tube in socket andrelease it from inserter by pressingend of dowel with thumb. To pre-vent breaking the tube tips, avoidplacing excessive pressure on thedowel.
W. L. SchloederLos Angeles 29, California
TUBE
TUBESHIELD
RUBBER
CUSHION
á
BROOMSTICK 1/4 DOWEL
WOOD COLLAR
RECESSED TOACCOMMODATE TIP
1/4 HOLE DRILLEDIN BROOMSTICK
8 September 1959
DEMAGNETIZE TAPERECORDER HEADS
A solder gun is an excellent de-magnetizer for tape recorder heads,watches, tools, etc. Just pass theobject to be demagnetized betweenor near the two poles of the soldergun with the switch "on".
Roy NakanoSouth Bend, Indiana
VIBRATORSUpon inserting a new vibrator in anauto receiver, it may fail to operateespecially if it has been laying aroundfor quite sometime. This is due totungsten oxide coating forming onthe contacts.
The contacts may be restored(cleaned) by applying 110 volts a. c.to the vibrating reed through a 40watt lamp for at least half a minute.Actually, six or seven minutes willdo no harm.
E. L. DeschambaultSt. Romuald, Quebec, Canada
SIMPLE FUSE CHECKWHILE ON SERVICE CALLS
To check any small T.V. or radiofuse in the field, simply remove theback cover of your two -cell flash-light; turn the switch to the "on"position; and hold the fuse, as shownbelow, so that one end rests on theend of the battery and the other endon the rim of the flashlight. (Ratingof fuse must be greater than currentdrawn by bulb.) If the fuse is good,the flashlight bulb will light. Thebrilliance will be in proportion tothe size of the fuse.
Harry HaskinsGreen Bay, Wisconsin
FLASHLIGHT
FUSE
Sylvania News
SYLVANIA NEWS
9
DELUXE
CITIZEN'S
BAND
(MOBILE OR
FIXED)
CONVERTERby
W. K. Boots, Field EngineerReceiving Tube Operations
The concept of using a converterahead of a standard broadcast re-ceiver for short-wave reception isnot new; nor are the advantages tobe gained, such as adaptation ofexisting equipment with little or nomodification. With the opening ofthe "11 -meter band" for CitizensRadio Communication, an 11 -meterconverter for automobile broadcastreceivers would seem to be a most
Sylvania News
TESECTION
OCTOBER 1959
VOL. 26, NO. 9
R. A. HUMPHREYS, TECHNICAL EDITOR This information in Sylvania News is furnished without assuming any obligations.
desirable and inexpensive approachto obtaining a mobile citizen's bandreceiver.
The converter described below wasoriginally designed for mobile use on10 -meters, where it proved to beexceptionally stable and sensitive.Its modification for 11 -meter. serviceis a natural adaptation of the circuit.The only changes required are inser-tion of a different crystal and retuning
October 1959'
the coils. There is no significantchange in performance in makingthese slight modifications on theoriginal model.
In operation, the converter circuitdoes not require adjustment andstation selection is accomplished bytuning the broadcast receiver dial,thus permitting push-button channelselection with receivers so equipped.A 6500 Kc crystal, provides direct
5
75f7167*OR
6AK5
TO CITIZENSBAND ANT.
.005
7059 *OR6UB
SIB TO# -4 HEATER
SUPPLY18
6.5 Mc 0.5
-.005 IOOKTO * TO
HEATERS.005 XTAL
1,0 m h,
50
* FOR 6 VOLT OPERATIONUSE 6AK5 AND 6U8'FOR 12 VOLT OPERATIONUSE 7176 AND 7059
100Alllf
L5
BCINPUT
lár ==1SiA -- RCVR
ANT.
INPUT2.5 mh.RFC
26 Mc
L4'on b`
B+150 TO250 V
1.005
BYPASS CAPACITORSARE DISC CERAMICS
(SIA,SIB GANGED)
RESISTANCE IN OHMS
CAPACITANCE IN ufds
Figure 1-Circuit diagram of Citizen's Band (Eleven Meter) Crystal Controlled Converter.
logging on the broadcast band, i.e.,26.965 Mc tunes at 965 on the dial,etc. While this method differs slightlyfrom conventional superheterodynesystems inasmuch as the intermediatefrequency (broadcast band) is vari-able; it retains the image rejectionfeatures of double conversion.
CIRCUITRY
The circuit shown in Figure 1 isconventional in that it uses a 6AK5for the broad -band RF amplifier, anda 6U8 for the oscillator -mixer. Theoscillator employs a quartz crystalwhich is operated on the fundamentalfrequency to provide good frequencystability. The fourth harmonic ofthe crystal frequency is resonated inthe 6U8 triode section plate circuit.Oscillator signal injection to the
6
mixer grid is automatically providedby the built-in tube -lead and socketcapacitances between the triode sec-tion plate and the adjacent 6U8pentode section control grid. A satis-factory 6500 Kc crystal, mounted inan FT -243 or smaller holder, may beobtained from the various crystalsuppliers or the surplus market.
If so desired, the Types 7167 and7059, which have 12 volt heaters andare designed for dependable heateroperation in mobile communicationequipment, can be used in place ofthe 6AK5 and 6U8. Also, the plateand screen voltages may be obtainedfrom the receiver power supply, pro-viding it will accommodate the addi-tional load, or an auxiliary packcapable of delivering 125 volts at 15to 20 milliamperes.
October 1959
The strong -signal handling capa-bilities of such a converter could beimproved by adding AVC bias to theRF stage. Since this necessitatesdigging into the receiver wiring, thisfeature is generally not included fora "connect -on" converter. However,a manual "local -distance" switch, S2is incorporated in the converter.
CONSTRUCTIONConstruction of the converter is notcritical in that considerable leewayis permissible in the parts layout, aswell as, in the choice of components.The unit is housed in a Bud Minibox,measuring 2 x 3 x 5 inches, which wasmodified to include a shelf. The com-ponent placement shown in Figures 2and 3, proved to be desirable espe-cially from the standpoint of wiringease.
Sylvania News
LI,L2
6AK5or
7167
L5
e. .L3
/1.?,
L6
6.5 Mc XTAL
6U8or
7059BC ANTENNAINPUT JACK
Figure 2-Citizen's Band Converter with cover removed. Note placement of componentparts. Entire unit measures only 2 x 3 x 5 inches.
OCS. CATHODECOIL
z
LOCAL- DIST.SWITCH
S2
L6
LI,L2
Figure 3-Under chassis view of Citizen's
The RF, mixer and oscillator coilforms, L2, L3 and L5, complete withshield cans were salvaged from anold 40 Mc television IF strip andeasily modified for 27 Mc operationper the coil data presented in Table I.
Sy!vania News
Band Converter. Note simplicity of wiring.
TABLE ICoil Data
L1, L2, L3, L5-%" diam. slug -tunedshielded forms
L1-3 turns #20 e close -spaced, woundover grounded end of L2
October 1959
L2, L3, L5-20 turns #30 e close -spaced
L4-20 turns #28 e close -spaced on1/4" diam.
L6-10 turns #20 e close -spaced on1/4" diam.
The builder can minimize unde-sirable stray coupling and therebyinsure foolproof operation by adher-ing to standard (good practice) wiringmethods; i.e., use short leads andcommon grounds for each stage.
ALIGNMENTAlignment of the converter isstraight -forward. The oscillator platecircuit, L5, is tuned for maximumsignal injection (4th harmonic of thecrystal) to the mixer grid. A VTVMis helpful for this adjustment; a read-ing of approximately two volts dcdeveloped at the mixer grid is ade-quate for good performance. Othermethods will also serve, such asadjusting the triode plate inductance,L5, for maximum indication on theS -meter of a communications re-ceiver, or absorption -type wavemetertuned to the fourth harmonic of thecrystal.
With the converter output coupledto the antenna input of a broadcastreceiver, optimum tuning for themixer grid circuit can most readily beaccomplished with the aid of a signalgenerator. Simply connect the signalgenerator output to the converterantenna input and set the dial toabout 27 megacycles. Keep in mindthat the broadcast receiver must betuned to about 1000 kilocycles inorder to receive the 27 Mc signal witha 6500 Kc crystal in the converter.Adjust the mixer grid inductance, L3,for maximum output from the broad-cast receiver, using as weak a signalfrom the signal generator as practi-cable. This is necessary for properalignment of the mixer free from"flattening" effects caused by AVCaction in the receiver. The RF stagetuning is not critical since it is pur-posely broad -banded.
It is recommended that the antennainput transformer, L2, be adjustedfor maximum performance with theconverter connected to the antennasystem with which it will be used."On -the -air" signals serve well forthis adjustment; although, tuning formaximum noise can provide satis-factory performance.
7
CONCLUSION tube. Be sure to cover the hole withWhile the converter described is in-tended primarily for use with auto-motive broadcast receivers, it willperform equally as well in fixedinstallations with "any" broadcastreceiver. It should be noted, how-ever, that full use of its preselectioncapabilities cannot be achieved unlessadequate receiver input shielding isemployed. While an auto radio meetsthis requirement, home radios maynot. If the home radio with whichthe converter is to be used employsa loop antenna, a switch must beprovided to disconnect the loop whenthe converter is in use. Otherwise,standard broadcast signals will con-tinue to be received, thus interferingwith the desired Citizen's Bandsignals. Additional shielding of theinput circuit may be required, evenin receivers that do not employ loopantennas. This will be determinedby the amount of broadcast feed -
through with the converter operating.A refinement to enhance mobile
performance would be the inclusionof a noise limiter in the auto receiver.The incorporation of the "TNS NoiseSquelcher," as described in the May1953 issue of C.Q., is a most worth-while project. This addition alsopermits receiver silencing duringstand-by.
SERVICE HINTSPROTECTIVE SOLDERING
When using a soldering gun it is notuncommon to accidently burn otherleads which may be rather close -by.This can be prevented by wrapping apiece of asbestos around the hot leadsleading to the tip. Stapling theasbestos will keep it in place.
M. W. ThompsonToronto, S. D.
EASY ACCESS TO TUNER TUBEIn order to replace a tuner tube insome of the older model TV sets, theserviceman has to remove the chassisfrom the cabinet. This task can besimplified (provided you have the setowner's permission) by cutting a 4 by4 inch hole. in the bottom of thecabinet directly beneath the tuner
8
a screen for safety.
Hubert J. DixonChurseburco, Indiana
PICTURE KEYSTONEDHORIZONTALLY
Although the effect seen in Figure 1is known to most servicemen as"Keystoning," the cause was slightlydifferent. Most sets exhibiting thisdefect are found to have defectivehorizontal deflection yokes; but thisparticular model had an open wind-ing in the plate circuit of the hori-zontal output transformer.
Robert E. ReddUnion Furnace, Ohio
ADDITIONAL EYEWhen inserting a Stylus or Crystal ina Phono arm, most of us have troublelosing screws and seeing what we aredoing. A compact mirror, placed inthe bottom of a small can, will notonly give you a view of the under sideof the Phono arm but will catchscrews if they should drop.
F. L. BrentonMason City, Iowa
ELIMINATE SPEAKER RATTLEYou may be able to eliminate speakerrattle and/or cone distortion bysimply inserting some ordinary ab-sorbent cotton between the back ofthe speaker cone and its chassis. Thisis an emergency remedy which canbe used on car radio speakers; thesmall cotton pads take up rattlesnicely.
J. PerkinsonMiami, Florida
YOUR
SERVICE HINTS C.
WANTED
Attention-Service Dealer readers ofSYLVANIA NEWS! What has hap-pened to the Service Hints columnover the past year? This column,which is supported by YOU, shouldinclude all technical hints believeduseful to your fellow Service Dealer.
For each hint accepted, you willreceive a certificate worth $10.00that can be applied against any ofthe many items listed in Sylvania'sAdvertising -Merchandising AidsBooklet. These items include: tools,tube caddies, technical manuals, dis-play signs and etc. If you are notfamiliar with this booklet, pick up acopy at your Sylvania Distributor orwrite to our Central AdvertisingDistribution Department, 1100 MainStreet, Buffalo 9, New York.
Perhaps you are not quite sure justwhat comprises a Service Hint. Itshould be nothing more than a simplemethod or device used to solve irri-tating or time-consuming serviceproblems. It could be that you havedevised a simple but unique methodfor servicing a remote section of achassis without removing it from thecabinet; maybe you've solved anelectrical problem peculiar to aparticular chassis-such as a remotecomponent being responsible for thedifficulty encountered in the sectionbeing serviced.
Any service hint which you feelmight be of value to you and yourfellow service dealer should be mailedto Sylvania Electric Products Inc.,Receiving Tube Operations, in careof the Technical Publications Sectionlocated in Emporium, Pennsylvania.
Sylvania is not obligated to returnany material submitted for publica-tion, whether or not published.
October 1959 Sylvania News
SYLVANIA NEWS
lit
iii
SECTION
NOVEMBERDECEMBER 1959
VOL. 26, NO. 10
R. A. HUMPHREYS, TECHNICAL EDITOR This information in Sylvania News is furnished without assuming any obligations.
WHAT THE SERVICEMEN TOLD TASOBy E. H. BODEN Advanced Application Engineer Receiving Tube Operations
Late in 1957, the Television Alloca-tions Study Organization (TASO)sent approximately 9,000 question-naires to television servicementhroughout the United States toprobe the problems involved ininstalling and maintaining antennas,transmission lines, the receiver itselfand allied accessories on both VHFand UHF. TASO sought to tap thevast knowledge and experience ofthe servicemen on all phases oftelevision reception.
ESTABLISHMENT OF TASOTASO was established by request ofthe Federal Communications Com-mission for collecting and examiningthose factors which should be appliedto the allocations of televisionchannels. Two hundred seventy oneengineers from 139 companies (9from Sylvania) worked for two yearsin the preparation of the report whichhas now been transmitted to theHonorable John C. Doerfer, Chair-man of the Federal CommunicationsCommission, Washington D. C.
The Engineering part of TASOworked under the direction of Execu-tive Director Dr. George R. Town.There were six panels, each with aspecific area of study.
PANEL 1-Transmitting equip-ment
PANEL 2-Receiving equipmentPANEL 3-Field testsPANEL 4-Propagation dataPANEL 5-Analysis and theoryPANEL 6-Levels of picture
qualityEach panel was made up of men
who were leaders in the field withwhich the panel was concerned. Thepanels were, in turn, made up of com-mittees, sub -committees and taskforces. Here again the most qualifiedmen of industry served to collect themassive amount of data which wasassembled.
PREPARATION OFQUESTIONNAIRES
Panel 3, with Knox Mcllwain of theBurroughs Corporation as Chairman,created committee 3.2 to prepare a
questionnaire which would providethe required VHF -UHF televisionreceiver installation, service and re-pair information. By late 1957, thequestionnaire was completed andapproximately 9,000 copies were sentout to the servicemen through ServiceAssociations and Manufacturers' Ser-vice Organizations.
Space does not permit the printingof all the questions asked, however,for those who did not receive one ofthe questionnaires, a brief descriptionwill now be given.
The questions were in six sections:A. General Information-Name and
address of the organization mak-ing the report, the area served,number of service calls, numberof antennas installed and a list ofthe stations received.
B. Receiving Antennas - Kinds ofVHF and UHF, height and lead-in information.
C. Receivers-Service problems withvarious types of receivers on VHFand UHF.
TABLE I
Channel Group Excellent Good Fair PoorAvg. Transmitting
E. Interference-Kinds of and com-parison of VHF with UHF.
F. Color Reception-Kinds of andcomparison of VHF with UHF.
DATA HANDLING
In March of 1958, TASO Committee3.4 was formed with Holmes W.Taylor as its Chairman. The respon-sibility of this committee was toreduce the data of the servicemen'squestionnaires to a form suitable for
much information was of interest andimportance to others ; in particularthose who had a part in its assembly.This was true for all of the panel andcommittee reports.
In the committee 3.4 report a mostinteresting and equally importanttable was computed. This table isincluded here as Table I.
For this table the distance to allstations reported as excellent wereaveraged for each of the channelgroups shown. Likewise for good,fair and poor.
able for reception in weak and strongVHF and UHF signal areas?
The computed percentages aretabulated in Table II.
From Table II we learn that 60per cent of the servicemen selectedyagis in a weak VHF area while35 per cent used corner reflectors ina weak UHF area.
It was also learned that for trans-mission line 82-94 per cent of theservicemen installed flat twin lead forVHF reception while 83-87 per centused tubular twin lead for UHF.
The committee received 730 copiesof the completed questionnaires from46 of the then 48 states (Delaware andVermont not reporting). Of the 541individually operating stations in thecountry, the survey covered 427which represented 79 per cent of thestations.
Each questionnaire received wasgiven a serial number by which it wasidentified from that time on. Theinformation was coded and trans-ferred to punch cards. A minimumof five cards were required for eachquestionnaire (those reporting onmore than four television stationsrequired an additional card.) Eachcard contained the serial number ofthe questionnaire from which thedata was taken.
Electronic computers and sorterswere then employed to make thedesired summations and tabulations.
THE RESULTS
When finally assembled, the datavaried in usefulness and importance.Some of the data was obviously ofimmediate importance, while otherdata will find use later.
Although the data collected wasintended for the Commission's use,
Table I then is a tabulation of theaverage distance of an excellent,good, fair and poor picture for eachchannel group.
On examination of the table, acurious oddity is evident in thechannel group 14-40. The good andfair figures appear interchanged.However, because of the low numberof UHF reports, the reversal is oneof those statistical events which statis-ticians can show to be a chance eventand has no significance. In short, afew more returns would possibly havealtered the data somewhat.
The serviceman can get a roughidea from Table I of how well a newstation coming on the air in aneighboring town will be received.The answer is found by knowing thechannel number and the distance tothe station and thus using Table I inreverse. For example, a station onchannel 10 and a distance of 40 miles.Consulting the Table, one may safelyconclude the signals will be fromgood to fair. It goes without sayingthat mountain ranges may causeweaker reception than that indicatedby Table I because of shading effects.
Another bit of very informativeinformation came in answer to thequestion-what type of outdoorantenna have you found most accept -
6 November - December 1959
Sixty per cent of those in combinedVHF and UHF areas installed sepa-rate lead-ins for reception of VHFand UHF while 40 per cent used thesame lead-in for both. When in-stalling VHF antennas, 53 per centof the servicemen explored for maxi-mum signal while 81 per cent ex-plored for maximum signal wheninstalling UHF antennas.
On the subject of ghosts, it wasreported that 12 per cent of the VHFsets suffered from ghosts, while 19per cent of the UHF sets had thistrouble. Asked on which sets ghostswere more objectionable, 321 re-porters said VHF by 69 per cent,UHF by 18 per cent and both VHFand UHF by 13 per cent.
GENERAL INFORMATION
A tabulation of the reported inter-ference sources at VHF and UHF isfound in Table III. Here one learnsfrom the reported data the kinds ofinterference most troublesome andthe relative effects on VHF, UHF orboth. Since the ratio of VHF andUHF data was consistently 2:1, thelast three columns should becorrected slightly for accuracy. How-ever, such is not necessary in view ofthe large ratios found under the
Sylvania News
per cent of interference between VHFand UHF.
Under general information it waslearned that servicemen made anaverage of 6,450 calls per year: 71.5%on VHF sets, 9.6% on sets with UHFconverters and 18.9% on sets withcombined VHF -UHF tuners. Thesefigures again point out that the ratioof VHF to UHF data was consis-tently 2:1.
HOW GOOD WAS THE DATA
Data can only receive its proper markof importance if it is accurate. Inthis connection the committee in-cluded the following statement in itsfinal report.
"A close study of the servicemen'squestionnaire indicated that thosemen who took the time to answer the
questionnaire were quite thorough.We received very few questionnairesincompletely filled out. There were,of course, a number of unansweredquestions for those areas that hadneither UHF, nor color service, andthis is the reason for the reducedresponse in those areas. In cross-checking the total results of varioussections of the questionnaire, thosewhich dealt basically with the sameproblem areas showed a very closecorrelation. Therefore, we believethis indicates that the serviceman didnot just make haphazard guesses, butwas particularly reliable in the way hewent about answering the questions."
Although the sample size (the 730returns) was a small percentage ofthe total number of servicemen in theUnited States and only those sets
requiring servicing were reported on,the committee felt because the datawas consistent, that the other service-men and receivers were statisticallyrepresented.
REMARKS
In view of the comments made by thecommittee, the servicemen may bejustly proud of their contributions toTASO and its great efforts. To whatdegree this or any other data will beused only time will ,tell. Committee3.4 drew no conclusions as was trueof the other committees and panels.All that can be said in conclusion isthat facts have been found and havebeen reported.
To the Federal CommunicationsCommission goes the task of drawingthe conclusions and using them.
YOUR SERVICE HINTS WANTEDAttention-Service Dealer readers ofSYLVANIA NEWS! What has hap-pened to the Service Hints columnover the past year? This column,which is supported by YOU, shouldinclude all technical hints believeduseful to your fellow Service Dealer.
For each hint accepted, you willreceive a certificate worth $10.00that can be applied against any ofthe many items listed in Sylvania'sAdvertising -Merchandising AidsBooklet. These items include: tools,tube caddies, technical manuals, dis-play signs and etc. If you are not
Sylvania News
familiar with this booklet, pick up acopy at your Sylvania Distributor orwrite to our Central AdvertisingDistribution Department, 1100 MainStreet, Buffalo 9, New York.
Perhaps you are not quite sure justwhat comprises a Service Hint. Itshould be nothing more than a simplemethod or device used to solveirritating or time-consuming serviceproblems. It could be that you havedevised a simple but unique methodfor servicing a remote section of achassis without removing it from thecabinet; maybe you've solved an
November - December '1959
electrical problem peculiar to aparticular chassis-such as a remotecomponent being responsible for thedifficulty encountered in the sectionbeing serviced.
Any service hint which you feelmight be of value to you and yourfellow service dealer should be mailedto Sylvania Electric Products Inc.,Receiving Tube Operations, in careof the Technical Publications Sectionlocated in Emporium, Pennsylvania.
Sylvania is not obligated to returnany material submitted for publica-tion, whether or not published.
7
Technical Section IndexAugust 1958, Vol. 25, No. 7, through December 1959, Vol. 26, No. 10
GENERALVOL. NO.
A Third Channel for Stereo 26 8Autodyne Converters 26 2Deluxe Citizen's Band (Mobile or Fixed) Converter 26 9Low Voltage AC Standard 26 5Simple Nomograph Eliminates Mathematical Manipulations 26 7Stereo in the Home (Part I) 25 7Stereo in the Home (Part II, Conclusion) 25 8Television Tuner Applications of Low Impedance Crystal Diodes 26 6What the Servicemen Told TASO 26 10
TELEVISIONLife Testing of Tubes in Television Receivers (Part I) 25 9Life Testing of Tubes in Television Receivers (Part II, Conclusion).. 26 1"Picture on the Wall" Television (Part I) 26 3"Picture on the Wall" Television (Part II, Conclusion) 26 4Screen Dissipation-Important Factor in Horizontal Deflection Tube Life. 26 7Your Television Screen 26 5
MISCELLANEOUS
Additional Information on Filament Voltage Test Unit ForHigh Voltage Rectifiers 26 6Sources For Thermocouples 25 7
Testing the Hybrid Auto Tube Types on the Models 137, 138,139 and 140 Tube Testers 25 8
It does not appear that the methodof displaying television just describedis likely to meet the criterion of cost,at least for home entertainment. Itwould appear, offhand, that 490conductors leading to the verticalcommutator and perhaps 550 to thehorizontal would be quite expensive.Other approaches have been pro-posed. For example, the use of aloaded transmission line or a lumped -constant line for horizontal scanningwith a lumped -constant line for
vertical scanning has been reported.
CONCLUSIONS
Many of the ideas that have been dis-cussed here have been demonstrated,but there remains a great deal to bedone in extending these and otherschemes to meet the requirements ofcommercial television. All in all, itappears that the advent of muraltelevision on a commercial basis isnot imminent. Before that dayarrives, however, there will be ample
use for the technique of the Sylvatronand similar devices for other formsof data display such as battlefieldsurveillance, missile tracking, stock-market listings and many otherswhere high speed and low cost re-quirements of television will not bartheir application.
This concludes the series of twoarticles entitled "Picture on TheWall" Television, the first part ofwhich appeared in the March 1959issue of SYLVANIA NEWS.
SERVICE HINTTOOL HOLDER
For those who do not mind mag-netized tools, the Ring Magnetillustrated below makes a dandy toolholder. In this case, the ring magnetused was removed from a discardedPicture Tube P -M E -M Focalizer.If more strength for heavy tools isdesired, two or more magnets canbe stacked.
Austin N. HubnerCincinnati, Ohio
ANTENNA INSTALLATIONFor those cases where a customer
doesn't mind an antenna mountedthrough his roof the followingmethod of installation will eliminateany possibility of the roof leaking.As illustrated in Figure 1, the greaterthe distance between the stud and theroof, the stronger the antenna. Thisinside distance also determines the
Sylvania News
length of the mast outside. The roofflange, which is designed to slip underthe shingle above it, should beapproximately six inches high andhave an inside diameter of 13/s inchesfor the mast to slip through. Thetight fitting funnel -shaped piece istaped to the mast to prevent waterfrom leaking through the roof flange.
It is then an easy matter to fastenthe 300 ohm lead-in to the antennabefore dropping it down the mast andout through the V2 inch hole in the2 x 4. A cork placed in the top ofthe mast then serves to keep most ofthe wiring out of the weather. Ifdesired, a rotor can be mounted atthe bottom of the mast.
R. BestosoMiddletown, Rhode Island
FUNNEL SHAPED P ECE
-.-1; HOLE FORMAST
tir
`-$HOLE FOR 300A LEAD2X2X4 CUT TO FITON CEILING JOICE
300 OHM LEAD TO TV
-Ilh- I;
ROOFFLANGE
FAULTY TAPE RECORDER?When servicing tape recorders the
first step is to determine whether therecording -playback head or amplifieris at fault. The two "Junk -box"items shown in Figure 1, whenproperly connected, can save plentyof valuable servicing time in theabove analysis.
The first is a solenoid which wasremoved from a relay. It should bebetween 200 and 400 Ohms D.C. or
April 1959
approximately 1,500 to 2,000 Ohmsimpedance. This solenoid is madeready for use by merely soldering toit a pair of wires approximately 12inches long.
The second item is a coil removedfrom a discarded TV picture tubefocal unit. With the cylinder or ringmagnet removed, two short pieces ofNo. 16 wire can be imbedded in theplastic coil form to serve as thecoil leads.
When servicing, disconnect therecorder head and substitute the relaycoil in its place. This relay coil isthen inserted in the focus coil. Withearphones connected across the focuscoil, you can hear whether or not theamplifier is operating, and/or whetherthe trouble is actually in the record-ing -playback head by simply talkinginto the earphones.
Austin N. HubnerCincinnati, Ohio
7
SUPPLEMENTARY TUBE TESTER SETTINGSListed below are important additions to the roll charts for Sylvania tube tester models 219, 220 and 620.Make sure your charts are completely accurate and up-to-date by adding these important facts now.
SECTIONR. A. HUMPHREYS, TECHNICAL EDITOR This information in Sylvania News is furnished without assuming any obligations.
YOURTELEVISION SCREEN
by J. B. Shinal, Picture Tube Operations
Service technicians are often ques-tioned by owners of television setsabout the appearance of undesirableimages and/or blemishes on thescreens of picture tubes whichdevelop throughout life. Severaltypes of blemishes, primarily due toimproper operation, can appear onthe screen as the tube ages. Beforereviewing these undesirable imagesand/or blemishes, let's examine a fewof the manufacturing steps designedto insure that the new screens ofSylvania Picture Tubes are of uni-form, superior quality.
One important reason why Syl-vania insists on new screens on everySylvania picture tube is that anyblemish caused by improper opera-tion would still be present on screenswhich are re -used.
MANUFACTURING TECHNIQUES
One of the first steps involves thecleanliness of the bulb. Even thoughthe bulb might appear clean, it is putthrough a series of mechanical andchemical washings in fluoride andcaustic solutions followed by anumber of rinses in extremely pureor demineralized water. This processactually removes a microscopic layerof glass exposing a very clean surface.
When the bulb leaves the washingoperation, it is next placed on a long,slow moving "settling" conveyor.The screening solution and the phos-phor particles in suspension areintroduced at this point. Prede-
Sylvania News
termined volumes of a weak acid ormineral salt and a silicate combine toform a gel -like solution, throughwhich the phosphor particles settleonto the face of the bulb. This gelledsolution creates a bond which holdsthe phosphor to the glass.
As the bulb reaches the end of thesettling conveyor, it is slowly tilted,as shown in Figure 1, to allow thesolution to pour off. An even layer
of the settled phosphor is left behindcovering the face of the bulb to formthe screen. If the tube is to bealuminized, screened bulbs are placedon a lacquering conveyor. A cushionof demineralized water is dispensedinto the bulb and a film of lacquerfloated on top of the water. After thelacquer forms an elastic film, thewater cushion ís decanted out from
(Continued on page 6)
Figure 1-As the bulbs reach the end of the settling conveyor, they are slowly tilted toallow the bonding solution to pour off. The bulb face is thus covered with an even layerof phosphor which settled through the bonding solution.
May 19595
Figure 2-The lacquer -covered screen is carefully inspected before the tube is approvedfor the next step in aluminizing.
Figure 3-As the bulbs are evacuated, the aluminum vapor condenses on the insidewalls of the tube, becoming the conductive and mirror-like aluminized screen backing.
under the film, leaving the lacquerdeposited smoothly on the screen.The bulbs are then dried with warmair as they pass underneath the con-veyor belt.
After inspection, see Figure 2, thebulb is placed over a tungsten coil
6
which contains an aluminum pellet.The bulb is then evacuated as shownin Figure 3. The tungsten coil iselectrically heated causing the alumi-num to vaporize; thereby coveringthe back of the screen and inside ofthe bulb with a microscopically thin
layer of aluminum. A test to de-termine the uniformity of the alumi-num coating is then made.
For both aluminized and non-
aluminized tubes, further processingof the screen includes baking forseveral hours at very high tempera-tures to remove any water vapor andother gases within the bulb. Bakingalso creates a stronger bond betweenthe phosphor and glass faceplate.Inspections before and particularlyafter baking insure further processingof only the highest quality screens.
Color of the finished excited tubeis a result of the initial blending andprocessing of the phosphors. Properblending results in a satisfactoryimage on the tube screen. (The whitescan range from bluish to yellowish,and the blacks from dark -bluish tobrownish in color). Controls exer-cised during the phosphor manu-facturing assure crystals of the propersize, color, brilliance or excitationand extreme purity.
B LEM ISHES
The most common blemish of non -aluminized tubes is the rough brownion spot appearing in the center ofthe tube face. This is usually due toan improperly adjusted ion trapwhich fails to remove the negativeions, (most of which originate at thecathode) from the electron beam.Improper adjustment may also de-posit metal on the screen. Properadjustment of the ion trap, (arelatively simple matter) will preventthis type of damage.
Another blemish, also common tonon -aluminized tubes, but due to asomewhat different cause, is some-times observed. Positive ions formedin the bulb space, or at areas subjectto electron bombardment, may resultin what is termed a "butterfly" or Xburn on the screen.
Excessively high electron beamcurrents can carry sufficient energy todestroy the efficiency of the phosphoritself. Sometimes when a set is turnedoff the beam is present momentarilywhile the deflection is off. A brightspot near the center of the tube canbe seen diminishing in intensity. Innon -aluminized tubes, and if notcontrolled for in aluminized tubes,excessively high electron beam
(Continued on page 8)
May 1959 Sylvania News
LOW VOLTAGE AC STANDARDD. J. Kelley, Technical Publications Section
While the electronic measuring equip-ment that is used in servicing isgenerally considered to be accurate;upon occasion, the user will havereason to doubt the validity of par-ticular readings. This is particularlytrue with equipment that is infre-quently used or is subject to rigorousfield usage. While it may ultimatelyturn out that the meter or scope, asthe case may be, is perfectly okay, itwould be handy to be able to elimi-nate or confirm one's suspicionsquickly and simply. To do this, asecond instrument must be soughtthat can be used to check out the first.For many of us this does not, how-ever, solve the problem, since thesecond instrument is usually one thathas been shelved because it is not ingood working order. What is reallyneeded is a regulated supply that willserve as a reference voltage. A dcsupply of this type is not difficult tocome by. Such is not the case whenac is involved; especially if thestandard must be capable of supply-ing a limited amount of power andhave an output wave -shape thatapproximates a sine wave. We mightthink, and rightly so, that the latterpresents a difficult design problemand could become expensive to con-struct. The circuit shown in Figure 2,while not the ultimate, will do thejob that needs to be done about theservice shop or home workbench andcan be constructed from parts thatare readily available.
This low voltage AC standard, thecircuit diagram of which was broughtto our attention by Mr. W. P. Muellerof our Advanced Application Lab,RTO, consists of three resistors, apotentiometer and a low voltagefilament transformer. The deviceuses two standard panel - lamps asregulators in a bridge circuit. Thesepanel lamps do not use sockets in thisapplication, but are soldered in placeto insure solid contact. Care shouldalso be taken to make sure the wiperarm on the potentiometer makessolid contact.
The solid curves in Figure 1 indi-cate the stability of the device at
2.0
1.9
L8
L7
1.6
15
14
1.3
1.2
1.0
0.990 95 100 105 110 115 120
LINE VOLTAGE IN VOLTS
125 130
Figure 1-The solid curves indicate the stability of the device at predetermined levelsof output voltage. In comparison, the dotted curves show the change in output voltage
for wide fluctuations in line voltage under conditions of 1000 ohms load.
various predetermined levels ofoutput voltage. Under no-load con-ditions, only a slight change in outputvoltage occurs for wide fluctuationsin line voltage. The reader will notethe existence of an optimum value ofoutput voltage at approximately 1.5volts rms.
As shown in Figure 3, this opti-mum value of 1.5 volts rms was thenused as the basis for determining thechange in output voltage for a changein load resistance. This curve wasobtained under average line con-ditions of 117 volts. Although theapplication may be somewhat
Sylvania News May 1959
limited, this curve indicates that thedevice is capable of supplying suf-ficient power to check meters havingan input impedance as low as 1000ohms per volt.
As indicated in Figure 3, the sta-bility of the device started to dropoff slightly at 1000 ohms and below.For comparison purposes, data wasthen taken to determine what changethere would be in output voltage forwide fluctuations in line voltageunder conditions of 1000 ohms load.The dotted curves in Figure 1 illus-
(Continued on page 8)
7
Figure 2-Circuit diagram of the Low Voltage AC Standard.
I.8
.s
1.5
1.4
1.3
12
100
117 VOLT LINE CONDITION
2 3 4 6 6 7 8 9 10 2 3 4 5 6 7 6 910
500 ;OOO 5P00 10,000
LOAD RESISTANCE IN OHMS
2 3 4 6 6 7 8 910
50,000 100000
Figure 3-This curve, which was obtained under average line conditions, illustrates theminute change in output voltage over a wide range of load resistance.
trate this comparison. Again, notethe degree of stability at the optimumvalue of 1.5 volts rms output.
This device, which can beassembled by the average home -builder in a matter of minutes, maybe used not only to check the accu-racy of low voltage ac meter rangesbut that of external scope standardsas well. Since it is remarkably stable
8
for wide fluctuations in line voltage,the user can be sure of 1.5 volts rmsoutput. The flexibility of the deviceis practically unlimited in that, theexperimenter may, for a particularapplication, change the output bysubstituting different components.The use of a bridge circuit also offersthe possibility of regulating in eitherdirection.
YOURTELEVISION
SCREEN(Continued from page 6)
currents can lead to destruction of thephosphor, causing a small brownisharea on the unexcited screen. Furthertreatise on the subject is covered inthe article "The Case of the Con-tinuing Spot" which appears in theOctober 1957 issue of SYLVANIANEWS Technical Section.
In aluminized tubes, screenblemishes due to ion activity withinthe tube are non-existent; the alumi-num film protects the screen from ioncharges. However, rough handlingduring shipment may cause looseparticles of material inside the tube,resulting in a small hole or scratchon the screen.
Perhaps the most common blemishis due to the fact that a charged tubeis an excellent dust collector. Com-plaints of decreased brightness canoften be traced to a very dirty tubeface and adjacent mask.
IMAGES
The raster outline can be seen on theunexcited screen of tubes which mayhave been improperly operated, orwhere the raster has been reduced insize and so operated for a long periodof time.
Afterglow on the entire rasterwhich is noticeable after the set isturned off in a darkened room usuallyindicates a phosphor of high per-sistence. That is, the phosphor stillemits light after the exciting electronstream has been removed. Sometimesthe image of the last scene presenton the receiver can be seen for sometime.
The total result of the entire tele-vision system, from studio camera,through transmitter and receiver cir-cuits and finally the picture tube, ispresented to the viewer on the allimportant picture tube screen. Thisis why Sylvania concentrates majorengineering effort on perfect screens,and provides a new screen made bythe very latest techniques in each andevery non -aluminized and SilverScreen 85® aluminized picture tube.
May 1959 Sylvania News
In the Interest of the "Independent." .. .
NEW SYLVANIA ADVERTISING FEATURES ;
"Tubes Tested Free"-three wordsthat can help lose ór win, plenty ofsales dollars for you! Make sureyou're on the winning side. Takeadvantage of Sylvania's newest ad-vertising and promotion program tohelp you build your business in thehighly competitive radio -televisionconsumer market.
Sylvania's new advertising pro-gram has been especially developedto help you, the independent service -dealer, effectively combat increasingcompetition from other sources ofretail supply - consumer buyingsources that have been attempting toincrease business through the offerof "free tube testing."
The "do-it-yourself" trend reachedover into electronics recently whenspecial tube -testing machines wereplaced in stores selling directly toconsumers. Many of these storesremain open on Sunday and attemptto attract TV parts consumers bytelling them that the machines areavailable for their use at no charge.
Against competition from suchoutlets as drug stores, chain stores,general variety and hardware stores,the independent service -dealer mustwage a positive and continuous salespromotion campaign to get a fairshare of the expanding "do-it-your-self" tube replacing market. That'swhy Sylvania has designed thisspecial advertising program aroundthe "free tube testing" theme.Many service -dealers throughout thecountry are now facing damagingcompetition from other retail outletswhich feature tube -testing to attractconsumer traffic.
SURVEY SHOWS SALES THREAT
The service -dealer is currently thenumber one source of consumer tubesupply. However, when Sylvania'smarket research department went outto get the facts about "do-it-yourself"tube replacing, it found certain
principal cities where independentservice -dealers were not gaining inreplacement sales. For example, inthe city of Indianapolis, approxi-mately 14 per cent of consumer tubesales were not made by independentservice -dealers. Here's a breakdownof the per cent of receiving tubespurchased by type of store accordingto the Indianapolis survey:
Independent service -dealers, likeyourself, must remain by far the
number one source of consumer tubesupply if your business is to expand.The best way for you to fight the "do-it-yourself" threat in your area is withSylvania's advertising program.
THREE POINT DEALER PROGRAM
Sylvania's special, local consumeradvertising program, built around the"tubes tested free" theme featuresthree important sales promotionitems that can help you combat the"do-it-yourself" trend and increaseyour sales volume. The companyhas invested thousands of dollarsin preparing a colorful windowstreamer, a counter card and specialnewspaper ad mats. They are allavailable to you through your localSylvania distributor.
NATIONAL ADVERTISING PROGRAM
Continues in "Best Read" TV GuideSylvania's big, new national adver-
tising campaign keeps the spotlighton the company's TV smog consumertheme and the "independent service -dealer" in the pages of TV Guide.
Featured as "America's best readmagazine" TV Guide will spotlighttwenty-six full page ads during 1957,giving millions of TV set owners theconvincing sales message of "TVSmog."
The latest TV Guide ad, illustratedhere, urges consumers to "make surethe next picture tube is a `SilverScreen 85'."
The more than 5,000,000 readersof TV Guide find out, through everySylvania ad, that they can get a TVsmog rating from the man who dis-plays the new independent Service -Dealer Emblem.
TV parts consumers, who con-stantly refer to the pages of TV Guidefor program listings and featurearticles are urged to treat themselvesto brighter, clearer, "smog free"
71-TV SMOG may be o
sign your picture tube is overage
.511..y,Screone.mo:.
...td.,wv
nroke sure your next picture tube is u
"SILVER SCREEN 85"(}@r
((\1 ¡\ (r
-X A7JAtl1\lA
pictures by replacing the old wornout picture tube with a "Silver Screen85" picture tube.
The powerful full page ads appearin everyone of the forty-four localeditions of the popular TV partsconsumer magazine.
2March 1957 Sylvania News
"TUBES TESTED FREE" CONSUMER THEME
WINDOW STREAMERAND COUNTER CARD
Sylvania's colorful new glascenewindow streamer will bring "do -ityourself" customers into your shop.Urging customers to "replace withdependable Sylvania tubes" the eye-catching streamer features the big,bold letters "tubes tested free." Thecounter card, which resembles anofficial certificate, will remind con-sumers who visit your shop that theyneed not go elsewhere to have theirreceiving tubes tested without charge.Both the window streamer andcounter card are available free fromyour Sylvania distributor.
LOCAL NEWSPAPERADVERTISEMENTS
Sylvania has prepared special ads foruse in your local newspapers featur-ing the "tubes tested free" theme andspotlighting the independent service -dealer emblem, tying you in with thecompany's powerful national con-sumer advertising campaign on "TheBuccaneers" and in TV GUIDE.
There's a special place on eachad where the name and telephonenumber of your shop can appear inbold letters. These ads are available,in mat form, free from your Sylvaniadistributor.
This eye-catching, colorful window streamer will help increase your tube sales.
HELP YOURSELF TO MORE SALES
You'll be helping yourself attractmore "do-it-yourself" fans and win-ning more radio -TV parts consumersas regular customers by taking ad-vantage of Sylvania's new "tubestested free" advertising campaign.
The colorful window streamer, theattractive newspaper ads are designedto attract more consumers to yourshop. Once inside, even the mostavid "do-it-yourself" consumer canprobably be influenced to let you
"Do -It -Yourself" fans will stop at your shop when they see these special ads inyour local newspaper.
service his television set. As an ex-perienced radio -television technician,you can show him that replacingparts in electronic equipment can notonly be dangerous but costly. Takeadvantage of this chance to not onlyincrease your tube sales, but buildyour service business, too. See yourSylvania distributor now for com-plete details on how you can receivethe three special sales promotion itemsin Sylvania's big, new "Tubes TestedFree" independent service -dealer ad-vertising campaign.
Sylvania's attractive counter card servesas a reminder to have YOU test their tube.
Sylvania News March 19573
Help Yourself To More Sales .. .
PUT YOURSELF IN THE CUSTOMER'S PLACEBy JAMES W. RITTER, Sales Training Manager, Electronic Products Sales
Many millions of dollars are spenteach year by manufacturing organi-zations such as Sylvania, yourindependent distributor and your-self to build a solid reputation forindependent service -dealers as "head-quarters for complete radio andtelevision servicing."
When a TV parts consumer entersyour shop, or when you enter acustomer's home, it's your oppor-tunity to win a steady customer bygiving prompt, courteous service.Only by maintaining a large activelist of "satisfied customers" will yourbusiness succeed!
How do you go about winningfriends and influencing customers?There are hundreds of importantpoints that should be consideredwhen the subject of customer rela-tions is approached. But, there isone simple formula that usually willhelp create a positive impression inanyone's mind. Merely do more ofwhat they like and less of what theydislike.
Is your attitude toward everycustomer who enters your shop oneof helpfulness? Do you try your bestto make him feel at ease and as ifyou are really interested in givinghim good service? Greeting yourcustomer with a friendly smile andthe pleasant words "may I help you,please" doesn't cost you a cent. Itmay help you increase your sales
volume.
Good or bad, it's a well-knownprinciple that people form opinionsquickly. The old adage "a first im-pression is a lasting one" seems to beespecially true when it comes to the"customer." This principle appliesnot only when you're behind theservice counter in your shop but whenyou're visiting the home of a TV partsconsumer, too.
When three or four customers de-scend upon your shop at once, do youpolitely acknowledge the presence_ ofeach and quickly service each in histurn? Is your merchandise attrac-tively displayed for the customer'sbenefit so that he may take advantageof this waiting time to "browse a bit."
Many items which you carry inyour shop can turn out to be plussales for you if you put them withinreach of the consumer.
One of the most important pointsto remember in applying some of thetried and true techniques of "sales-manship" is to avoid blunt, positivestatements that do not allow for "giveand take." If a customer indicates apreference for a specific productwhich you do not have in stock, yourchances of losing the sale altogetherare better if you imply by expressionand tone of voice that it is an inferiorproduct, anyway. Rather, if youcourteously explain that you aretemporarily out of stock on this itemor that you don't carry it because,while it's a quality product, you feelthe same product made by the XYZpeople is better, you may still makethe sale.
Never put yourself in the positionwith a customer where you may geta negative reaction from him. It'susually more advisable to recognizethe reasons behind the customer'schoice-then persuade him to buythe "better" product which youstock. In a positive manner, alwayssell up the products you stock-neversell down competition. It's not goodsalesmanship and isn't it the goodsalesman who makes money?
To many radio and TV parts con-sumers who haven't the slightest ideawhat a 2N229 transistor is and neverheard of a 6BQ6GTA, electronics isthat mysterious "something."
Certainly you should never talkdown to your customers, but don'tmake the mistake of trying to impressthem by using technical languagewhich makes no sense to them.
And, if you take the time to explainyour job to the customer, it oftenmakes the bill for your services moreacceptable.
Don't forget that you're just asmuch of a salesman when you're in acustomer's home. Always look likewhat you are-a professional radio -television technician. Little thingslike leaving bits of wire and tubecartons in a living room can teardown a customer's opinion of you.Be sure you place your tools so thatthey will not scratch the TV set orother furniture.
Make your first rule on homeservice calls, "courtesy and neat-ness." You'll be helping yourself tomore sales.
Everything you do in handlingcustomers should build confidencein their minds. People are facedeveryday with the problem of whereto buy. They like to feel that theirchoice is the best. You can con-tribute to this feeling of confidenceby being honest and sincere in yourdealings with customers. An ex-cellent way is to follow up on yourservice jobs. In most cases, a tele-phone call or one of those eye-catch-ing Sylvania consumer postcards willfill the bill.
Customer good -will is often neg-lected in day-to-day activities and weshould constantly be on the alert todo things that the customers like.A good yardstick to apply is to putyourself in the customer's place-ifyou like it, he probably will, too.And remember, customers are theonly indispensable factor in ourbusiness.
