SYLVAN ITechnical EditorNEwsIt. A. Humphreys

TECHNICALSECTIO\

July 1968 VOL. 35 - ISSUE 3

CHROMA AMPLIFIERS

Most service technicianshave a good understanding ofmonochrome television and can,without reference to a schematic,state what the waveforms gen-erally should be throughout thecircuit. In a color receiver, thesignals from the antenna to thevideo output, including syncand AGC, are identical to a mon-ochrome receiver. The infor-mation which must be processedto provide color is contained inthe composite video signal.

Therefore, processing of thecolor information contained in thedetected video signal is the essen-tial difference between mono-chrome and color TV receivers.The color signal contained in thecomposite video is located in anarrow bandwidth of 1.0 Mhzwhich is centered on a suppressedsubcarrier of 3.58 Mhz. This colorinformation or chroma signal isremoved from the video by a take-off circuit tuned to 3.58 Mhz.Amplification, demodulation andmatrixing are the three processingstages required to provide colorsignals at the grids of the threeguns in a color picture tube. Ourconcern here will be with the am-plification of the chroma signaland the effects of control voltagessupplied to the chroma stages.

Chroma amplifiers, or bandpassamplifiers, as used in present daytelevision receivers can be classi-fied into two general types. Let'scall them simply the "One -Stage"and "Two -Stage" amplifier sys-tems. Block diagrams are shownin Figure 1 with the chroma por-tions enclosed in dotted lines forcomparison.

byR. F. Bergdahl

FROMVIDEO-IF

L

COLORDEMODULATOR

Figure 1 A. "One Stage" Color System.

Figure 1B. "Two Stage" Color System.

One -Stage System

A typical "One -Stage" amplifiercircuit with corresponding oscil-loscope waveforms is shown inFigure 2. In this arrangement,the 1st video amplifier stage alsoserves as a chroma amplifier byproviding an amplified chromasignal output. The chroma signalis removed from the video by a3.58 Mhz series tuned circuit atthe plate. This chroma signal isthen used to drive both the burstamplifier grid and the chroma

amplifier grid. Notice that thechroma control grid circuit is re-turned to the killer bias source.This permits the chroma amplifiertube to be cut off with a negativekiller voltage when a burst signalis not present or to operate nor-mally when the killer voltage isremoved with the presence of aburst signal. Cut-off of the chromaamplifier prevents the display ofcolored snow when no color signalis received.

The output of the chroma ampli-fier stage generally ranges fromten to thirty volts peak -to -peak

FROMVIDE , IFDETECTOR

COMPOSITEVIDEO

VIDEOOUTPUT

1st VIDEO AMPLIFIERmaim

HORIZONT.:.L1TE -/`^.^ -

PUT

*MONOCHROME AND COLOR INFORMATION;AND SYNC PULSES

CHROMASIGNALWITHBURST

gingLURST AMPLIFIER

CHROMA SIGNALWITH BURST REMOVED

CHROMAOUTPUT TO

DEMODULATOR

BLANKING PULSES

BURSTOUTPUT

Figure 2. Chroma "Bootstrap" Amplifier Circuit.

FROMVIDEO IF --IDETECTOR

I

COMPOSITEVIDEO SIGNAL

CHROMASIGNALWITHBURST

Ist CHROMA AMPLIFIER

ACCBIAS

B+O

HORIZONTAL

*MONOCHROME AND COINFORMATION; AND SYNC PULSES

CHROMASIGNALWITHBURST

.dr 1#1

2nd CHROMA AMPLIFIER

KILLERBIAS

GATEINPUT

LOR

BURST AMPLIFIER

CHROMA SIGNALWITH BURST REMOVED

fCH ROMAOUTPUT TO

DEMODULATOR

BLANKING PULSES

BURSTOUTPUT

NamFigure 3. Two Stage Chroma Amplifier Circuit.

depending on the demodulatordrive requirements, but in allcases, is from a low impedanceoutput circuit of approximately500 ohms. The low output imped-ance is necessary to prevent inter-action between the chroma signalapplied to the demodulator tubeand the carrier signal from the3.58 Mhz oscillator also suppliedto the demodulator tube. The out-put signal from the chroma ampli-fier stage would normally containthe burst pulse that is part of thechroma signal. Since the burstsignal is of sufficient amplitude,and occurs during horizontal re-trace time, a brightening of theretrace lines on the CRT screenresults. To prevent this, a positiveblanking pulse is applied to thegrid of the chroma amplifier tube,thereby removing the burst fromthe chroma signal driving thedemodulator control grid.

chroma amplifier ges Thecontrol grid of the 2nú r,.romaamplifier tube is returned to akiller bias source which providesa high negative voltage to the grid,cutting the tube off when a signalwith no color burst is received.The presence of a color burst sig-nal removes the bias from the 2ndchroma amplifier grid permittingnormal amplification of the chromasignal. The output of this tuberanges from 10 to 30 volts and is alow impedance suitable for drivingthe demodulator tubes.

The color gain control for eitherthe "One -Stage" or "Two -Stage"circuit can be a variable resistancein the cathode of the chroma out-put tube, a potentiometer in thegrid circuit of the chroma outputtube or a potentiometer across thesecondary winding of the chromaoutput transformer, the latter beingthe most commonly used method.

Figure 4. Oscilloscope Demodulator Probe.

Two -Stage SystemA typical "Two -Stage" ampli-

fier circuit with associated oscil-loscope waveforms is shown inFigure 3. In this circuit, thechroma input signal has beentrapped from the detected videosignal and applied to the grid ofthe first chroma amplifier. Sincethis tube is used exclusively forchroma signals, an automatic colorcontrol bias (ACC) can also beapplied to the grid to stabilize theburst and chroma output level.This ACC voltage regulates thechroma signal level in the sameway that the AGC regulates theaudio signal level in a radio.

The output of the 1st chromaamplifier then drives both theburst amplifier and the 2nd

Trouble -ShootingWhen trouble -shooting chroma

circuits, there are several checksthat can help in your analyses andperhaps pin -point the troublefaster. First, be sure the problemis actually in the chroma circuits.Proper setting of the channel finetuning is necessary to receive thecolor signal. Correct tuning canbe achieved by adjusting the finetuning control towards the soundbars, then backing off slightly toobtain a sharp color picture.

The color killer circuit can bemisadjusted so as to cause inter-mittent color or a complete loss ofcolor. The color killer control isusually adjusted with the receivertuned to a snowy signal or a blankchannel. The control is set tocause confetti or colored snow,then backed off to eliminate theconfetti.

Ghosts which would not benoticed on black and white cancause severe shifts in colors.Antennas and lead-in's should bechecked for broken lines or cor-roded connections. Impropermatching of lines feeding two ormore TV receivers can cause inter-ference and reflections which mayprevent color reception on somechannels.

Locating a problem within thereceiver with an oscilloscope cansave time if certain precautions aretaken. Tuned circuits at the in-put to the first chroma amplifierand burst amplifier are generallycritically tuned and scope probecapacitances can cause severedetuning or loading. Do notexpect the same receiver perform-ance with probes attached; they

Figure 5. Overall Chroma Response Curve.

will, however, ndicate the pres-ence of the chroma or burst sig-nals. The additional capacity ofa probe may cause reduced colorgain or . hifts in color hue. Mea-surements of DC voltages on thegrids of the chroma amplifier tubesisolate chroma amplifier problemsfrom bu st and color killer prob-lems. With a color signal beingreceived, the chroma amplifiergrids should be near zero voltageor slightly negative. Negativevoltages in excess of 3 to 4 voltsusually indicates malfunction ofthe color killer.

The alignment of chroma am-plifiers is straightforward. Thesame sv'eep and marker equip-ment us ;d for video IF alignmentwill usi ally handle the chromafrequency of 3.58 Mhz. The onlypossible additional item neededwould be a demodulator scopeprobe if you do not already haveone. A demodulator probe circuitis shown in Figure 4. This par-ticular probe has a low inputcapacitance to minimize circuitloading.

The sweep and marker gen -

1erators- are generally tied in aheadof the chroma circuit just after thevideo IF detector. The demodu-lator probe is attached to the sec-ondary of the chroma outputtransformer.

Tjhe typical chroma responsee is shown in Figure 5. It has

bandwidth of 1.0 Mhz with ac.erf ter frequency of 3.58 Mhz.

moikerally,the chroma take -off

is adjusted to peak at 3.58 Mhz%hale the chroma plate transformeris tined to peak at 3.08 Mhz and4. 0 Mhz with the top and bottomcore adjustments. When align-meie is required, the receivermanufacturers' procedures shouldbe followed for best results.

To summarize the operation ofchroma amplifiers, regardless ofthe circuit used, they are narrowband rf amplifiers operating at3.58 Mhz. They operate with in-put signals as low as two volts toprovide 10 to 30 volts output acrossan impedance of approximately500 ohms. Voltages influencingthe operation of chroma amplifiersare: The input chroma level, theACC grid bias, the horizontal

blanking pulse, the color killerbias and the adjustment of thecolor level control. The outputsignals provided by the chromaamplifiers are: A chroma signalwith burst which is fed to the burstamplifier and a chroma signalwithout burst which feeds thecolor demodulator tubes. In somecircuit applications, the burst isremoved from the chroma signalwith a blanking pulse at the colordemodulator tubes. Other circuitsapply the blanking pulse to thechroma amplifier tubes to removethe burst. The presence of burstin the color signal applied to thepicture tube grid causes a bright-ening of the retrace lines duringburst time.

Take care to avoid the pitfallsof circuit loading with test probes;problems with associated circuitschanging the voltages to thechroma amplifiers; check for colorand burst signals at the controlgrid of the chroma amplifier; andfinally, follow the receiver manu-facturers' recommended proce-dures for the servicing and align-ment.

S LVAN IA T E C H N I CALSECTION

Terhnieal Editor April 1968 VOL. 35 - ISSUE 2R. A. Humphreys J

X -Radiation and the service technicianby H. C. Pleak, Manager Commercial Engineering

Department Electronic Tube Division

As much has been saidabout X-radiation during thepast year ... this article presentsa brief discussion of X-rays andwhat they may mean to the manthat services a color TV re-ceiver. Included also is whatSylvania has been and is doingabout X-radiation from tubes.

IntroductionA German physicist, working

with a Crook's gas discharge tube,discovered in 1895 that some typeof unknown rays, given off by theoperating tube were fogging uphis photographic plates. Sincethey were unknown rays, thephysicist used the algebraic X(for unknown) and called themX-rays. The world rememberedthe physicist by naming the unitof X-ray dosage after him theRoentgen (pronounced Rentgen).The X-ray dosage rates we shall bediscussing are in the range of oneor a few thousandths of Roentgens(milli Roentgens) per hour, abbre-viated to mR /hr.

Since Roentgen's discovery,almost three quarters of a centuryago, there has been an immenseamount of knowledge accumulatedupon the theory of generation,application, detection, and thedangers associated with X-rays.Let's talk a little about each oneof these items.

How X-rays aregenerated

Without going into a lot ofcomplexities ... When high speedelectrons are stopped suddenly

by hitting atoms or elements (suchas in a metallic surface), theenergy of the electrons is con-verted to electromagnetic radia-tion. A portion of this electro-magnetic radiation is known asgeneral X-radiation. Speaking ingeneralities, detectable X-rayscaused by abrupt deceleration orbreaking of the electron beamsare only generated by electronbeams which have been acceler-ated at voltages in excess of 15,000volts. Each species of chemicalelement also gives off X-rays char-

acterized by unique wave lengthswith the higher atomic weightmaterials giving off short wavelengths and the lighter materialslonger wave lengths. All X-raysare capable of passing throughsome material with a transmissionwhich is inversely proportional tothe density of the material beingpenetrated. This characteristicmakes X-rays most useful in thefield of diagnosis, particularly med-ical, but also in such diverse fieldsas pipe line weld quality andmechanical part fit.

Figure 1. Ionization Chamber --Basic Precision Instrument For Measuring X -Ray Radiation

This information is furnished for the professional RadioTV Service Dealer without assuming any obligation.

Figure 2. Dosimeter-Personnel TypeDosage Indicator Is Worn On Person.

X-rays are usually describedas being "hard" or "soft". Com-parative hardness is determined bythe speed (accelerating potential)of the electrons which caused theX-rays. The accelerating potentialin the case of dental X-rays may bein the 50 kilovolt to 75 kilovoltregion, while medical X-rays forX-ray plates or treatment may bein the 75 kilovolt to 150 kilovolt

region. Industrial X-ray equip-ment for analyzing welds andmachinery may use acceleratingpotentials exceeding a millionvolts. In terms of comparativehardness, the dental X-ray is theleast hard, or relatively soft of thewell known X-ray sources. Themaximum potential capable ofcausing generation of X-rays in aproperly operating TV receiver isapproximately 25 kilovolts. So incomparison with dental and medi-cal X-rays, this is, indeed, a verysoft X-ray source-with very lowpenetration capability.

As explained previously, inorder to generate X-rays, we musthave a stream of electrons acceler-ated at fairly high potentials andstop these electrons abruptly.There are three locations in a colorreceiver where these conditionsfor X-ray generation can be met;the high voltage rectifier, the highvoltage shunt regulator, and thepicture tube.

X-ray detectionIn order to determine the

presence of X-rays, we need ameans of detecting and measuringthem. X-rays ionize air in their

Figure 3. Survey Meter-Reads Dose Rate Per Hour of An X -Ray Field.

path causing electrical conduction,so one means of detecting X-raysis to use a form of condenser withair as a dielectric. In use, thecondenser is charged and placedin the path of the radiation wherethe ionized particles dischargethe condenser. The amount ofdischarge is proportional to theamount of X-ray radiation receivedfor a given length of time. The unitis called an ionization chamberand is considered to be the basicprecision measurement instrumentfor X-ray radiation, Figure 1. Incomparison, however, with otherX-ray radiation measuring devicesthey are somewhat bulky and re-quire skilled personnel to handle.

A second, personnel, type ofdosage indicator (called a dosi-meter) is a film badge. Exposureto X-radiation sensitizes the photo-graphic film. Upon developing,the degree of darkening of thefilm is a measure of the X-ray dosereceived. The film calibration anddevelopment is a skilled and highlyspecialized procedure.

Pocket dosimeters working onthe ionization chamber principleare also available for monitoringof personnel dosage in such places

SYLVAN IAEditor N Ews

D../ames McCue

PROvOTIO\SECTIO\

April 1968 VOL. 35 - ISSUE 2

Sylvania Sco, effgainBRIGHT ONFeaturing The SensationalSylvania Dealer Sweepstake!

Sylvania has done it againwith a big, brand new award pro-gram-the most exciting andimaginative in the industry!

Your Sylvania distributorwill award you one "On Target"check for every 50 Sylvaniareceiving tubes purchased-regardless of type. Thesechecks will be redeemable forfabulous gifts to suit your everymood and pleasure.

Here is the smart way toincrease your profits, capture agreater share of the market inyour area and, by selling qualitySylvania receiving tubes, in-crease your customer loyalty-all while piling up those valu-able "On Target" award checks!

Everyone a WinnerCheck your Sylvania dis-

tributor-you may have alreadywon! In addition to all the spec-tacular "On Target" prizesoffered, you have an opportunityto win one of the 1,017 majorsweepstake prizes-including a1968 Dodge service van, a 1968Dodge Coronet 440, a great vari-ety of color TV servicing equip-ment and much, much more!

Every listed Service Dealerwill receive a Sweepstake an-nouncement with a "DealerSweepstake Award Check" en-closed. Rush this check to yourSylvania distributor where youwill find a listing of all the win-ning numbers-check this list,if your number appears-you'rea winner-it's that simple!There is no purchase required-void where prohibited by law.

Even if you don't win one ofthe big prizes, you may stillredeem your sweepstake checkfor one of the thousands of glam-orous "Bright On Target" prizes,when combined with dealer "On

Target" award checks issued onyour Sylvania tube purchases.So you see, Sylvania has comeup with a program that makesevery participating dealer awinner!

Dealers not receiving a copyof the Sweepstake announce-ment may obtain entries by writ-ing to: Sylvania Dealer Sweep-stake Headquarters, P.O. Box7020, St. Louis, Mo. 63177.

N THIS SECTIOSylvania's Entertainment Program-Bright On Target!1968 TV Guide ListingsNew Magnetic Vinyl SignSylvania Has the Best IDEASYears Ago inSylvania News -1948

Sylvania Sponsors

the Most Exciting

Program in

TV Guide .. ."MAN IN MOTION"

STARRING YOU!

Yes, you can star in TV Guidethroughout the year billed as anexpert in color TV service andrepair!

You still can be featured inthree big issues; June 8, September21 and November 16 as the "ManIn Motion"-a dealer on the movewho uses Sylvania qualityproducts. Each ad will list your

name, city and phone number.Along with your TV Guide

listing, you will receive a com-plete, business building promo-tional package that includes athree dimensional clock sign andwindow display spotlighting youas the "Man In Motion'-the mankept busy doing expert TV repairsand servicing.

This total program was de-signed to bring you greater profitand recognition-what better waythan a listing under the Sylvaniatrademark in America's mostwidely read TV magazine?

Your Sylvania distributor cantell you how you can still becomea part of this program in time forthe next listing. So get in motion!

EasyOnlOff

MagneticVinylSign

You can now transform yourfamily car into an advertisingvehicle for use during your work-ing hours. Just use this new, brightyellow, red, black and white signto identify you and your servicesto potential customers in your area.

This 81/2" x 11" sign easilyadheres to any metal surface-files, counters, trucks and cars.When you're using your car forpleasure-just remove the sign-no trouble or fuss! This is anextremely inexpensive way to con-vert your business/family car intoa vehicle advertising your services.ET -1849-$3.50 each.

Sylvania Announces The BrightestColor Picture Tub er e!

Sylvania recently emphasizedits position as the industry leaderby introducing the brightest pic-ture tube in the history of colortelevision! This was achievedthrough a series of coordinateddevelopments involving majorcomponents to the tube. The newpicture tube is 23% brighter thanits nearest competitor and de-livers a more vivid, more realisticpicture than heretofore possible!

This new picture tube repre-sents the second major advance incolor TV brightness in less thanfour years. Sylvania also led theindustry in 1964 with the devel-opment of a europium "rare earth"red phosphor which enabled theconsumer to view the picture in a

normally lighted room.

40 Million Picture TubesSylvania entered into 1968

with the production of its 40millionth picture tube. Our SilverScreen 85 is a quality leader in theBlack and White television marketand we have continued those qualityobjectives with the manufactureof color picture tubes.

With the introduction of thisnew color bright 85® picture tube,Sylvania has once again dramatic-ally reaffirmed its leadership bydeveloping the most advancedcolor picture tubes available inthe industry today.

As always, Sylvania is "BrightOn Target!"

A Sylvania engineer is shown measuringthe new tube's brightness (lower set) with aphotoelectric cell. The brightness level isdisplayed on the monitor (upper set) viaclosed circuit TV.

IdentifyYourself AsAn Expert

In TVServicing

The colorful, new dealer de-cals highlight you as an expert incolor TV servicing and identifyyou as the person to contact fortop quality Sylvania color bright85® and Silver Screen 85® picturetubes.

It adheres firmly and easily toany smooth surface: windows,counters and trucks ... no water

required. When placed on yourwindow, the 71/2" x 10" doubleface sells your services insideand out.

Made of weather and faderesistant material, this decal willlast for years.

Order your supply today.ET -1921-25 cents each.

Light Up A Winner!

CJ

SYLVANIA

color brhfigpicture tubes

When you carry an outstand-ing picture tube you should let itbe known with an outstanding sign!The Sylvania color bright 85®clock sign was awarded a top prizeas a superior Point -of -Purchaseitem in a recent national competi-tion. Another professional recog-nition of Sylvania's winning formin consumer attracting signs anddisplays!

At $24.95, the color bright85® clock sign is also a winnerprice wise-Order one from yourSylvania distributor. ET -1915.

New TypesAddedBySylvania

I

Type Description

3CB6 Pentode for use as IF amplifier in TV receivers.3CF6 Replaces 3CB6 and 3CF6.

6LH6A Beam triode for use as a shunt regulator in the high volt-age power supply of color TV receivers. Used by GE.

6LJ6 Low current, high voltage beam triode for use as ashunt regulator in high voltage power supply of colorTV receivers. Used by GE.

Sylvania HasThe Best Ideas!Since its introduction slightly

over two years ago, the ElectronicComponents color motion pictureIDEAS has been viewed by anaudience in excess of 60,000people in almost 2,000 differentlocations. Recognition from thefilm industry reads like a Who'sWho of Awards in movie making:The Columbus Film Festival, theAmerican Film Festival in NewYork and the CINE '67 Awardamong others, have all accordedrecognition in the industrial filmcategory to IDEAS.

The interest that has beenexhibited in the IDEAS film andthe story of our contribution toelectronics has further helpedidentify Sylvania as an industryleader. The content and messageis as current today as it was on itsinitial showing.

If your group would like tohave the opportunity to view thisexcellent film, it is available bywriting to: Sterling Movies, 43 W.61 St., New York, N. Y. 10023or 309 W. Jackson Boulevard,Chicago, Illinois 60606.

Years Ago In Sylvania News: 1948

Quantity

VIZIXIMMIlf:40;,,,Zz:rf;c1 OMEight of Ten 1947 Passenger Cars Radio Equipped

Qcb)«Firm demand for new passenger automobiles now being produced at the 1941 rate,

GCand the increasing number of new car buyers taking a radio as original equipment

, will provide a good market for auto radios during 1948, according to the director ofsales research for Sylvania. 9,, Y

c, !

00/Vat. > v+ > . , . , . , . w- , . -v, . , (Yesterday, A Sylvania radio in every car -- tomorrow,a color bright 85® picture tube in every home!)

ORDER COUPONOrder any item from your Sylvania distributor or mail this order form to:

Sylvania Electric Products Inc., 1100 Main Street, Buffalo, New York 14209

Description

ET -1921 --Dealer Decal @ $

Price Total

.25 ea.

ET -1849 -Magnetic Vinyl Sign C $ 3.50 ea.

ET -1915 -color bright 85®Clock Sign C $24.95 ea.

Include Applicable Tax $

GRAND TOTAL $

NAME

STREET ADDRESS

CITY, STATE and ZIP(Please Print)

i

Figure 4. Steel of Proper Thickness is An Effective X -Ray Shield.HV Rectifier and Shunt Regulator in Well Designed Receiver Are Housed in Steel Enclosures.

as the vicinity of atomic reactors,Figure 2. They read a value ofreceived dose which may be amilli Roentgen in 1 hour (1mR perhour); or perhaps a Roentgen in20 days of continuous 10 hour perday use or 5mR per hour; or inother words, the total dose re-ceived in any measured lengthof time.

A different type of instrumentused to continuously indicate doserate is called a survey meter,Figure 3. It reads the dose rateper hour of an X-ray field. Some-times the survey meter is called acounting rate meter since it countsthe rate of discharges of a Geiger-

Mueller tube ... whose dischargesare proportional to the intensity ofthe X-ray radiation. A prospector'sGeiger counter falls in this cate-gory as do various other countingrate meters of superior precisionand stability for laboratory radia-tion survey work.

All of these devices indicatethe presence of X-ray radiation,but their use for absolute measure-ments is not for amateurs or theunskilled. For example, ionizationchambers can be affected by co-rona discharges. Some instru-ments are seriously affected, andindeed worthless, in a pulsed RFfield such as developed by a

horizontal flyback transformer.While the ionization chambers arenot completely directional, lowlevels of radiation will be detectedin a directional mode. Prospector'sGeiger counters are very sensitiveand can indicate presence ofX-radiation, but unfortunately, theindication is most probably in-correct by extremely large factors.This is due to the output variationof the Geiger -Muller tube at vari-ous X-ray energy levels, and ex-treme calibration inaccuracies inthe low energy (about 25 KV)region. Further, Geiger countersare extremely directional and aninordinate amount of experienceand knowledge is required toprobe an X-ray field and obtainmeaningful results. X-ray intensityfrom a point source drops off asthe square of the distance from thesource. But, since Geiger counterspick up those rays emanating froma surface, it is possible to obtainhigher measurements farther fromthe source. This is because thedetection probe sees a largersource of X-rays, all of which canbe most confusing and meaning-less to the uninitiated.

IntensityX-radiation increases with

voltage and current. A high volt-age increase accompanied byan electron current increasevastly increases the amount ofX-ray radiation. Shielding materialwhich was adequate at one voltageand current level may not neces-sarily be adequate for a higherlevel. This is similar to a flash-light behind an opaque glasspanel. You can't see the flash-light, but if a powerful arc light isused, the light shines right throughthe supposedly opaque panel.Generally as an X-ray beam getsharder and harder, the effectiveefficiency of the shielding materialis reduced.

ShieldingThe soft X-rays developed by

a color TV set can be partiallyattenuated by many materials,such as wood, pressed board, card-board, glass, etc. All reputableAmerican manufacturers use aglass containing a high percentageof the chemical element lead (highatomic weight and high density)for the envelope of high voltagerectifiers and dc shunt regulators.Lead, of course, is an effectiveshielding material.

Shielding of soft X-rays can be

accomplished by any of the heavymaterials (high atomic weight).For example, the high voltagerectifier and shunt regulator inwell designed receivers areshielded by steel enclosures ap-proximately .010 to .015" thick,Figure 4.

The real and implied dangersof X-radiation to the viewing publicand to the service technician havebeen bandied around, cussed, anddiscussed ad infinitum. Manu-facturers always will meet, orbetter, state or government re-quirement ... but legislation maybe no protection against problemswhich can develop at the servicebench.

Sylvania and X-raysSylvania has, of course, al-

ways been most conscious of theX-ray safety problems associatedwith high voltage devices. Withtelevision sets operating at }sighvoltages over 15 Kv and set manu-facturers desiring even highervoltages, it has long been a Syl-vania directive that "no tubesintended for use at or above 15 Kvshould be made with envelopesother than lead glass." Continuouslaboratory evaluation of the X-radiation from the Type 6BK4shunt regulator resulted in aproduct control specification to be-.mitten coincident with y plume:meproduction. The manufacturing

techniqueb processes, as wellas metall»=gical developments anddesigns which produced the highreliability Sylvania high voltagerectifiers for color TV were alsoinstrumental in maintaining thelow levels of X-radiation found inthese tubes. Engineering and pro-duction groups are, of course,continuously working to reduceX-radiation even lower.

PrecautionsThe TV technician can and

should take precautions when per-forming service work on colorreceivers. Even though well de-signed receivers have more thanadequate shielding around thosetubes capable of developing X-rays, the service technician mustoften "trouble shoot" with theshielding removed. A malfunction-ing tube can yield high volumesof soft X-rays for short intervals,and these are the types of troublethe service technician is hunting.The service technician shouldalways remember that his eyes areone of the most seriously affectedpart of the body where X-rays areconcerned. He must, for his ownsafety's sake, be alert to mal-functions (arcs, shorts, red anodes,and glowing particles) and kill theset power immediately. Of course,he mu__ ok :erve normal highvoltage safety precautions.

A few do's and dont'scan be helpful:

1. The receiver manufacturer hasfurnished straightforward set-upinstrumentions for his receiver.Follow these in detail.

2. After set-up, check out thereceiver's high voltage per-formance with an accurate highvoltage meter. Insure that thehigh voltage stays within therecommended range with vari-ous adjustments of the frontcontrols, and over expected linevoltage variations.

3. Do not routinely remove protec-tive shielding in preparationfor servicing.

4. Develop troubleshooting tech-niques that circumvent operat-ing the set with the high voltagecompartment open.

5. Don't get closer to high voltagesections than is dictated by safehigh voltage practice.

6. Do not attempt X-ray surveyswith Geiger counters-they arenot intended for this work!

7. Don't examine at close distancesmalfunctioning high voltagecomponents. Wear safetygoggles if you do not wear eyeglasses.

8. Tree t both high vi-'tae*e andX-íay sources with respect.