TM 11-273 RADIO SETS SCR-193-A,B,C,D,E APRIL 1941

8/10/2019 TM 11-273 RADIO SETS SCR-193-A,B,C,D,E APRIL 1941

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SCR-193-B

NDSCR-193-E

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RDEPARTMENT,

NGTON,April12,1941.

ft^l93-D,andSCR-193-E

raph

________________ 2

reception___ r____ 3

*-_________________ 4

__________________ 5

_________________ 6

_ 8

_ ---------9

_________________ 10

____ ______________ 11

1-AandBC-191-C,

tsTU-5-Aand

______________ 12

ndBC-312-C_ ----- 13

__________ -______ 14

________________ 15

andBD-77-B--- 16

53,andmast

_______________ 17

8,BX-19,and

78,BG-79,BG-84,

ndcabinet

______________ 19

__________________ 20

__________________ 21

__________________ 22

ortooperation___ 23

_________________ 24

_________________ 25

__ 26

__________________ 27

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parts.Paragraph

1-AandBC-191-C,

tsTU-5-Aand

andBD-77-B__ 30

dBC-312-C31

iotransmitters

e,andvoltageread-

ilure37

ddimensions40

reception3

1-AandBC-191-C,andtransmittertuningunits

ndBC-312-C13

15

andBD-77-B16

53,andmast baseMP-3717

-8,BX-19,andBX-2118

78,B.G-79,BG-84,androllsBG-56,BO-56-A,


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TC.

CE-193-A,SCR-193-B,SCR-193-C,

-Earedesignedforinstallationinvehicles

gintervehicularcommunicationwhether

ormoving.Modificationsmayappear

ttheseradiosetsto newtypesofvehicles,

gesin thismanualwillbeissued.

SCR-193-B,SCR-193-C,SCR-193-D,

edforusein lighttankM2A3,scoutcaf

car M3A1,andtruck,%-ton,4x4,

ively.Thesesetsmayalsobeinstalledin

batteryisavailableandifproper shielding

ovided.Theseradiosets havebeen

mbersbecauseofminordifferencesin

rytoeffectsuitableinstallationsinthe

ned.

ructionshereinapplyequallyto all

manualunlessaparticularoneis specifically

r.

primarysourceofpowerrequiredto

ndreceiversofthesesets isthe12-volt

notaradioset component).Fornormal

nsumptionofthereceiversandtransmitters

eration,seeparagraph36.

ershaveanominaloutputratingof75

ndreception.Theseradiosets

llowing:

graphsignals,abbreviatedas"c.w."

nuous-wavetelegraphsignals,abbre-

nuous-wavetelephonesignals,abbreviated

distancebetweenstationsoverwhich

tablishedwiththeseradiosetswill vary

donthe frequencyandthemodeofopera-

tmospheric,andelectricalconditions.

liablerangesofthesesetsin milesareas


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Thereceiversofthesesetshavea

o18,000kilocycles(kc.).

frequencyrangeof1,500to 4,500kc.

smittertuningunitTU-5-Aisemployed,

00to3,000 kc.Whentransmittertuning

quencyrangeis 3,000to4,500kc.

uencyseparationrequiredbetween

mevicinitydependsuponseveralvariable

smittingandreceivingstations.

verswithwhichthetransmitteris likely

ftransmission.

onequivalenttoapproximatelyonepercent

mployedispractical.Approximately75

arationareavailable,providingsetsadjacent

thana fewmiles.

93-A,SCR-193-B,SCR-193-C,SCR-

aybeusedintwo-waynetcommunication

rtypesoftransmittingradiosets listedin

ure1,providedall radiosetsusedarewithin

ngeoftheleastpowerfulset.Figure1

sofradiotransmitterswhicharea com-

setsandthebandsof theothertypesof

em.Authorizedfrequencieswhichlie

dsmaybeselectedforsuchcommunication.

hiclenamedinparagraph1isprepared

llthenecessarymountingholesandmany

radioinstallation.Theignitionsystemis

mpere-hourstoragebatteryisinstalled,anda

mployedinthevehicletomaintainthe charge

tionrelativetothe installationofthese

esignedforvehicularuse.Suitable

dedtopreventdamagefromexcessive

enotstockedascompleteunitsbutare

partswhicharerequisitioned,stored,and

heSignalCorpsGeneralCatalogis con-

componentparts,theyareindicatedinthis


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ETC.

UnitTU-6-A

0040004500

equencybandofradiotransmittersBC-191-AandBC-191-O.


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a.Theapproximateweightsand

dsetsareas follows:

sofcomponentsaregivenindetail in

a.RadiosetSCR-198-A.Thissetis

ighttank M2A3.Themajorcomponents

91-A.

sTU-5-AandTU-6-A.

.

MS-53,inclusive,andmastbase

BX-8,BX-19,andBX-21.

BG-78,BG-79,androllBG-56.

-A.

.Thissetisdesignedforinstallationin

thesamemajor componentsasdoesthe

ptthatitemployscontrolboxBC-309,

onboxTM-188andbox BX-21.Other

elengthof cordsnecessarytointerconnect

erly.

Thissetisdesignedforinstallationin

isesthesamemajorcomponentsas

exceptthatinadditionit employsa

orbulkhead,andspacersforthecontrolbox

Thissetisdesignedforinstallationin

rcomponentsofthissetare

91-C.

-C.


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ETC.11-12

TU-5-AandTU-6-A.

MS-53,inclusive,andmastbase

BG-78,BG-79,BG-84,androll

-21,andcaseCS-48.

carrytypenumbersdenotingachange

ofradiosetsSCR-193-A,SCR-193-B,and

ngesineachofthesemajor components

Thissetisdesignedforinstallationhi a

d(radio).Itcomprisesthesamemajor

diosetSCR193-D,exceptthatcovers

-84,andboxBX-21arenotfurnished,in

mponentsareinstalledin cabinetCH-60.

reinthelengthof cordsnecessarytoniter-

arts.t

-191-AandBC-191-C,andtrans-

andTU-6-A.Thetransmitter

arehousedi nametalcabinetcomposedof

op,sides,back,and bottomsupportedby

itterincludesacalibrationchart,pilott

ountingFT-151-B.Eithertransmitter

dinto acompartmentintheleftfrontpart

thetuningunitfrontpanel becomesapart

el.Extensionsatthe cornersofthe

ittercabinetareprovidedfor securingto

eleasingthesnapslidesofthismounting

ted fromthemounting.Releasingtwo

ontof thecabinetpermitsremovalofthe

andprovidesaccesstothetransmittertube

thetubecompartmentshieldandthe

ccesstothefilamentresistorconnection

kplatepermitsaccesstoothercircuit

er.Thecalibrationchartisheld inplacein

ertuningunit byaframeandfour thumb-

tralizingcapacitoradjustmentmechanism

vingthischart.Foursocketsare provided,

tsideand alongthebottomofthetrans-

etsofnecessarypowerandcontrolcords.

ersareprovidedtoprotectunusedsockets.


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ETC.

tterBC-191-A,withtubecompartmentshieldandtopcoveroff,tubes re-

ningunitTU-5-Ainplace.

minetheinstallationused.Ventilation

hesides,back,andtubecompartment

ntingFT-172isfastenedtothevehicle

rovideadditionalsupportforthe


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rds

tterBC-191-A,rearview,shieldsremoved.

2andBC-312-C(figs.5and6).The

ina metalcabinet.Thecircuitelements

nt panelandchassisassemblywhichis

hecabinet.Thisassemblyissecuredinthe

knobsonthe frontpanelandmaybe

nellockknobshi acounterclockwise

foursnap-slidecatchesatthebottom

ber shockelementsofmountingFT-162.

T-178isfastenedtothevehicleandto the

videadditionalsupportforthereceiver.

andmountingFT-162areincludedas

g.7).Thiscontrolboxconsistsofa

othe vehiclebymeansofametalbracket.

econtrolknobsandfourscrewson the

stotheinterior elementsofthebox.

309(fig.8).Thiscontrolbox

dly securedtothevehiclebymeansoffour


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TC.


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ate.Removalofthefour screwsinthe

aseprovidesaccesstotheinterior elements.

7-AandBD-77-B(fig.9).Eachof

ynamotoruponwhichismountedametal

theunitisprovidedwithfour snap-slide

nittothe mountingFT-107.Socketsand

holein theleft-sidepaneloftherelay fuse

tleads.Releasingthefour snapslide

elayfuseboxpermitsremovalofthe cover

elementswithinthebox (fig.10).The

untingFT-107areincludedas partsofthe


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ETC.

MS-53,andmast baseMP-37

ectionsaremadeofhigh tensile-strength

MS-49formsthetopof theantenna

C-321,frontandtopview.

and theothersfollowinsequenceoftheir

onMS-53screwsintomastbaseMP-37,

boxBC-309.

he vehicle.Alargehelicalspringinthe

onalflexibilitytotheantenna.Theupper

terminatesina bluntpoint.Thelower


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fittedwithaserratedshankandscrewfor

perendsofthe nextmastsections.Ends

blinghaveenamelmarksofthe samecolor.

tBD-77-A.

enameledblackandbears thetypenumber

alllength oftheassembledantennais

oxfordynamotorBD-77-A.

sBX8,BX-19,andBX-21.Case

nto whicheitheroneofthetransmitter


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ETC.

edand mountedorcarried.Thetuning

bythesamefour snap-slidecatchesthatare

hetransmitter.BoxesBX-8andBX-19

ansmitterand sparetubesforthereceiver,

arriesspareparts,andthemicrophone,

otinuse.These boxesmayberigidly

e.

dmastsections.

BG-78,BG-79,BG-84,androlls

netCH-60.a.Covers.CoverBG-67

ckandis placedoverthemastbaseMP-37

use.Itis securedtothemastbasebya

ebottomof thecover.CoversBG-75,

eofheavywaterproofedcanvasduckand

mitter,anddynamotorunit,respectively.

sof coversBG-75andBG-78maybe

tothefrontpanels ofthereceiverandtrans-

edbyopeningthe slidefastenersmaybe

rsonthe topsofthecovers.Openingson

ecoverspermittheentryof connectingcords

ThepreparationofscoutcarM3A1by the

rtheinstallationofradiosetSCR-193-D

acabinet42%incheslong, 25%incheshigh,

efrontof thiscabinetiscoveredbycover

nentlyfastenedtothetop ofthecabinet.

3-Disnot inservice,thecoverissecured

etbydotfasteners.Whentheradioset

ice,thefrontofcoverBG-84isrolled

cebythreewebbingelementswhichare

meansofsuitablypositionedsnap fasteners.


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dBG-56-Aaremadeofblackcanvas

etsof fivemastsectionseachinseparate

X


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TC.

binetCH-60is53%inches long,29%

sdeep andisdividedbyone verticalparti-


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ucted,onecoveringtheleftcompartmentand

rtments.Thedoorsarehingedabovetheir

pportionswingsoutwardanddownwardto

on.In thisposition,thedoorsareremova-

bya verticalmovementofthedoorassem-

ntdisengagesoffsetbrackets,weldedto

emblies,whichengagea portionofthe

nthedoorsarein place.

.a.Ajunctionbox(fig.12) isinstalled

mbatcarMlAlbytheOrdnanceDepart-

ofconnectionsfortheradioset SCR-193-A

ountedterminalblockTM-183,

djackJK-34-A.

12,13,14,and15) isinstalledduring

clenamedinparagraph1.Init aremounted


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TC.

ebatteryconnectionsandbracketsforthe

ckTM-183.Theterminalboxiscon-

(whereused)by conduit(fig.12).


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iortooperation23

etshavetheusuallimitationspossessed

mepower,mobility,andfrequencyrange.

4)andthe channels(par.6)mustbecon-

hichareaffectedbymanyfactors,the

econtrolledbytheuser oftheset.Some

ntrollablearelisted belowandrequirethe

setsareto operatemosteffectively.

otherthingsbeingequal,distance

tinperfectconditionthroughfrequent

ofalldefects.Forinspectionprocedure,

cetotone,andeitherc.w.or tonein

ransmitterandreceiver.

ns,eithernaturalorman-made,parti-

nces,suchastallmetalstructures,and

egraphlines.Thetypeandcontourofthe

ndchangeoflocationtoa morefavorable

longerantennathanthat normallyused

ennalongerthanthe standardmast

dbetweenthemastbaseandatree orother

thispurpose.

eonly veryshortdistancesaretobe

edecreasedandinterferencereducedbythe

t sections.

ngsbeingequal,thenumberofchannels

a(l)(a),(6), and(c)above,particularly

ciesasfarapartas possibletonetswhich

chotheron theground.


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ETC.23

Particularcaremustbeobserved

ngtheequipment,becausewhennotpro-

kmountingsitmaybe easilydamaged.

yfordamagewhenremovingitfromthe

,cleanwithbrushorblowerbefore

informationrelativetotheinstallationof

allationinstructionsfortheparticulartype

instructionsareissuedseparatelytousing

seoftheirvolumeandpossiblechanges,will

nual.Figures12,13,14,and15 showthe

gdiagramsoftheradio setswheninstalled.

norinstallationsaremadeasindicated

ntrols,knobs,switches,jacks,etc.,

hereafterbedesignatedbysuchmarkings.

witchonthefront panelofthetransmitter

VOICEabovethethreepossiblepositions

witchwill hereafterbedesignatedthe

AandBC-191-C.(a)Ifnecessary,

thesocketbehindtherubyreflector

entvoltmeterandthetotalplatecurrent

his isaccomplishedbyremovingthe

partmentshieldandinsertcorresponding

markedwiththerespectivevacuumtube

s.

edinthe relayfuseboxassociatedwith

-AandBD-77-B.Ifnecessary,replace

ndFU-18asthecasemaybe, andas

fusemounting.

TU-5-Aor TU-6-Aandinspectthe

inthelowerportionof thetransmitter

ovethetuningunitcompartment.See

ce(fig.4).

.G.insulatedwire,usingtheminimum

weenbindingpostsmarkedLOAD-Aand

nalpostsmarkedCSPEand GNDto

nner.Thesebindingposts arelocatedon

TRIP(fig.2).

BC-S12-C.(a)Inserttwopilotlamps

eaccessibleuponremovaloffourthumb-

ecuredthereby,fromthefrontpanel.The


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ringthemain tuningdialdirectlyabovethe

acethereflectorafterinsertionofthe

yfurnishedwith testedvacuumtubes

rinterchangethesetubesunless they

tive.Ifnecessary,disconnectthepower

ocketsmarkedwiththerespectivevacuuin

mbers.Thesesocketsareaccessibleupon

andchassis assemblyfromthecabinetwith

e CWOSCILLATORandRFOSCILLA-

CWOSCILLATORtubesocketisacces-

pfront screw,removingascrewinthe

seninga screwatthebottomrear,andthen

tcover.TheRFOSCILLATORtube

ooseningtwoscrewsatthetop rightside

rof thecompartment.

tspriorto operation.

equipmentinvolvestheuse ofhigh

roustolife.Operatingpersonnelwillobserve

es.Donot changefusesormakeadjust-

iththehigh-voltagesupplyon.

edinspectionoftheinstallationand

nparagraph336andcorrectwherenecessary.

eration.Aftermakingtheabovecheck,

esforthetransmitteras follows:

gs.12,13,14,and 15)fromtheradio

motor.Theseplugsandtheirintercon-

voltagesupplyfromthe dynamotortothe

rfromthetube compartment.

n therearofthe tubecompartment

e filament-resistorconnectionboard

tchin thetubecompartmentinthe

tpanel,set theTONECWVOICEon

L switchonCWFIL.

ehicleand accelerateuntilthevehicular

eandthe batteryvoltagerisestoasteady

FFONswitchinthe ONposition.

motorandapply filamentvoltagetothe


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ETC.

ubes. Usingascrewdriverora short

2B&S orlarger),andstartingat theex-

ILAMENTrow,successivelyconnect

WFILAMENTrowandastudin the14V

g. 16).Oneachconnection,thetube

filamentvoltmeterwillindicatetheapplied

onisfoundthatwillcausethe filament

s,placetheOFFONswitchin theOFF

betweenthetwostuds justselected.

Eswitchon VOICEandtheCW

DFIL.Repeattheoperationin (8)

ODFILAMENTrowofstudsandthe

storconnectionboard.

nderit forthestudsusedin operation(8)

tremerightendoftheMODFILAMENT

ILswitchonCWFILandthe

VOICE.PlacetheOFFONswitch

FILAMENTvoltagewillnowbeless

emannerasin(8) above,startingwiththe

connectionmadein(8) aboveandsucces-

connectpairsof studsontheCOMPand

ndwhichcausesthefilamentvoltmeterto

FFONswitchto theOFFposition.

estudsjust located.


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vehicleoffandplacethe12V 14.2V

CEswitchon CWandtheCWFIL

OFFONswitchinthe ONposition,

getofall toasteadyvalue.Thefilament

o belessthan10.5volts.With ascrew-

opperwire(No.12B&S orlarger),starting

oftheCWFILAMENTrow,successively

ntheCWFILAMENTrowthe12V row

onnectionisfoundthatcausesthefilament

s.PlacetheOFFONswitchin theOFF

onglinkprovidedbetweenthepair ofstuds

CEswitchon TONEandtheCW

DFIL.PlacetheOFFONswitch

endoftheMODFILAMENTrow,in

ve,successivelymovetotherightuntila

ILAMENTrowandt"he12Vroware

amentvoltmeterto read10.5volts.Place

FFposition.Connectthelong link

ofstudsjust located.

witchinthe 14.2Vposition.When

motorhasstopped,replacethetubecompart-

eplugsPL-59in thedynamotorand

lamentvoltagehasnowbeenadjusted

tingconditions,thevoltageatthe tube

be10voltsunderall conditionsofoperation.

Whennecessary,specialadjustmentsare

graph35.

a.Interference.(1)Interferenceis

onandbythe useofthecrystalfilter.

buteasourceof interference,particu-

ncies.Avoidoperationinthevicinityof

calledtrackstatic,maybegenerated

hisformofinterferencemustbecured at

ueto improperjoiningofmetalparts

entedbycare ingroundingtheradioequip-

gtogether(connecting)allmetalpartsof


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ETC.24

rationmaycausethethermostatsin

ducenoise,inwhichcasetheheaters should

rference,andotherswhichmaybe

ce,mayusuallybeidentifiedbytheir

perationisprescribed,eachsetin thenet

tothesamefrequency.Frequencyadjust-

dwiththeaidof afrequencymeter.Tune

etundersubstantiallythesameconditions.

of theantenna,thetemperature,andthe

mustbefairlyuniform.Avoidtuningin

uildingsandmetalstructures.Ifopera-

ted,tunesetswithenginesof thevehicles

ercontrolsafterthenettuning operation.

(1)Alwaysoperatethetransmitterwith

particularlyimportantin netoperation

orrectfrequency.Tonetransmission,being

et operation,butproducesmoreinterfer-

han doesc.w.transmission.Voicetrans-

erferencethandoestonetransmission.

eration,andtoinsure thatthereceiver

rntheHEATERSOFFONswitchofradio

positionfor15 to30minutesprior to

at positionduringoperation.

llnotbetooselectiveduringstand-by

LPHASINGcontrol,whichcontrolsthe

theOUTposition.

rols.-Observecareinhandlingallofthe

equippedwithstops tolimittheirmove-

yonditsnormalstopwill seriouslydamage

onappliesparticularlyinthereceiverto

,CRYSTALPHASING,andVOL.

erialnumbersoftransmittertuning

hthe serialnumberofthetransmitter

erchangetransmittertuningunitswith

s.

rkeddecreaseinthelifeofthetrans-

tsfromoverorunder voltageappliedtothe

entvoltagefrequentlyandadjust,if

nparagraph23.

ngingthefrequencybandofthereceiver

ANDCHANGEswitchbetweentwo


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ntilit definitelyengagesthedesiredband.

Avoidunduepullingorstressingofthis

fromthereceiverbeforethereceiverpanel

movedfromthecabinet.Atno timeapply

ethepanelandchassisassemblyis being

henthesetisnot beingusedduring

ds,placetheSENDRECswitchinthe

SENDposition,thereis asmallcurrent

trols(figs.2,3,5,7,and8).Trans-

rcontrolledbythefollowing:

-A(SCR-193-A,SCR-193-B,SCR-

-B(SCR-193-D,SCR-193-E).

SCR-193-A,SCR-193-B,SCR-193-C).

phoneT-17connectedtheretoforvoice

5connectedtheretoforc.w.trans-

.

309(SCR-193-B).

connectedtheretoforc.w.trans-

12,BC-312-C.

nda keyandmicrophoneforc.w.

tively,connectedthereto.

onductaudiofrequenciesthroughthe

to controlboxBC-321.

-191-A,BC-191-Corconnectedtoit.

nparagraph17connectedtothe ANT

terminalstrip.Thisstripmaybe installed

.

0to8 ampere,radiofrequencyammeter

catedintheupperright-handcornerof

ndicatesthe currentoutputofthe

etuningdial,markedANTINDTUN-

ytuningthe antenna.Itislocated

tennacurrentammeter.

ch,markedANTCIRCUITSWITCH,

antennacircuitchangesrequiredfortuning


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ETC.25

stypesofantennas.It islocateddirectly

ancetuningdial.

ningdial,markedANTCAPTUNING,

elowtheantennacircuitswitch.This

rtuneacapacitorin theantennacircuit.It

mechanismsothat itsfinalpositionmaybe

switch,markedANTINDSWITCH,P,

riationsin antennainductiveloading.This

h,eachpositioncorrespondingtoastop on

ocatedin thelowerright-handcomerof

witchmarkedCWFILandMODFIL

ntennacircuitswitch.Itisused totransfer

modulatortubefilamentsor tothemaster

ifierfilaments.

witchlocatedtothe leftofthefilament

voltmetermarkedFILVOLTAGE

ansmitterOFFONswitch.Thismeter

ageofthemodulatortubes,ormasteroscil-

ascontrolledbythe filamentvoltmeter

ve.

directcurrentammetermarkedTOTAL

eleftofthe filamentvoltmeter.This

urrentdrawnbythe radiotransmitterand

catingresonancewhiletuning.

a pointerforindicatingTONECW

vely.Thisswitchislocatedtotheleftof

hetransmitterwhiletuningadjust-

key islocatedintheleft centerofthe

nitsTU-5-AandTU-6-A.

dchangeswitchlocatedinthe lowerleft-

ttertuningunit. ItismarkedBAND

susedforthe circuitchangesnecessary

ndused.

ningcontrollocatedin theupperleft-

rtuning unit.Itis markedMOTUNING,

mechanismsandalock.Thedialmechanism

cyalsoactsas avernierandisdivided into

yexposedscaletothe leftofthedial lock


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teshundreds,whilethe so-culledvernier

ingcontrollocatedinthe upperright-

rtuning unit.Itis markedPATUNING,

uneacapacitorinthe tankcircuitofthe

vdedwitha locktoholditsfinal setting.

witchlocatedinthelower right-hand

ngunit. Itisa 6-positionswitchmarked

D.Thiscouplingswitchselectsdiffer-

ouplingcoil.

etransmitterand theotheronthe tuning

d,namelytheneutralizingcapacitorand

citor.Accessmaybehadtotheneutralizing

chanismuponremovalofthecalibration

libration-resetcapacitormaybehadthrough

he testkey.Thesecontrolsarenot

operationofthetransmitterbutmaybe

escribedinparagraph35.

mittermaybeoperatedforc.w.,tone,or

ases,adjustthetransmitterinitiallyjor c.w.

ttershouldbeapproximatelytunedbefore

)Headparagraphs23and24.

FONswitchto theOFFposition.

rand lockinplacethetransmitter

eassignedfrequency.

ngfor theassignedfrequencyfromthe

ntofthe transmittertuningunit.If

sbetweenanytwotabulatedfrequencies,

setting.

SWITCH,A,theMOTUNING

NGcontrol,C,to thenumbersindicated

ppositethe correctfrequencyonthecali-

SWITCH,D,on1.

CEswitchonthe CWposition.

eyin anyjackmarkedKEY.

chonthereceiverpaneltothe SEND

insertedintheMICjackof controlbox

radiocontrolboxBC-309,turnthe

oxestothe ONposition.

FFONswitchtothe ONposition.The

dthemasteroscillatorandpoweramplifier


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ETC.25

hetransmittingkey.

ercircuitto resonancebyvaryingthe

minimumtotalplatecurrentis indicated.

ytuned,the totalplatecurrentwillbe from

WITCH,N,in position4forfre-

nd2500kc.,orinposition 3forfrequencies

c.

CH,P,inposition1.

INGcontrol,M,formaximum

edbytheANTCURRENTmeter.Ifthe

esonance,placetheANTIND SWITCH

mberedpositions,andretunetheANTIND

onanceisobtained.

nnaasabove,theTOTALPLCUR-

n200 milliamperes,thecouplingtothe

dbyplacingtheANTCOUPLINGSWITCH,

pointandtheantennacircuitretunedas

allyadjusted,thetotalplatecurrent

iamperes.

ustment.Havingcompletedthepro-

ve

platecurrentwhenthetransmitteris

FFONswitchtothe OFFposition.

CEswitchontheVOICEposition.

FFONswitchtothe ONposition.

catedtotheleftcenterofthe trans-

currentindicatedon theTOTALPL

lplatecurrentmetershouldnowread

an thecurrentnotedin(a) above,asthe

rawingabout20ma.(Onesmall scale

URRENTmeterisequivalenttoa 20

entthatthecurrentchangeis greateror

trollabeledMODBIASwillneedadjust-

ntrolissocalibratedthatthe current

besis inverselyproportionaltothesetting

tedbyusing ascrewdriverinsertedin

atedjustto theleftofthe MODBIAS

ththeadjustmentasfollows:


partmentshield.


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ps,andtheprocedureindicatedin (a)

otatetheMODBIAScontrolin adirection

torplatecurrenttothevalueindicatedin

ularbatteryvoltagewillcauseachange

rawnonc.w.,andfrequentcheckingofthe

on c.w.duringtheprogressof theabove

WiththeadjustmentoftheMODBIAS

ustmentoftheINPUTLEVELcontrolis

entwill requiretheuseofan additional

andreceivetransmissionsinthefrequency

-193-A.Thisadditionalradiosetshould

stanceand/oroperatedwitha reduced

atthereceivercircuitsarenotoverloaded

hetransmissionsfromtheSCR-193-A.

plishedasfollows:

191-AOFFONswitchinthe OFF

microphoneintheMICROjack.

tchlocatedonthe receiverpaneltothe

ocatedon thereceiverpanelinthe

artmentshieldandusinga screwdriver

gdevicelocatedtotheleftofthe INPUT

hedial at1.

ONswitchto theONposition.

nebutton,andusingastandardspeech

onductatransmissiontothedistant radio

(Thesetransmissionsshouldbeofabout

n orderthatthedistantoperatormay

eechtransmission.)

nalstrengthanddegreeof modulation.

ps,rotatetheINPUTLEVELcontrol

ons,bytheproceduredirectedin(a) to(i),

istantstationmakesareport ofindistinct

he INPUTLEVELcontrolsomewhat

e distantstation.Thetransmissions

stinct.


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ETC.25-26

platecurrentduringthetransmission

isshouldneverexceed300ma.Under

tions,itwillbenecessarytoset theINPUT

werpointthanthat arrivedatin(k)

hlevelto themicrophoneuntilthecurrent

hespeechleveltothe microphoneis

voicewiththemicrophonetouchingthe

ELcontroltoohighresults inover-

transmissions,abnormallywidesidebands

aseininterferenceonadjacentchannels,

ces,blowingoffuses,anddamagetothe

avingcompletedtheproceduredirected


CEswitchonthe TONEposition.

FFONswitchtothe ONposition.

beeffectedbyusingthe microphone

orTESTKEY.Thetotalplate current

0and350 milliamperes.

Themagnitudeoftransmittersidetone

uitofthe radioreceiverisadjustedby

trol,markedSIDETONE,locatedinthe

g.3.)Inthejunctionbox TM-188,

C,thereislocateda potentiometerRS-218

naladjustmentofthesidetone.

ols(figs.5and7).Receptionisaccom-

efollowing:

,BC-312-Corconnectedtoit

tedontheleft centerofthefront

NGE.Eachpositionismarkedwiththe

cyclesofthebandthroughwhichthere-

par.31.)The BANDCHANGEswitch

atein frontofthemaintuningdial.

diallocatedinthe upperleftofthefront

eflectorandmarkedFREQUENCY.

tricscales,theoutersix ofwhicharecali-

y.Thefirstorinner scaleiscalibratedin

5forreadypositionreference.Themasking

ovecoversthefrequencyscalesnotinactive

scale andthatpertainingtothefrequency

DCHANGEswitchmayberead.


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t centerofthefrontpanelmarked

R,respectively.TheFASTTUNING

ningdialat areductionratioof25 to1.

esthemaintuningdialat areduction

onof100equal divisionsaroundtheperiph-

permitsinterpolationofthe Inner0to

gdial.TheVERNIERcontrolmakesone

ovethemaintuningdialone graduationon

ontroltotheleftof themaintuningdial

therightofthe maintuningdial

G.Anarrowonthe controlwhenthe

Tmarkingonthepanelindicatesthatthe

eceivercircuit.Otherpositionsofthearrow

eris inthecircuit.(Seepar.31 andfig.

rightoftheCRYSTALPHASING

ndhas100 equaldivisionsmarkedonits

nreference.Anarrowmarkingonthe

tionofrotationforincreasingvolume.This

uallychangingthevolumewhentheOFF

rthe MVCorAVCposition.

hmarkedCWOSCOFFONlocated

trol.

rollocatedinthe upperright-hand

e lowerrightofthefront panelmarked

ely,foreachposition.Whenthearrow on

oweris removedfromthereceiver.When

veristurnedonandmanualvolumecon-

ded.WhenitpointstoAVC,thereceiver

cvolumecontrolofthereceiverisprovided.

detailedmannerinwhichtheOFFMVC

tlyfunction.

hinthe lowerrightofthefront panel

olslocatedbelowtheBANDCHANGE

JUSTandNOISEBALANCE,respec-

hlocatedintheright centerofthefront

OFFON(radioreceiverBC-312only).


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ETC.26

rkedFUSEontheir screwcapsand

PARE,respectively,fortheBC-312,

SPARE,respectively,fortheBC-312-C,

below.Beingidentical,thefusescontained

interchangeable.

NOISEANT,GND,respectively,

e panelandALTSIGANTin theupper

ontpanelin radioreceiverBC-312.In

woterminalsaremarkedSIGANT,one

Theyareall locatedalongtheleftside

MICRO,SPEAKER2NDAUDIO,

PHONES1STAUDIO,respectively,

dgeof thefrontpanel.Thesejacksare

fplugs forakey,microphone,loudspeaker,

vely.

catedonthefrontpanel.Powerfor the

hacordplug whichisinsertedintothissocket.

ocketto theinteriorofthereceiverare

ngfourscrewsofaprotectivemetalcover

ovingthecover.

nnectingtheantennaterminalstothe

minalof thetransmitterwhenthelatter

nna,if used,isconnectedtotheNOISE

ndingthereceiverchassistothechassisof

otheGND terminal.

321.

ebottommarkedPHONENO.1and

ybeinserted plugsfortwoheadsetsfor

nthefront platemarkedVOLUME

,respectively,forcontrollingthevolume

n(a) above.

vermaybeoperatedforc.w.,toneorvoice

controlledmanuallyalone,ormanuallyand

electivitymaybecontrolledbytheuseofthe

)Readparagraphs23and24.

gaboveaveragefrequencystability,

Nswitch(BC-312only)totheON

priortooperation.


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sP-19 inPHONES2NDAUDIO

Ojackofthereceiver;inPHONENO.

ofthe controlboxBC-321,ifused.In-

fused,in SPEAKER2NDAUDIOjack.

switchtothepositionwhichcovers

ONswitchto theONposition.

ASINGcontroltotheOUTposition.

tchto theREGpositionifthe receiver

withthetransmitter.

Yormaintuningdial'bymeansof

ntiltheassignedfrequencyisindicated

controlswitchtothe MVCposition.

manuallycontrolledwhentheswitchisin

meinwhichthe receiver"warmsup",

ntroluntilmaximumnoiseis heardinthe

lightlyoff frequency,usetheVERNIER

w.,tone,or voicesignalsontheassigned

istinguished.Itmaybenecessarytotune

nedfrequencyuntilthedesiredsignalis

eALIGNINPUTcontrol.

maynowbefurtheradjustedto adesired

Tcontrol.Theuse oftheCWOSC

,000cyclevariationintheresultant beat

tdoesnotchangethefrequencyadjustment

er.

erotatedat anystageofthetuningto

oa desiredlevel.Anincreaseinvolume

fthereceiver.Intuning thereceiver

maintainthevolumefairlyhigh.Volume

UMECONTROLNO.1orNO.2on the

tteris used.

tyofthe receiver,ifdesired,maynowbe

edin(4)below.Itis inadvisabletoemploy

whenreceivingc.w.ortonesignals.

ption.Usethesameprocedureasprescribed

ve)exceptplacetheCWOSCOFFON

ssoon asthesignalis tunedin.

control.MovetheOFFMVCAVC

Whilethisreducesthe sensitivityofthe


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TC.26-27

inthe outputataconstantlevel asdeter-

setting.Automaticvolumecontrolis

esignalfluctuatesorotherwisetendsto vary

yorrejection ofinterferingsignal.Rota-

NGcontrolfrom theOUTpositionina

nincreasestheselectivityofthereceiver.

controlwillpermit ofrejectingorminimiz-

anadjacentchannelwithoutserious

signal.Maximumselectivityis,ingeneral,

kgroundnoise,andusuallyisestablished

STALPHASINGcontrol isinthe vertical

s intendedprimarilyforuseinthe recep-

stocut offthesidebandsofvoicetrans-

onhowfartheCRYSTALPHASING

uentlyeliminatesinterferenceonadjacent

ngtheactualintelligibilityofthe voice

bedeterminedbytrial.

ninterferenceon the1,500-8,000kc.

lowtheprocedureprescribedin6(1)above,

the twofrequencybands.

nnato theSIGANTterminal.Discon-

henoiseantennaconsists ofapieceof

etweenthesourceofinterferenceandthe

receiver.)AdjusttheNOISEADJUST

mnoiseoutput.

ntenna.Connectthenoise antennato

djustthe NOISEBALANCEcontrol

output.Thenoiseoutputshouldbe equal

e.Ifthenoiseoutputs arenotequal,re-

e noiseantennauntiltheyareequal,and

CEcontrolfor maximumnoiseoutput.

s.AdjustbothNOISEADJUST and

ntiltheminimumnoiseoutput is

satisfactory,itmaybenecessarytomove

seantennaanumberoftimes,repeatingthe

euntilthebest resultsareobtained.

a.Inspections.Toinsureunin-

thevariouscomponentsofeachinstallation

soperation.Makeathoroughinspection

ery50hours ofoperation.Forinspection

h33.


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timeswhenthereceiver,transmitter,or

actualoperation,placecoversBG-75,

esecomponents,respectively.Closeall

astenboxesandcasescontainingthe

n use,sparetubes,andotheraccessories

sets,keys,andmicrophones-whennotin

e.Theantennamayormaynot bedis-

itsprospectiveuse.Ifitis disassembled,

mpartmentsofrollBG-56and placethe

ewaboltprovidedforthepurposein the

trapcoverBG-67overthewhole.To

r vibrationofthevehiclewheninmotion,

hesesetswhicharenot otherwiseprotected.

radiosetSCR-193-D.

ectsradiosetSCR-193-E.

ntsofthesesetswillbe lubricated

outlinedinparagraph34.

Seeparagraph35.

r.Wherethereisa likelihoodofexposure

verthesecomponentsasinb above.These

coverson.Slide fastenersonthecovers

tterareopenedand thefrontflapsheldup

sduringoperation.

not equippedforoperationwiththe

ace.

etsareto remainoutofservicebut

ethana fewdays,proceedasdirectedin

bletheantennaandcovertheendsof the

umjellybeforeplacinginroll BG-56.

beremovedfromthevehicleandstored

arefully,coverorwrapsecurelyagainstdust,

cation,andsafeguardagainstaccidental

ordust,rust,orinjury, andcleanand

FPARTS

1-AandBC-191-C,andtransmittertuning

9

andBD-77-B30

ndBC-312-C31

-191-AandBC-191-C,andtrans-

andTU-6-A.Thetransmitter,


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ETC.29

ransmittertuning units,containsthe

one,orvoicetransmission.Withtrans-

hetransmittercoversafrequencyrange

ransmittertuning unitTU-6-A,itcovers

kc.Duringtheexplanationofthedetailed

tter,itwillbe assumedthattransmitter

used.

rcuitsofradiotransmittersBC-191-A

racticalpurposesidentical.Theradio-

masteroscillator,poweramplifiertype.

uitconsistsofapush-pullmodulatorwhichis

er.Thetransmitterutilizes atubeVT-4-C

^t-Cforthe poweramplifier,twotubes

modulator,anda tubeVT-25forthe

mplifier).(Seefigs.17,18,and19.)

ythemasteroscillator,poweramplifier,

soperate.Fortoneandvoicetransmission,

eramplifieroperatesClassC;the modu-

rateClassB; theaudioamplifierdriver

ficientaudio-frequencypowerisobtained

orplatemodulationofthe poweramplifier

n).Sidetoneformonitoringpurposesis

mthespeechamplifierduring c.w.,tone,

masteroscillatorcircuitisschematically

oscillatorycircuitbywhichthefrequency

ledis containedinthetransmittertuning

ecasemaybe. Whenthetransmitter

oyedandthe BANDCHANGESWITCH,

theoscillatorycircuitcomprisesthetapped

pacitor607.Movingthe BANDCHANGE

sthefixed capacitors603and613in

apacitor607andenablesthis tuningunit

f itsfrequencyband.Continuousadjust-

mplishedbymeansofthevariablecapacitor

ntrols,coil,andcapacitorsoftransmitter

are arrangedforsimilaroperationon

lowerinfrequencythanthoseobtained

tTU-6-A.Ineachtuningunit, bothcoil

llycompensatedtoreducefrequencyvaria-

ambienttemperature.Subsequentdis-

atorcircuitislimited tothecircuitshownin

entransmittertuningunit TU-6-Ais


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CR-193-AandSCK-193-C,schematicdiagram.


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ETC.

CR-193-AandSCR-193-C,schematicdiagramContinued.


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K-B,schematicdiagram.


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ETC.

R-193-B,schematicdiagramContinued.


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SCR-103-DandBCK-193-E,schematicdiagram.


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TC.


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ANDCHANGESWITCHonposition2.

geacrossthelowerhalfofthecoil601 pro-

rgrid-excitationvoltage.Thecoilisalso

tuningunitTU-5-A,schematicdiagram.

fturns oneithersideofthe centertap.

xcitationvoltageisfurnishedthrough

r-oscillatorgrid-excitationvoltageis

?,A

"*

ertuningunitTU-6-A,schematicdiagram.

or610,whichblockstheplatevoltageoffthe

andchoke1184in parallelareconnected

emaster-oscillatortubetopreventthe


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TC.

illations.Theplatevoltageforthemaster-

ngunitthroughradiofrequencychoke1106,

5,preventsradiofrequencycurrentfrom

ply.Resistor1109is themaster-oscillator

erequiredoperatingbias forthemaster-

tifiedgridcurrent.Capacitor1108is a

apacitor.Gridchoke611,inconjunction

asthe necessaryd.c.pathfromthegrid to

atthesametimea highimpedancetothe

tation.Capacitor1104isthe calibration

oscillatorfrequencycanbeadjustedto


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onwhenevertheoscillatortubeischanged.

hroughasmall portinthefront paneltothe

pacitor1103isasealedcapacitorwhich

ermalcompensationforanyfrequencydrift

ngupandvariationofthe ambienttempera-

Thepoweramplifiercircuitissche-

junctionwiththemasteroscillatorcircuit

plifierplate tankcircuit,bymeansof

anceisadjusted,is containedintransmitter

A,asthe casemaybe.Whenthe

6-Aisemployed,andtheBAND

osition2 (fig.21),theplatetank

edcoil621andvariablecapacitor627.

ESWITCHtoposition1placesthe

llelwiththe variablecapacitor627and

coverthelowerfrequencyrangeofthe

equencyadjustmentoftheplatetank

meansofthevariablecapacitor627,con-

apacitorsoftransmittertuningunit

edforsimilar operationonfourbands,

equencythanthoseobtainedwithtrans-

Subsequentdiscussionofthepower

othe circuitshowninfigure22,which

ertuningunitTU-6-Ais usedandisset

WITCHonposition2.Thepower-

itationthroughcapacitor609fromthe

.Capacitor609alsoisolatesthemaster-

efromthepower-amplifiergrid.The

sobtainedfromtheflowof rectifiedgrid

14,1112,1113,and1114.Choke608

epathforthed.c.gridcurrentbut ahigh-

equency.Platevoltageforthepower

hthemodulationtransformer1164,the

etankcoil 621.Thecapacitor1117,in

oil1118,preventsr.f.currentsfromflowing

neutralizingcapacitor612formsa part

gthepower-amplifiergrid-platecapaci-

uitbymeansofcapacitor612prevents

eramplifieronits grid-inputcircuit,thus

ofself-oscillationoftheamplifier.All

eproperlyneutralizedatthe timeof

everrequireadjustmentinserviceunless


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ETC.

disturbed.Thepoweramplifierisinduc-

nacircuitbymeansof atappedinductor

selectedbyapanel-controlled,tapped

onhicouplingisprovidedto allow

eof antennaresistances.

odulatingvoltageisappliedtotheplate

erbymeansof themodulationtransformer


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s1161and1162are operatedinapush-

they arebiasednearlytocut-off.The

xcitationfromthespeechamplifiertube

VWWriVAYW 1

etransformer1157.Thesecondaryof

byresistors 1181toreducetheeffective

emodulatorgridcurrent.Platepower


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ETC.29

obtainedfromthe positivehighvoltage

hlimitsit tothepropervalue.Capacitor

requencybypassforthispowersource..

itoringthetransmittedsignalis provided

interstagetransformer1157.Switch

pon thistransformerwindingtogivethe

peration.(1)TheTONECWVOICE

estoselectthe desiredtypeoftransmission.

nctions:

orfilaments.

ensatingsectionofthefilamentresistor

llatorfeed-backcircuit.

onecircuittothe inputtransformer

eTONEposition(fig.23),capacitor

espeechamplifierplateto itsgridin the

useoscillationatan audiorate,andthus

sgenerated.Thesecondariesofinput

rstagetransformer1157areresonatedby

,respectively,toprovidetherequiredtuned

atecircuitsofthea.f. oscillator(speech-

ningofthesecircuitsis suchastoestablish

ofabout1,000c.p. s.Eesistor1151onthe

er1149servestostabilize thegridexcita-

ertube.Themodulatortubesreceivetheir

er1157.

24), switch1141shutsoffthemodulator

mentpower.Thespeechamplifierfunc-

operation,althoughitfurnishesonlythe

monitoringthec.w.transmission.

.25),switch1141disconnectsthetone

d1180,connectsthemicrophonecircuit

ttransformer1149,andmakesthemodu-

nnectingtheirfilamentstothe supply.

nputlevelcontrol.Thespeechamplifier

ionfromthemicrophonebymeansof

hetransmissionismonitoredthroughthe

themodulatortubesisobtainedfrom

thespeechamplifierfromresistor1114

rma partofthepower-amplifiergrid


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emresultingfromtherectifiedgrid current

pacitors1144and1160serveto bypass

modulatorbias,respectively,ataudiofre-

orbiascontrol(labeledMODBIAS),

ontrol(labeledS.A.BIAS),are accessible

Thespeech-amplifiergridbiasisusually


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TC.

mittersBC-191-AandBC-191-C,functionaldiagramoflow-voltageandcontrol

L'N"1

O191-AandBC-191-C,functionaldiagramofantennatuning


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anufacture,anditsvalueisnotparticularly

ransmitter(fig.22)is controlledby

eendof whichisconnectedtothenegative

rcuitreturns,andtheotherendto fila-

Thekeyingcontactsofrelay1165 are

stor.Whenthekeyingcontactsareopen,

biasedbeyondcutoff,andoscillationis

ngcontactsareclosed,resistor1115is

aseson alltubesarereestablished.Oper-

tsisaccomplishedbysupplyingpower

elay1165.(Seefig.26.) Powerissupplied

,testkey,orthemicrophonekeyingbutton

rationoftheantennaswitchingrelay

ditionalfunctions:

erfromtheantennaandgroundsthe

ertotheantennacircuit.

uit.

ransmitterissodesignedthatit maybe

cein connectionwithapower-supplyunit

erectifierforplatesupply,a low-voltage

s,anda transformertofurnisha.c.

Cswitch1136-1137(figs.3,17,and 26)

estoallowthetransmitterto beoperated

. c.positionthefilamentcircuitis

lcircuit,andthenormallygroundedside

ctedfromground.Capacitors1107(fig.

the tubefilamentsatgroundpotential

encycurrents.Undertheconditionof

tor1138is usedtoadjustthefilament

dicatedbythered.lineon voltmeter1133.

risconnectedtothepowersource.One

forthe adjustmentofthefilamentsofthe

onand theothersideforthe modulator

short outasectionofthe c.w.filament

h1141((b), fig.26)tocompensateforthe

occurswhenthemodulatorfilamentsare

makesitnecessarytoreadjustthevoltages

totoneor voice.Aportionoftheresistor

he12V 14.2Bswitch1139,1140(figs.3

ctfilamentvoltagemaybeappliedboth

oragebatteryisbeingchargedandwhen


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ETC.29

1135connectsfilamentvoltmeter1133

latorfilaments.Ifthefilamentsareoper-

sistor 1138servessimplyasa compensating

edfor readjustingthefilamentrheostat

tomodulatedtransmission.

ent. (1)Theantennatuningequipment

leof tuningpracticallyanyantennato

00to4,500kc.Inductiveandcapacitive

alleltuningare provided.Theselectionof

dits subsequenttuningarereadilyaccom-

heantennacurrentmeterand thetotal

ttermeterbyits sharpdipatresonance

epointofresonance.Inthecaseof the

cribedherein,theantennaiscomprisedof

ennamastsectionsMP-49toMP-53,

henoperatedonafrequencybetween1,500

osteffectivelywithinductiveseriestuning.

d tuningdesiredareselectedbymeans

catedontheright frontofthetransmitter

CURRENTistheradio frequency

esther.f.currentsin thevariousnetworks

uipment.

D TUNING,M,isthecontrolfor the

dinginductor1167,andissocalibratedthat

proportionaltothedial reading.

TCIRCUITSWITCH,N,isthecontrol

eof thefourantennatuningnetworksis

ositionsontheswitchcorrespondtothe

ure27.

APTUNING,O,is thecontrolby

tor1169isvaried,and issocalibratedthat

oportionaltothedial readings.

TINDSWITCH,P,is thecontrolfor

andis soconstructedthatthehigher

spondtothegreatestamountofincluded

COUPLINGSWITCH,D,629(fig.

ttertuningunit isthecontrolforthe antenna

ttertuningunit andisusedto controlthe

mplifiercircuitstotheantennatuning equip-

constructedthatthepercentageofcou-

numberoftheswitchposition.


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works(fig.27)are selectedandadjusted

D(2X/)above)at1beforebeginningany

s.

osition1,thetransmitterworksin to

thehigh voltagebuiltupacrossthe

susedto"voltagefeed"theantenna.This

high frequenciesandfairlylongantennas

ngthestandardvehicularantennas.The

ntainedatresonancebymeansofcontrol

theantennaisvariedbymeansof the

sindicatedbyth.eANTCURRENTmeter.

cuitisadjustedbythecontrolD andshould

estep-by-steptuningprocedureisas

omearbitraryscalereading.

by meansofthecontrolMfor a

ntennacurrentmeter.

edsothattheantennacurrentreads

das in2above.

epeateduntilthe properpower

edonthetotal platecurrent

c.w.).Underthesamecondi-

d,the'lowerthe dialreading

owerthereadingonthe antenna

owerwillactuallybedelivered

tion2,thetransmitterworksintoa

eantennais"currentfed."Theantenna

nsofcontrolsM andO.Resonanceis

eadingontheANTCURRENTmeter.

yfor operationnearthefundamental

ndthereforeisnot particularlyefficientfor

ularantenna.Whenthistuningnetwork

pacityshouldbethe maximumforwhich

efoundthatwill giveresonance.(This

ncevalue.)

on3,thetransmitterworksin toaseries

"currentfeed"andinductiveloading.

rationbelowthefundamentalfrequencyof

yused whentuningthestandardantenna,


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ETC.29

quencyassignmentsfortheseinstallations.

sonatedby meansofthecon-

rcontrolledbyM.

bythedipin thetotalplatecurrent

ntonthe antennacircuitmeter.

e,thetransmitterisloadedbyad-

properplate currentisindi-

rentmeter (200to220ma.

osition4,theantennacircuitis identical

on3 exceptthatanadditionalinductor

serieswiththevariableinductor1167.

e operatingfrequencyisrelativelyfar

equencyoftheantenna,aswillbethe case

ndthestandardantennaareoperatedon

1,500kc.andsomewhatabove.Theadjust-

omplishedasfollows:

ted throughitslimits,whilethe

watchedforany indicationofa

sonanceisfound,thetrans-

pervalue.

efoundat thissettingofP,succes-

values,andrepeatthe variation

onof Puntilresonanceisfound.

circuitconstants,asa resultoftuning,

tofthe poweramplifier.Thisnecessitates

plifier.The tuningofanantennais not

mplifierandantennacircuitsareboth

erfrequency.Undersomeconditions

ossibletoresonateanantennaon either

.Operationonposition3of controlN

oice.

8).RadiocontrolboxBC-309provides

smitteroffand onandforconnectingthe

parallelsidenticalcontrolsonthetrans-

1maybeusedtoturn thetransmitter

tthemicrophone.Italsoparallelsidentical

rproper.Remoteoperationofthetrans-

hedatthelocationofthesecontrolboxes.

contains,inadditiontotheOFFON

03,apilot light1304,andasocket1301.


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ns,inadditiontotheOFFONswitch

twoheadsetjacksandtwopotentiometers,

olforthetwoheadsets.Theconnection

nals10and 13oftheterminalboxto the

esaudiooutputfromthereceiverto the

7-AandBD-77-B(fig.9).a.Dyna-

D-77-Bprovidethehighvoltageplate

rsBC-191-AandBC-191-C,respectively.

torontopof whichismountedtherelay

rtingrelay,fuses,andfilter elements.

40amperesinput,1,000volts0.35

p.m. with55 C.rise,forone-halfhour

otorsBD-77-AandBD-77-Baresub-

nalappearancesandmountingdetails,

ervativelyratedatthevaluesgivenabove

ublearmaturewindingconsistingof a

or)windingandahigh-voltage(1,000-volt

windingterminatesatacommutatoron

Thewindingsare carefullyinsulated

s commontobothmotorandgenerator

mthe12-voltstoragebattery supply.

cketsoneachendaffordmaximumaccessi-

ndbrushes.Theexternalleadsof the

otherelayfusebox throughtwobushings

ame.

(fig.10)ismounteda moldedterminal

ardaremountedthe startingrelay,

agefuses,andtheelementsofthefilter

olenoidtypestartingrelayis used.A

parefuselink,anda socketwrenchare

coveroftherelayfusebox.In oneendof

untedsocketsSO-39andSO-41.A%-inch

eofaconduitcontainingthetwo powerinput

thesesockets.

2andBC-312-C.Radioreceivers

practicallyidenticalandareofthemulti-

eterodynetype,andemploymetaltubes

rencesarepointedout asvariouselements

d.Unlessspecificallyreferredtoa particu-

ssionhereinappliesequallyto each.Pro-

eptionofc.w.,tone,orvoicesignalsoverthe

o18,000kc.,insix stepsasfollows:


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ETC.

e28isafunctionalcircuitdiagramof

wingtheconnectionssetupbytheband

signalin oneparticularfrequencyband.

thebandchangeswitchitself,and allcoils

altotheoperationon thatband,are

plicity.RadioreceiversBC-312and

gesofpentoderadiofrequencyamplifica-

separatetrioderadio frequencyoscillator,

rmediatefrequencyamplification,aduo-

msthefunctionsofadiodedetectorand

cyamplification,andaseparatestageof

amplification.Theseparatetriodeoscillator

at noteforc.w.reception.Theantenna

desameansof transferringthedesired

quencystage,andalsoprovidesameansof

hefirst stageonbandsAand Bphasedin

al noiseismateriallyreducedbelowthat

antenna.Thetworadio frequencystages

oacttoreducepossibleinterferencefrom

theintermediatefrequencyoratthe so-

gefrequency.Themixertubecircuitwith

dstotheselectivityofthe receiver,andalso

thesignalfromthefrequencyreceivedto

atefrequencyamplifieristuned.The

tagesprovideadditionalselectivityandgain.

edemodulatestheamplifiedsignaltoaudi-

ystagesprovideadditionalamplification.

ingatafrequencyslightlydifferentfrom

atefrequencystagesaretuned,,provides

adjustableinpitchwhenreceiving-c.w.


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ETC.31

8and31).Theantennacircuitiscoupled

adiofrequencystage(Li)throughcapac-

are inductancesaddedtothecircuitto

ygeneratednoisenormallyreceivedonthe

,coilLJ?servesas aradiofrequencychoke

ground.Thefunctioningofthisnoise sup-

dindetailin kbelow.CapacitorC26,con-

frontpanelmarkedALIGNINPUT,in

inconnectionsofL25,L^,andL27produced

,permitstuningtheantennacircuitto

signal.LM^isa neonlampwhichnormally

Whena certainthresholdvoltageis

mesaconductorbyionizationandprevents

assingthecurrentto ground.Itisused

ereceiverfromanyexcessivevoltages

he antenna.

).Thecircuitsofthefirstradiofre-

uency,andmixerstagesareverynearly

gnedtopermittuning withasingle

escreenvoltagesforthefirstradio

requency,andmixertubesareprovidedby

edbetweenplusplatevoltageandground.

dR48,Ri6,andRSOformthesevoltagedividers.

sedtoground acrossthesevoltagedividers

ndC49,respectively.Cathodebiasforthe

econdradiofrequencytubesispartly fixed

edportionofthis biasissecuredbythe

pectively,andfromthejunctionof these

s atthevoltagedividerformedbyRsaand

35isshortedto groundforautomatic

erationandinthis modeofoperationthe

besaresecuredentirelyby thedropacross

sof themixertubeis securedbythedrop

dreturnis throughresistorR13.C^,

toground acrossthecathodebiasingresistors.

voltagesfromtheprecedingtubesfrom

econdradiofrequencyandmixertubes,

stradiofrequencystageis usedtomake

eidenticalwiththoseofthetwo succeeding

uning referredtoabove.LI,L7,andLj3

fthegrid circuitsofthefirstradio fre-

uency,andmixerstages,.respectively.The

diofrequencyandsecondradiofrequency


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upledtothetankinductancesofthenext

etankinductancesaretunedbyagang

8,CM,andCM-Inserieswith thesectionsof

eecapacitors,C25,Cioo,andC38,acrosswhich

tchSW2,SW4,and SW8(operatingwiththe

).Thisgangcontrolswitchpermitsthese

din thethreehigherfrequencybandsto

yspreadonthedial, andshortsthesecapa-

equencybands.TrimmercapacitorsCi,

o permitindividualpreadjustment(aline-

nvolvedto resonanceatagiven-input

gofthegangtuning capacitor.C32andC39

ypasscapacitorsandinconjunctionwith

olatethed.c.plate supplyfromradio

ockingcondensers,theypreventtheshort-

hefirstand secondradiofrequencytubesto

diofrequencystageisplacedinthe circuit

to thoseofthesecondradiofrequencyand

ofgangtuning.C102,C99,and C82actas

c.operation.R4andR53;Rg andRIO;

impedanced.c.gridreturnforthe tubes

apaththrough whicha.v.c.voltagesare

hese threestagesismadethrough

m.v.c.operationandthroughROTandRao

urposeof R30Isexplainedindetail inj

n serieswiththeplateleadsof thetubes

torsC3i,C37,andC54,inconjunctionwith

negligiblevaluetheamountofradiofrequency

wersupplycircuitfromthesetubes.

tor(fig.28).Theradiofrequencyoscillator

ycircuitwiththeplateend ofthetank

potentialforradiofrequencies.Thetank

sistsofinductanceL]9,whichistuned by

e maintuningcapacitorsC28,034;andC^,

usedinthethreehigher frequencybandsto

yspread,butisshorted outbyswitchSW8in

bands.SwitchSW8isgangedwithswitches

atrimmercapacitorwhichadjuststhe

agewiththeother tunablestagesofthe

(seefigs.17,18,and 19),whilenotessential

cillatorcircuit,are includedinthetank

or trackinginallbandswiththose ofthe

rstages.C88servesasa grid-blockingcapac-


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ETC.31

resistor.RuandR togetherserveto

uppliedbythedynamotorto theproper

,and R^aredifferentforthedifferent

eivertoinsurethat theplatevoltageonthe

ctin eachband.Theradiofrequency

oris completedthroughC^andgroundto

requencyvoltageoccurringbetween

ortubeand groundisimpressedonthe

be (1stdetector)throughC47.Theaction

on thereceivedsignalproducesanoutput

esamemodulationas thesignalreceived

ediatefrequencyamplifieristunedto

nd 29).Theoutputofthemixerstageis

gridcircuitofthe firstintermediatefre-

sformerL28.CM,inparallelwiththepri-

ormsaresonantcircuitwhichis tunedto

tionof anironcorewithinthe transformer

transformerandbothcoilsof trans-

nedin asimilarmanner.Inthe gridsideof

bridgecircuit consistingofcapacitorsCM,

X.Thiscrystalis providedwithashorting

chclosed,thesecondaryofL28and

rmaresonantcircuittunedto theinter-

tone-halfoftheavailablevoltageacross

ceL28isimpressedonthegrid ofthefirst

ubethroughblockingcapacitorC62.When

ningthe CRYSTALPHASINGcontrol

esignalis impressedonthegridofthe

cytubethroughcrystalCXandthrough

scuttothe intermediatefrequencyof470

ytunedresonantcircuitand offersahigh

ies,exceptitsresonantfrequency.The

derwouldnormallyserveasa bypasstothis

itsimpedance.Forthisreason,thebridge

itorsC94,C95,andC5ipermitsbalancingout

fthecrystalholder andraisestheimpedance

sotherthanthe resonantfrequency.Any

itorC61providesabypassaroundthe

cuitimpedancetoundesiredsignals.This

eCRYSTALPHASINGcontrolsincethe

ectsoftheholder,behavesasaresonant

voltageverynearlyin phase.Introducing


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ETC.31

sconditionofresonanceandintroducesa

nthecurrentandvoltage,themagnitudeof

edegreeof unbalance.

amplifier(fig.28).ResistorR18provides

urrentgridreturnfor thefirstintermediate

eswithR52providesfor theintroduction

radiofrequencybypasstogroundshunting

a.v. c.circuit.Thecouplingbetween

atefrequencystages,andbetweenthe

uencystageandtheseconddetector,is

rmersL29andL30.Bothsidesofbothof

rcuitswhichareresonanttotheniter-

ecessarycapacitancebeingprovidedby

C85 andC93;C64andC92.C77,C9i,C92,and

2-C.Thenecessarytuningtosecure

oughtheuseofmovableironcoreshi the

rmerL28.Theresistor R19hasthesame

orthefirst andsecondradiofrequency

rthesecondintermediatefrequency

sistorR24.The gridreturnofthe second

ubeisthroughresistorR23,whichprovides

c.voltage,andwithcapacitorC66prevents

ingintothea.v.c. circuit.Thescreen

sareobtainedfrom thevoltagedividers

andR25and R28.Thesescreengridsare

pacitorsCMandC69,respectively.C58and

thodesto ground.

8and30).Aduo-diode-triodeisemployed

diodecircuitactuallyservingforpurposes

rdiodecircuitprovidingfora.v. c.action.

ubeservesasthefirst audiofrequency

functionswillbedescribedin detail

hecathodeandthedetectordiodeplate

erectifiersothatanycurrentflowingthrough

lsating.Anyportionofthedropacross

plifiedasaudio frequency.CnandC72

radiofrequencybypassesacrossthese

epropercathodebiasforthis tubeandis

er(figs.28and30).Thetriodeportion

sas theamplifyingtubeforthefirst stageof

ereceivesitsgridexcitationthrough

ionconsistsofthedropacrosstheentire


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perationandthedropacrossthelower portion

operation.R32servesasahigh impedance

be.Theoutputcircuitofthe firstaudio

tothecontrolgrid ofthesecondaudio

apacitorC76.TheprimaryoftransformerTI

plingelementandalsoas theprimaryofthe

oasecondarycircuitcontainingJi,into

ged..Cy4in thiscircuitpreventsaudio

hepowersupplyandcompletestheaudio

thistube.R33servesas ahighimpedance

condaudiofrequencytube.Thecathode

equencytubeis providedbyR3j,whichis

pacitorC98.Theoutputofthe secondaudio

throughtransformerT2tojackJ2, intowhich

ndtoJ3 (seefigs.17,18,and19), intowhich

ged.In thecaseofthereceiverBC-312-C,

ailableinthe connectionsofthejackJ3for

hesame,providingthespeakeris properly

Cordingdataissupplied withthespeaker.

eventsaudiofrequencyfeedbackintothe

testheaudiofrequencyplatecircuit.

AmodifiedHartleycircuitisemployed

dof thetankcircuitatgroundpotential

nkcircuitofthisoscillatorconsistsof coil

4andC85in parallel.C86isagrid-blocking

returnresistor.The platesupplyofthis

ghswitchSWn(CWOSCONOFFswitch)

oscillatoronor offatwill.R37,in serieswith

esto droptheplatevoltagefromthat supplied

rrectvaluefor thistube.Theradiofre-

pletedthroughcapacitorC8?andground

nof thedropacrosstankcoilL3tis im-

oftheseconddetectortankcircuitthrougha

fCM,C97,R5i,andL32and throughcoupling

eofthisfilteris topreventtheintroduction

cillatorfrequencyintothe detectorcircuit

nualvolumecontrolaction(figs.28and

nmanualvolumecontrol(MVC),the

condradio frequencytubesandthefirst

ubearereturnedtothevoltagedividercon-

s voltagedividerislocatedbetweenplus

sothatchangingthe valueoftheresistorR35


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ETC.31

rolonthefront panelchangesthiscathode

ainofthesetubes.R30is shorted,preventing

2) below.Inthismodeofoperation,that

ncysignalwhichappearsacrossall of

theinputofthefirst audiofrequencytube.

trolaction(figs.28and30@).Forauto-

.c.)operation,resistorR3Sis shortcircuited

encyvoltageavailableatthegrid ofthe

snowthe voltageacrossthatportionofR34

dingcontactofresistorR34.Changing

by operationoftheVOLcontrolonthe

mountofaudiofrequencyvoltageimpressed

cytubewithoutinterferingwitha.v.c.

deplateoftheseconddetectortubeis

rcuitof thesecondintermediatefrequency

6?togeneratethea.v. c.supplyvoltage.

weenthisplateresistorR30 toground,

8tothecathode.Thecathodeis main-

alwith respecttothea.v.c. platebyd.c.

sectionofthetubeflowingthroughR28.

einthisa.v. c.circuitwhenthepeakvalue

edis greaterthanthed.c.drop across

iedvoltagewillappear acrossresistorR30.

geacrossR30is thereforedependentupon

receivedinexcessofthedropacrossresistor

nisobtainedonsignalswhosea.c. peak

pacrossresistorR28.Thistypeof actionis

v.c.In a.v.c.operation,thecontrol

uency,secondradiofrequencymixer,first

andsecondintermediatefrequencyarere-

esistorR30.A changeinthevoltageacross

ctsthebiasandgain ofthesetubes.The

thesetubesmorenegativelyonastrong

gainand tendingtomaintainaconstant

t(figs.28and31).(1)A circuitispro-

ucinginterferenceonbands AandBcaused

gnitionsystems.Threeinductancecoils

whenproperlyadjustedtoreducethis type

pledtoL26,anelectrostaticshieldbeingpro-

ouplingisentirelymagnetic.Thiscoupling

plingbetweenL26andL27is primarily

rymagneticshieldbeingprovidedtoinsure


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CESSHOWN

ICAL

CESSHOWN

CESSHOWN

ENTICAL

C-312.functionaldiagramotantennacircuits.

ssecured.ThecouplingbetweenL26and

nobonthefrontpanelmarkedNOISE

plingbetweenL26and L25andservesto

ntroducedinto thereceivercircuitsfrom

plingbetweenL^andL/2, andcontrolled


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ETC.

rol,determinesthephaserelationofthe

roducedintothereceiver.Thecoupling

ustedto produceminimumnoise(notneces-

riedtoreducethenoiseto zero,thereby

thenoisefedbythe separateantennas

2-C,screwsandlocknutsareusedto

dNOISEADJUSTandNOISEBAL-

Metaltubesoftheheatertypeare em-

-312.Thesetubesrequireaheater voltage

ertube.To permitoperationona12-volt

BC-312andBC-312-C,functionaldiagramoflow-voltagecircuits.

setubesareconnectedinaseries-parallel

eswhichrequirethesameheatercurrent

enthesepairsarrangedin parallel.Tube

78andC79.Actualheaterconnectionsare

d 19.

ntheatercircuit(BC-312only)(fig.32).

diofrequencyoscillatorataconstant

ngofits tuningcapacitor,theentirecircuit

atedcompartment.Theuseofelectric

maintainsthiscompartmentataconstant

SS,R39,andR^aretheheaterelementsfor


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beingconnectedinparallel andcontrolled

olTHSi.R^iscut outandintothecircuit

S2.Inserieswiththis combinationisthe

FFONswitch)whichpermitstheheater

trolled.C89andC^areconnectedacross

recontrolsTHSjandTHS2,respectively,

usedbytheopeningandclosingofthe

aturecontrolsareadjustedtoopenat

tively.Thesevalueshavebeenselected

it)0 F.ismaintainedwiththeminimum

ontrolcontactbreaks.Ofthetotalheater

voltsinput),33 wattsareused

F.,and49wattsat109 F.andbelow.

esabove109 F.,only33wattsareapplied

dabove111 F.,noheatissupplied.

etemperaturefallsbelow111 F.,33watts

therateof temperaturefalluntil109 F.

9watts areapplied.Afusemarked

hefrontpanel,protectstheheatercircuit.

9 and32.)TwodiallampsLM-27

M3)areconnectedinseriesacrossthe

nneras toreceivecurrentthroughthe

off andonbythe OFFMVCAVCswitch

rBC-312-Cthediallampsareconnected

he OFFMVCAVCswitch.Thefuse

mbolF2)onthefrontpanelprotectsthis

TheSENDRECswitchcontrolsthe

orts theinputnetworkofthereceivers

roundatsuchtimesas theSENDREC

ndthetransmitteriskeyed.Atsuch

areintended,the SENDRECswitchwill

tion.Thepurposeoftherelayshorting

nimumthevoltagesbuiltupin thereceiver

rgysignalsfromthe transmitterareradiated

eiverofthesensitivityoftheBC-312type.

dDM-21-B(figs.33,34,and35).

ratingonaninputvoltageof12to 14

saryplatevoltageforthereceiverBC-312.

totheundersideof thechassisofthe

onditions,thedynamotorrequires2.7

withanoutputofapproximately82milli-

(Seefig.33.)LIand Ciconstituteafilter


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TC.

of radiofrequencyinterferenceintothe

L2,LS,andL4, togetherwithcapacitors

nitDM-17-A,functionaldiagram.

unitDM-21-B,withfilterunitFL-6-B,schematicdiagram.

acombinationaudiofrequencyandradio

chreducescommutationrippleto avalue


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S

nitDM-17-A,interiorview.

ableandalsopreventsradio frequency

ansmittedbythedynamotortothereceiver

1Bissimilartoandperformsthesame

eiverBC-312-C(fig.34).Underfullload

orrequires3amperesat14volts d.c.,with

y90milliamperesat235volts d.c.A

adiationofradiofrequencyinterference

ycircuit,andalsoactsas acombination

frequencyfiltercircuitwhichreduces

uewhichwillnot beobjectionable,and

ncyinterferencebeingtransmittedbythe

circuits.ThefilterunitFL-6-Bis readily

M-21-B.DynamotorDM-21-Bcannot

A.(Circuitreferencesinthisparagraph

h41.)

iotransmittersBC-191-AandBC-191-C35

e,andvoltagereadings36

ure37


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ETC.32-38

bservedinservicingthisradioequipment.

onlysuchrepairsas areindicatedinpara-

beattemptedonlybycompetentperson-

etestandrepair equipment.Aninex-

emptingtolocateandrepaira minortrouble

ouldserviceinafewmoments,maydamage

xtentas torequireshipmenttoa depotfor

nspection.Thevariouscomponents

CR-193-B,SCR-193-C,SCR-193-D,

nathoroughvisual inspectionbeforeand

toinsurethat thesetisreadyfor useatany

desexaminationofallcordageforproper

Allaccessiblecomponentsareexamined

essary.Attheendofalong periodof

soincludesachecktosee thatthedynamotor

thoroughinspectionofthecomplete

terevery50 hoursofoperation.This

uninterruptedperformanceinthefield.

ectionisas follows:

storagebatteryisatthe properspecific

nggeneratorandregulatorare adjusted

ullycharged.

ddustanddirtfrom allunits,usingan

particularattentionto theloadingcoil,

ompartmentoftheradio transmitter.

em1167,in thiscompartment,andclean

thcarbontetrachlorideandacleancloth.

wheelrunsshouldbetouchedinseveral

resmoothoperation.

urplusofoil dagsuchthatthewheel

omecontaminatedbythelubricant.

ing isinplace,thatall mounting

rigidlyfastened,andthatall nutsand

edwithlockwashersandaretight.

dsare notdamagedandthatallground

fitandsocketsforcompressedpin

havetakenapermanentset canusually

thammerblowattheend ofthepin.


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rtridgefuses areheldtightlyintheir

ouldbe removedandtheclipsbentby

setightly.Cleanclipsandfuseends.

.

efuses byremovalfromthemounting.

surfacesandreplacethefuses.

stemforbrokenor frayedleadsorloose

sulatorclean.Topreventlooseningand

sshouldbe coveredwithrubbertape.Make

venotbeen bentclosetometalworkwhere

htcausesparkovers.

phonesfordefectivecordsanddamaged

ushesforlength.Toinspectthereceiv-

ndDM-21-B,itisnecessarytoremovethe

abinet.Carefullyplacethechassisupside

emovethecoverofthe dynamotorcom-

eningthetwoknurledthumbscrews

ideandthe twoflatheadscrewsonthe

motor.Thebrushholderson boththe

mutatorswillnt>wbeplainlyvisible,and

e removedwithoutemployingtools.Their

bystretchingthehelicalspringsandslowly

thecurvedsectionsofthetwobrush holders

y areengaged.Becarefulnottobreakthe

ons.Ifitisdesiredto withdrawthebrushes

motor,itwillbenecessarytounsolderthe

ebrushholders.Inspectthefaceof each

t least70percentofthe faceofthebrush

commutator.Thebrushfaceshouldshow

hspots.

torcommutatorsforcleanlinessandfor

rarmaturebyhand,andmakecertain

otrubbingagainst thefieldpolesorleads.

enremoved,thearmatureshouldspin freely

ninspection,allplugsand socketsshould

andscreweddowntightly.Alltubesshould

otheircorrespondingsocketsandgrid-cap

made.Chassisshouldbeeffectivelylocked

thelockingcatchesonthefrontpanels.

s.Thevacuumtubesusedinradio receiver


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ETC.33-34

mallyhaveaneffectivelifeof2to3 years.

rformanceofthereceiver,theyshouldbe

tubechecker.Tubesshouldbechecked

endedfieldmaneuversandthosewhichdo

standardsshouldbereplaced.If notube

besshouldbereplacedannually,thereceiver

ormance,andcircuitsrealinedifnecessary.

onshouldbeaccomplishedinaccord-

Donotuse excessiveamountsofoilor

ctricalconnectionstobecomegreasy.Excess

lltendtoworkout ofbearinghousingsand

eitwillcausetrouble;italsomay causethe

esurethatlubricantsandoilholesare

rit,or dirt.Theseabrasivesarethechief

thenecessityfor bearingreplacement.


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TC.


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oradiotransmittersBC-191-Aand

uipment.Thefollowingauxiliaryappa-

justproperlyradiotransmitterBC-191-A.

notissued asacomponentofthesesets

where.

etSCR-211-A.

mmeter(0-1amperefullscale).

aradcondenser,eitherfixedorvariable,

tleast2,500or5,000volts d.c.

torofapproximately10ohms,capable

sistor,andr.f. ammeterareconnectedinseries,

ectedbetweentheantennaandgroundbindingpostsof

dummyantennaloadforthetransmitter.

transmittersBC-191AandBC-191-C

tionbythemanufacturerandnormally

entinthe field.Whennecessary,neutral-

dadjustedasfollows:

FONswitchto theOFFposition.

partmentshield.

plifiertube(VT-4-C)fromitssocket

efilamentpin withapieceofpaperand

etransmitteris turnedon,thepower

otlight.)

tenna(seenoteina above)inseries

mmetertothetransmitter.

CEswitchonCW.

PATUNINGcontrolsforthecenter

cordancewithdataonthe calibration

ingunitTU-5-Aisemployed,or3,750

Aisemployed.)

FONswitchto theONposition.

tto resonanceasprescribedinpara-

sive,usingthe 0-1,r.f.ammeterinthe

etheindicationofresonance.

edPATUNINGuntil the0-1,r.f.

tennacircuitindicatesamaximumcurrent

onchartbyturningthefour knurled

gcapacitorylockbyturning,witha

eleft onequarterturn.


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TC.35-36

gcapacitorycontroluntilthecurrent,

encyammeterinthedummyantenna,is

ntennaandpoweramplifiercircuits

resonance.Iftheammeterin thedummy

edreading,repeattheoperations(8)

ofthe neutralizingcapacitoradjust-

onchart,andrestorethetransmitterfor

ngunitswilleachbe neutralizedwhen

sapproximatelyone-halfengaged.

asadjustment.-Thegridbiasonthe

ansmitterBC-191-Aisadjustedbythe

requiresreadjustmentinthefield.The

Shouldtheinitial settingbecomedis-

ompartment,andsettheS.A.BIAScontrol

calibrationofthetransmittersshouldbe

ployingthefrequencymeterSCR-211-Afor

portantthatthecalibrationbechecked

latortubeischanged.Ifthe checkindicates

morethan25 kilocyclesfromthefrequency

nchart,theoscillatorfrequencyshouldbe

erfor atleast30minutes,withthe an-

ut,prior toadjusting.

erSCR-211-Ato-3000kc.whentrans-

used,or 4500kc.whentransmitter

oroperationon c.w.atafrequencyof

e casemaybe,asprescribedinparagraph

alibrationchartfor thesettingonthe

pproachthissettingfromthelowerdial

setportlocatedto therightoftheTEST

ewdriver,adjustthecalibrationreset

nsmitterzerobeatswith thefrequency

setport.

ance,andvoltagereadings.The

resistance,andvoltagereadingsarefurnished

danceofservicingpersonnel.(Thevalues


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aryslightlywithdifferentsets anddifferent

Thecurrentconsumptionsofthereceiver

atthevehicularstoragebatteryare listed

stedare measuredatthebattery.

dis14.2volts, thevehicularstoragebattery

hicularmotorrunning).

andBC-312-C.

191-AandBC-191-C.

sthe currentandvoltagereadingsat

otorsBD-77-AandBD-77-B forthree

thisequipmentwiththehighvoltage

aboveincludesthattakenbythestarting relay.PublicDomain,Google-digitized

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ETC.

ingsforradio receiversBC-S12and

oltagesshownbelowareprovidedfor the

ofservicingpersonnel.Thereadingsare

ing thesetanalyzeroftestset I-56-A,

volts,theOFFMVCAVCswitchinthe

Lcontrolturnedtomaximum.Forthe

eCWOSCOFFONswitchisin theON

ngsthis switchisinthe OFFposition.

usedwhentheset analyzeroftestset

asurementonthetwor. f.andfirstdetector

pterisinsertedintothetube socketand

he receivergridclip.Thesocketendof

otheset analyzerplug,andthegridclip

dtothe studonthesetanalyzerplug.

adeintheregularmanner.


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sweretakenunderthefollowingconditions,

tbereproducedexactlyif comparison

transmitteraretobe effected.

removedfromthetransmitter.

removed.

witchisseton VOICE.

TU-6-Aisinserted.

the ONposition.

tivemounting.

besockets.Tubesocketconnections,

entsshownbelowaremade,arenumbered

gvacuumtubesocketpinlocations.

rdsockets.Thesocketpinsfromwhich

cetogroundaremadeareidentifiedby num-

Thisfigurerepresentsthecord connecting

ersBC-191-AandBC-191-Casviewed

t.Socketsareeasilyidentifiedbythe

ofthephistherein.Resistancemeasure-

histo groundareindicatedbelow.


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TC.

L-74

ketpinnomenclature.


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ordefectivetubes.Whensetfailureis

shouldbecheckedbeforeinitiatingadetailed

s.Iffailureofbothtransmitterandreceiver

etroubleisusuallyintheprimarypower

thereto.Ifonlyonecomponentfailsto

sible,ifitis r

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TM 11-273 RADIO SETS SCR-193-A,B,C,D,E APRIL 1941

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