RCA AR-77 Manual

CENERAL PURPOSECOMMUNICATION RECEIVERSMODELS AR"77 and AR"77EMI"S)02 D, E, F and G,Manulaclurad byRCA Manufacturing Company, Inc.Camden. N. J.. U. S. A.-A SERVICE OF THE RADIO CORPORATION OF AMERICA-

1GENERAL PURPOSECOMMUNICATION RECEIVERSMODELS AR-77 and AR-77E(MI-8302 D, E, F and G)INSTRUCTIONS\J~ - ~-~Printed in U. S. A.Manufactured byRCA Manufacturing Company, Inc.Camden, N. J., u. S. A."AN RCA SERVICE"lB.31005

MAIN TUNING DIALS TUNINC·S·tJ£TER BAND 5PREAD DIALSVERNIER SCALEVERNIER SCALECRYSTALSELECT1VJTYSWITCHNOISELIMITERCONTROLCRYSTALPHASINGCONTROlTRANSMIT­RECEIVESWITC.HB.F.O.FREQUENCYCONTROLVOLUMECONTROLANDPOWERSWITCHSENSITIVITYCONTROLMA1N ANTENNA RANGE BAND SPREAD TRANSMISSIONTUNING TRIMMER SWITCH TUNING SELECTOR PH-50~~5Figu.re i-General Purpose Communication Receiver(Table Mountinl{ Type) ()2Figure 2-Loud.speaker

TitleTABLE OF CONTENTSPageTechnical Summary 4Description ................................................................................. 6Installation 6Power Supply .............................................. " . . . . . .. . . . . . . . . . . . . . .. . . . . . . 6IiTubes 6Antenna.................................... ............................................ 6Speaker or Phones ........................... ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Rack Panel Mounting of Receiver ... . . . . . . . . . .. ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Rack Panel Mounting of Loudspeaker ... . .. . . . .. ... . . . . .. . . . . . . . . . .. . . .. . . . . .. . . . . . . .. . . . . .. 7Operation ....................................... ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Maintenance ........................................................................ :....-... ' 9Parts List ....................................... . ................................ , . . . . . . . . . . 12FigureILLUSTRATIONS1 General Purpose Communication Receiver (Table Mounting Type) ........................... 22 Loudspeaker .......................................................................... 23 General Purpose Communication Receiver (Chassis Top Views) ............................. 154 General Purpose Communication Receiver (Chassis Bottom View) ..................."........ 165 General Purpose Communication Receiver (Schematic T·601776) ............................. 176 Selectivity Curves (S·851297) ... :....................................................... 187 Fidelity Curves (S·851298) .................. ............................................ 193

--~-,,,-~ --,---,,-----,~-----,GENERAL PURPOSECOMMUNICATION. RECEIVERSMODELS AR-77 and AR-77ETECHNICAL SUMMARYAll performance data were obtained on an average receiver. Slight variations above or below these valuesmay be encountered due to practical manufacturing tolerances. A 300-ohm dummy antenna was used in serieswith the receiver input in making all 'measurements.ELECTRICAL CHARACTERISTICS-Frequency Range (total, 6 bands) ................................................... 540 to 31,000 kcBand 1 ....................................................................... 540 to 1,340 kc·Band 2 ...................................................................... 1,340 to 3,300 kcBand 3 ...................................................................... 3,300 to 5,800 kcBand 4 ..................................................................... 5,800 to 10,200 kcBand 5 .................................................................... 10,200 to 18,000 kcBand 6 .................................................................... 18,000 to 31,000 kcFrequency Stability:Warm-up Shift, 1 minute to 1 hour, 68° F. Ambient (Average Humidity Conditions)..................................................................... Less than 3.5 kc at 30 mcShift with Line Voltage Variation, 105 to 125 volts .................... Less than 1,300 cycles at 29 mcShift is proportionally less at lower frequenciesSensitivity: Input (30% mod.) required for 0.05 watt output ...................... Less than 2 microvoltsSignal-to-Noise and Image Ratios:Band1 ................ {2 ................ {FrequencyKC5401,3401,3403,3003 ................ { ~:!~~4 ................ {1~:~~~5 ........•....... {:~:~~~6 ................ {~~:~~~Microvolts Inputfor 2: 1 Signal-to­Noise RatioImageRatio0.9 ................. 50,0001.7 ................. 3,9001.7 ................. 5,0001.9 ................. 9101.4 ................. .1.2 ................ .1.4 ................ .1.2 ................ .1.8 ................ .1.6 ................ .1.7 ................ .1~ ................ .1,0003205501003808860254

Selectivity .......................................................................... See Figure 6Overall Fidelity (measured across speaker voice coil) ...................................... See Figure 7Maximum Undistorted Output (approximate) ..................... ;......... , ................. 3 wattsPower Supply Requirements:Line Rating~-Model AR·77 ................................................... 105·125 volts, 50/60 cyclesModel AR·77E" .................................. 105-130/140·160/195·250 volts, 50/60 cycles"See "EQUIPMENT" list below for special rack models and optional power packs available.Power Consumption .............................. ~ ................................. .. 70 wattsTUBE COMPLEMENT-R·F and I·F Amplifiers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3 RCA·6SK71st Detector and R· F Oscillator .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 RCA-6K82nd Detector and Noise Limiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 RCA-6H6AV.C. and A·F Amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 RCA·6SQ7Power Amplifier ............................................................... 1 RCA-6F6GBeat·Frequency Oscillator ....................................................... 1 RCA-6S}7Rectifier ...................................................................... 1 RCA·5Y3GVoltage Regulator .............................................................. 1 RCA-VR150MECHANICAL SPECIFICATIONS-Dimensions ....................... 20'/8 inches (width) x lOV2 inches (height) x 11% inches (depth)Weight (net)48 1 / 2 poundsEQUIPMENTModel AR·77: Domestic Model in Cabinet (see "Line Rating") ............................. MI·8302DModel AR·77E: Export Model in Cabinet (see "Line Rating" ) ............................... MI·8302EModel AR·77: Domestic Model in Cabinet (105·125 v., 25 cycles) ............................ MI·8302FModel AR·77: Domestic Model on Standard 10·15/32.inch Panel (see "Line Rating") ........... MI·8302GModel AR·77E: Export Model on Standard 1O·15/32·inch Panel (see "Line Rating") ............ MI·8302HOptional Equipment:Loudspeaker in Styled Cabinet to match Receiver ........................................ MI·8303Loudspeaker on Standard 10·15/32.inch Panel .......................................... MI·8303AExtended Range Loudspeaker in Console Cabinet . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. MI·8314Extended Range Loudspeaker in Wall Type Cabinet ..................................... MI·8314APanel Kit for Rack Mounting of Model AR·77 (12·7/32·inch Panel) ....................... MI·8304Panel Kit for Rack Mounting of Loudspeaker (10·15/32·inch Panel) ...................... MI·8305Power Pack for Model AR·77 or AR·77E (105·125 volts d·c) ............................ MI·8307·2Power Pack for Model AR·77 or AR·77E (210·250 volts d·c) ............................ MI·8307·3Power Pack for Model AR·77 or AR·77E (6·volt battery) ............................. MI·8308Phone Plug ........................................................................ MI·6216Headphones ........... ,............................................................ MI· 5803A·F Coupling Transformer for 500·ohm line ............................................ MI·49045

--~---------~-.-----IL L --- Ll _ ,----"'\ _Ll-_TRANSMISSIONLINE:STOC.K ",S·12430K-86Z717CROSSOVE:RA ' ~I"!.~ULI\TOR~ '--1--' ,~OCK NO 43Z7,,'I- (~~RANSMISSION ~LINE:STOCK N9'Z430ISINGLE-DOUBLET ANTENNA DOUBLE-DOUBLET ANTENNAL= 1.30 feet for 16o-Meter (1,900 kc) Band Ll == 1.30 feet for 1.6o-Meter BandL= 65 " "80-"(3,800 kc)"Ll. == 65 " "80-" "L= 33 " "40- " (7,'50 kc)"Ll. == 33 " 40-" "L= ,6" "~o-"(14'~OO kc)"Ll. = ,6 "~o-" "L= 8 " ",0-"(::;;:8,000 kc)"~= 65 " 80-" "~= 33 " 40- " "~= ,6" ,,0-" "~= 8",0-" "Doublet Antenna ConnectionsSPEAKER OR PHONES-This receiver is designedfor use with a permanent-magnet dynamic typespeaker, having a voice-coil impedance of from 2 to 3ohms. The RCA Stock No. MI-8303 speaker (seeFigure 2) is designed and recommended for the purpose.The terminals for connection to the speaker areshown in Figure 3A.The RCA Manufacturing Company also producestwo deluxe extended range speakers. One, MI-8314,is housed in a walnut cabinet; the other, MI-8314A,is contained in a walnut cabinet for wall mounting.A jack is provided on the right-hand side of thecabinet, near the front, for plugging in a pair of 600-ohm headphones. The speaker is automatically disconnectedwhen the phones are plugged in.RACK PANEL MOUNTING OF RECEIVER­If it is desired to mount the receiver on a rack panel,the necessary panel and supports (MI-8304) are availablefor this type of mounting. This set of parts includeseverything necessary to mount the standard re~ceiver chassis to the rack panel.The receiver chassis is first removed from the cab~inet. For this purpose first remove all knobs from thecontrol shafts. Next remove the perforated metalscreen on the back of the cabinet by taking out thefive self~tapping screws. Remove the five Ij4~inch ma~chine screws underneath the cabinet. Next discon~nect the tuning meter on the front panel. The chassisis now ready to be removed from the cabinet. Thechassis should be tipped up at the rear just before en~tirely removing to prevent hitting the two frontbrackets against the upper angle at the rear of thecabinet.With the chassis removed, the dial window maskand window should then be assembled to the rack7panel. The panel is fastened to the chassis by meansof six machine screws. Spacers are placed betweenthe panel and the chassis. The side brackets shouldthen be attached.One of the headphone jacks should be wired directlyto the receiver output terminals. This jack willthen allow the receiver output to be monitored in in~stallations where the output of the receiver is con~nected to a line.The other headphone jack should be connected exactlylike the one on the side of the receiver chassis.This may be simplified in the following manner: Itwill be observed that the ground and output terminalconnections are already connected to the first jack.Jumpers may then be placed between the two jacksfor these connections. The remaining connection isto the output transformer primary. This lead shouldbe removed from the jack on the side of the receiverand connected to the jack on the panel. The purposeof this second jack is to connect a pair of headphonesand at the same time remove the receiver output fromthe line. Thus, in a diversity system, one receivermay be easily removed from the combined output andtuned or adjusted without disturbing the others.A receiver, mounted on a 10-15/32 inch x 19 inchpanel, ready to be installed on a rack, is also available.The Model AR-77, MI-8302G, is for use with a powersupply of 105-125 volts, 50/60 cycles; and the ModelAR-77E, MI-8302H, is for use with 105-130; 140-160;195-250 volts, 50/60 cycles.RACK PANEL MOUNTING OF LOUD­SPEAKER-The loudspeaker, Stock No. MI-8303,may be converted for rack mounting by purchasingthe panel kit, MI-8305, available for this purpose.

· -------.,..OPERATIONBefore attempting to operate the receiver, this en'tire section should be carefully studied so that theoperator may obtain a general understanding of thevarious controls and their functions and adjustment.The symbols on the panel used to designate the variouscontrols should be learned with respect to func'tion as shown on Figure 1.TUNING-In tuning this re~eiver, the various con ..troIs should be approximately set for the class of signalit is desired to receive. Select the frequency banddesired by rotating control knob "R" until the properscale appears in the slot at the upper left of the panel.Before proceeding, adjust the antenna trimmer tomaximum for this band (see next paragraph-HAn ..tenna Trimmer"). The frequency calibrations on themain dial scales are correct for tuning. when the band ..spread dial is turned to its maximum frequency posi'tion only.The bandspread dial is calibrated for the amateurbands of 10, 20, 40' and 80 meters only. To use thebandspread on these bands, set the main tuning dialaUhe highest frequency on that band, then tune withthe bandspread dial. On the 160-meter band, the calibrationson the main dial are spread sufficiently so thatit is not necessary to use the bandspread tuning. Foran extremely accurate calibration, set the bandspread .dial for a signal of known frequency, and then adjustthe main dial until the station is tuned in. When thisposition has been obtained, note the setting of the ar'bitrary scale with its vernier index, on the main dial.For commercial operation, or bands other thanAmateur, the arbitrary scales should be used on themain tuning and bandspread dial. If the bandspreadis not used, it should be left at the high frequencyend of its range and then the main dial calibration iscorrect.Curves may be plotted, giving arbitrary 'scale read,ings versus frequencies, on any band, by observingthe readings on the arbitrary scales for a number ofstations of known frequency on the same band, andworking them on a suitable graph or chart.ANTENNA TRIMMER-Before tuning on anyfrequency range, the antenna trimmer should be ad,justed for maximum performance on that band. Thiscontrol may be adjusted by tuning for maximum back,ground noise. Occasionally it is desired to test a sig'nal that seems out of place, to see whether or not it isa fundamental signal or an ·"image."When adjusting the antenna trimmer, if the maxi,mum signal point coincides with the point of maxi-­mum background noise, the signal is a fundamental.If the control. does not affect the signal strength, orif it is maximum at some other point, the signal heardis an "image."CRYSTAL SELECTIVITY SWITCH-For generaloperation while tuning. it is recommended thatthe crystal switch be in the "OFF" position. Afterthe main tuning dial has been set at the desired point,the crystal may be placed in the circuit while tuningover the bandspread range. Crystal selectivity posi'tions 1 and 2 should be used for phone or modulatedsignal reception and 3, 4 and 5 for CW telegraph reception.It will be noticed that when tuning in a modu,lated signal with the crystal in, the speaker volume isgreater on either side of the point which gives themaximum tuning meter indication. The reason forthis is that the carrier voltage controls the gain of thereceiver by means of the A.V.C. circuit, and if thecarrier frequency is detuned slightly from resonance',the gain of the receiver increases so that part of theside band frequencies are amplified very much morethan they are when the carrier is tuned to exact res'onance. This is characteristic and normal for receiverswith this degree of selectivity and provided withA.V.C. Care should be taken to tune the receiverfor a maximum meter indication. Very much betterresults will be obtained. The background noise andadjacent channel interference will be materially re'duced.This receiver has been designed to have a selec'tivity characteristic which is slightly flat at resonancewhen the crystal is out, so that better fidelity of receptionmay be enjoyed when interference conditionspermit. It is therefore likely that when the crystal isplaced in the circuit, slight retuning may be neces'sary. This is due to the fact that exact tuning is muchmore necessary when using a sharp I, F circuit thanwhen using a broad circuit.CRYSTAL PHASING CONTROL-There is anormal or "'neutral" position for this control, in whichposition it should be set for all normal reception. Tolocate this position, set the Crystal Selectivity Switchon position 3 or 4, and, using high gain with no in'coming signal, adjust the phasing control for mini,mum noise. This control should be changed from thisposition only when a strong signal is producing aheterodyne action with the desired signal. In thiscase, the control should be adjusted for a minimumheterodyne effect.VOLUME AND SENSITIVITY CONTROLS­For phone reception the sensitivity control should beset at maximum and the audio volume control used toobtain the desired volume. For CW telegraph recep~tion the audio volume control should be set at three'fourths to maximum position and the desired volumeobtained by adjustment of the sensitivity control.NFB-AVC-BFO SWITCH-These letters stand for"NEGATIVE FEED-BACK," "AUTOMATICVOLUME CONTROL," "BEAT FREQUENCYOSCILLATOR." The "NFB" position places thecompensated negative feedback in the audio circuits,resulting in an increase in fidelity. This is useful fortests in voice transmissions and for entertainmerit usesuch as on broadcast reception. When using this po'sition the volume control must be advanced slightly.This position is not recommended for other forms ofreception.8

The AV.C. is in operation on both the "NFB" and"A VC" positions of this switch.The AV.C. is "OFF" when the switch is in the"BFO" position. This position connects the beat'frequency oscillator.BFO FREQUENCY CONTROL-This control isprovided to secure any desired audio beat frequency,for the reception of CW code signals. It should beset slightly off the cent~al position, in normal use.The exact position may be found by experiment.With the crystal switch "OFF," the desired beat notemay be obtained by tuning the receiver. However,in conditions of interference, when the crystal filteris used, the receiver must first be tuned to the desiredsignal, regardless of the beat frequency produced. Ifthe beat note is not satisfactory, it may be changedwith the BFO control. In other words, -first tune formaximum signal strength, then adjust for the desiredaudio pitch.When tuning in the same direction (that is, goingfrom the high frequency to the low frequency end ofthe band, or vice versa), ALL signals will be changingin pitch in the same direction when resonance isreached. That is, the pitch will either be increasingor decreasing, depending on whether the BFa controlis on one side or the other side of I .. F resonance. Itdoes not matter on which side the BFa control isplaced, the CHANGE OF PITCH should be notedwhen tuning. If the change of pitch is opposite tothat known to exist when passing through resonance,the signal is an audio image. Never try to receive anaudio image. The signal can be made much strongerby tuning to the other side of zero beat.NOISE LIMITER LEVEL CONTROL-Whenstarting to tune the receiver, this control should beset in the "OUT" position, or advanced about onequarterto three-quarters of the way in the counterclockwisedirection. Should external noise conditionsinterfere with reception, this control may be advancedas necessary, avoiding distortion of the signal. Thiscontrol may be found especially helpful for reducingcertain types of interference encountered on the 10,meter band. For CW reception with the noise,lim'iter, the sensitivity control should be advanced, andthe volume control reduced until limiting action oc'curs.TRANSMIT-RECEIVE SWITCH-This switchopens the plate circuits of the receiver on the transmitposition and shorts the two terminals on the antennaterminal strip (shown in photograph Figure 3A),which may be connected to a relay for operation ofthe transmitter.In addition, terminals J2 and J3 are provided sothat, if desired, the plate circuit of the receiver maybe opened by a transmitter switch. Note that theseterminals are at plate potential.TUNING OR "s" METER ADJUSTMENT­The "s" meter should normally give a low scale readingwhen no signal is being received. To adjust thismeter, tune the receiver to a point free of signals, turnthe sensitivity control to maximum, switch in A.V.C.switch crystal "OUT," have antenna trimmer turnedoff resonance, and then adjust the potentiometer atthe back of the receiver as shown in Figure 4 untilthe meter pointer just coincides with -the mark at thelow end of the scale. The meter will usually riseslightly when the antenna trimmer is tuned to res'onance.The calibration of this meter is arbitrary, since nostandard has been set for conversion of the "S" unitsto microvolts. However, in this receiver, "81" isequivalent to approximately 0.5 microvolt input to thereceiver. Each unit above this is 6 db up to "SQ".Thus, "82" is equivalent to 1 microvolt, "83" to 2microvolts. Above "89" the meter is calibrated to40 db, which would be equivalent to' 12,800 microvolts.For CW telegraph reception, the "s" meter providesa visual indication of the position of the sensi,tivity control.BREAK-IN OPERATION-Break-in operationmay be obtained on CW telegraph operation by connectinga separate antenna to th,e receiver. A singlewire antenna or a doublet tuned to a different bandthan that on which the transmitter is' working is rec'ommended. If a doublet antenna tuned to the trans'mitter frequency is used, sufficient voltage' may beinduced in the receiving antenna to damage the re'ceiver.DIVERSITY RECEPTION-Two or three ofthese receivers may be connected together for diver'sity reception of modulated signals, with no additionalequipment necessary. Each receiver must be providedwith a separate antenna in the usual manner. Theunconnected terminal on the back of the receiver,shown in Figure 3, is connected inside the receiver tothe A.V.C. circuits. This terminal must be connectedto the corresponding terminals of the No.2 and No; 3receivers. The receiver outputs should all be con'nected in parallel. Note that one of the output term'inals of this receiver is at ground potential.FOR CONNECTION TO A TELEPHONELINE-It is recommended that a transformer suchas RCA type MI-4904 be used. The connections tothe type MI-4904 transformer should be made asfollows:1. Connect the output terminals of one or moreModel AR-77 receivers in parallel to terminals No.4 and No. 41 of the transformer.2. Connect the SOO~ohm line to transformer term'inals lA and 3B.3. Connect a jumper between transformer term'inals 1B and 3A4. Connect a 500 to 600 ohm, 1/2 to 1-watt resistoracross the SOO-ohm line, or across terminals 1Aand 3B.Connecting a pair of headphones in the jack oneach receiver will disconnect it from the combinedoutput so that the tuning or other adjustments maybe checked. Obviously, the. audio volume control oneach receiver should be set to approximately the samelevel. For CW telegraph diversity reception, it isrecommended that a combining and tone,keyer unitbe used.9

,CIRCUIT DETAILS AND FEATURES-In readingthe following discussion of the electrical circuit,reference should be made to the schematic diagram,Figure 5.INPUT COUPLING-The antenna coupling systemis designed to provide optimum coupling fromtransmission lines of jO to 500 ohms, or from cowventional antenna and ground systems. The couplingcoils are balanced to ground and may be connecteddirectly to a balanced transmission line. An antenna. trimmer capacitor adjustment is provided on the frontpanel to it?sure first circuit resonance with any awtenna system.RADIO-FREQUENCY AMPLIFIER-The r-famplifier is designed to provide as much selectivity aspossible ahead of the first detector. The amplificationis adjusted to provide optimum signal to noise ratioby making noise contributions of circuits following thefirst tube negligible in comparison with the noise contribute9by the first r-f grid circuit. A uniform amplificationis ,obtained over aU frequency ranges. Onthe tw'o highest frequency~ ranges the oscillator frequencyis .placed below the signal frequency. Thisgives better freedom from image signals in the higherfrequency amateur bands.BAND SPREAD-Band spreading is accomplishedby means of a capacitor gang having sections of capacitysuitable for each amateur band. The sectionsof this capacitor are connected by the band switch sothat on each amateur band, proper size of capacitor isused _to spread the band over the entire tuning dial.The dials. are directly calibrated in frequency.R-F HETERODYNE OSCILLATOR-The doscillatorcircuit is of the tuned-grid type with plate circuitfeedback. A voltage regulator is used to stabilizethe plate voltage. Temperature changes are compensatedfor by a special capacitor. This capacitor iscomposed of a small bi-metal plate, which is adjustedto have a- temperature coefficient which will compensatefor all other circuit changes. This type oftemperature compensation was fOll-nd to be quite satisfactorysince the circuit minimum and maximum capacitiesare the same on the higher frequency ranges.That is, the temperature coefficient of this compensatingcapacitor is adjusted "at the factory for bestresults on the high frequency end of the highest frequencyrange. The compensation is then near optimumon the high frequency end of each band. As thereceiver is tuned from the high frequency end to thelow frequency end of each band more tuning capacityis added and less compensation is needed. Since thecapacity of the compensating capacitor is small comparedto the tuning capacitor, less compensation results.Thus, a fairly uniform temperature character-, istic is obtained over a very wide frequency range.INTERMEDIATE-FREQUENCY AMPLIFIER-·As may be seen from the schematic diagram, twostages of i-f amplification are used. A crystal filter isplaced between the first detector and the first inter-MAINTENANCEmediate amplifier. This -filter is adjustable by meansof a control on the front panel and provides -five positionsof selectivity. A crystal phasing control of the. usual type is also provided on the front panel. Theintermediate frequency is 455 kc.BEAT-FREQUENCY OSCILLATOR-The BFOsecond heterodyne oscillator used for. CW receptionis a separate pentode. The coupling to the seconddetector is just sufficient to provide suitable heterodyneaction. A panel control is provided for changingt~e frequency a small amount so that any desiredaudio beat-frequency may be obtained. ,AUTOMATIC VOLUME CONTROL AND "S"METER-The A.V.C. circuit is a simple diode rectifier.Referring to the schematic diagram, Figure 5,the received signal carrier produces a voltage acrossR-38 which is filtered by R;36 and C-72 and appliedto the control grids of the r-f and i-f amplifiers. The"S" meter is connected in the cathode circuit of thefirst i-f tube and thus records changes in plate currentcaused by changes of A.V.C. voltage applied to thegrid. This type of "S" meter circuit provides the desiredwide range and the greater portion of the scaleis approximately linear with respect to dh input.NOISE LIMITER-A noise limiter is provided inthe second detector circuit. The limiter is manuallyadjusted. This provides best limiter action since noisevoltages cannot increase the limiter bias.It has been found that noise s~ch as that producedby the ignition systems of automobiles may have aneffective value in excess of that of a weak signal.This is particularly true on the lO-meter band. Inorder to be effective, the limiter must have a bias or"gate opening" of not more than twice the signal carrieramplitude. If this "gate opening" is provided bythe signal such as is done in present automatic noisecircuits, the noise voltage, if it has a higher effectivevalue than the signal; will open the "gate" to such ahigh value that the limiter circuit is ineffective. Theaction of the noise circuit in this receiver is such asto make signals readable which are below the effectivenoise voltage.Referring to the schematic diagram, Figure 5, 'thesignal and noise voltages appear across R-32 and thenoise peaks alone appear across R-33, since the biasapplied to R-31 by the potentiometer R-34 preventsthis diode from operating with the signal voltage.The sum of these voltages (across R-32 and R-3l)are applied to the audio amplifier. It is apparent thatthe noise peak voltage across R-3 2 is out of phase oropposed to that across R-33. The "balance" of thiscircuit is adjusted by potentiometer R-33. The potentiometerR~ 34 is the front panel bias control.SERVICE-This receiver has been carefully adjustedand aligned by the manufacturer befor,e ship~ment, and should maintain its adjustments over a considerableperiod of time. It is recommended that anymajor adjustments or repairs be made by a compe~~tent service man.II ,10

TUBES~In a receiver which is used quite consist,ently, the first trouble which is likely to occur is thatof deficient vacuum tubes. Usually the symptom ofdeficient tubes is a noticeable decrease in ~he sensi,tivity of the receiver. If the receiver will operate onall bands, but with low sensitivity, the tubes shouldbe removed and checked. The tube locatlOns areshown on the label on the large metal shield on topof the chassis.BAND CHANGE SWITCH-After a long periodwithout being operated, the band change switch maybecome noisy or inoperative because of dust or oxidefilm On contacting surfaces. In some cases, normaloperation may be restored by rotating the switch anumber of times. If it is found impossible to ,cleanthe switch sufficiently by rotation, the defective switchsection must be located and replaced. The receivershould be removed from the cabinet and operated ina position such that the switch sections are a,ccessible.With the switch in the defective position, a slightmovement of each section with an insulated screw'driver will usually -determine the defective section.To remove a switch section it will first be necessaryto remove the switch shaft. The antenna trimmercontrol shaft must also be removed in order to un'solder the leads on the tuning capacitor. After allleads are disconnected the entire coil and switch assemblymay be removed by taking out the threescrews holding the assembly to the chassis.TEST OF CIRCUIT ALIGNMENT-Under nor·mal operating conditions the r,f amplifier and o~ci~'lator circuits should remain in line. If, however, It 1Sfound desirable to check -the alignment of these circuits,the following test should first be made. Dis·connect the antenna or transmission line and connecta 50, to 300'ohm carbon resistor across the two an'tenna terminal posts. Connect an output voltmeter tothe output_ of the receiver and connect a 20-ohm re'sistoI: across the meter. Turn the sensitivity and volumecontrols to maximum. The A.V.C. switch shouldbe on the A.V.C. position. The output noise volt,age should be at least 0.1 volt, with the antenna trim'mer tuned to resonance. The maximum noise voltageis a direct measurement of the sensitivity of the re'ceiver. 1f the test shows that this voltage is less than0.1 volt, the circuits should be realigned. First besure that the decreased sensitivity is not caused bypoor tubes. It probably will not be necessary to alignall bands; however, the correct procedure for all bandsis given below.ALIGNMENT OF I·F CIRCUITS-Remove thebottom cover plate of the receiver cabinet, tune in asteady outside signal on one of the lower frequencybands with the AV.C. switch on the BFO positionand the crystal filter switch in position 2 or 3. ThesiO'nal should be tuned for a peak response at thecr~stal frequency. Do not. use too strong a signal.The sensitivity control should be adjusted for ap·proximately 1 volt output. Referring to Figure 5 ad·JUSt T·l, L·19, T·2, T·3 and T·4 for a maximum out·put voltage. The signal should now be detunedapproximately 1,000 cycles and adjustments T·l, L·19and T,2 retuned for a maximum output.The T·2 adjustment on top of the chassis is sealedwith polystyrene cement. Applying a soldering ironto the adjusting screw for a few seconds will softenthe cement. The ihtermediate frequency is 455 kc.ALIGNMENT OF R·F AND OSCILLATORCIRCUITS-Under usual conditions, the oscillatorfrequency will not shift far enough to throw the fre·quency calibration off, therefore, unless it is foundthat the frequency calibration is incorrect, the oscil,lator adjustments should not be changed. In anycase, the oscillator circuit should not be changed un'less a frequency calibrated test oscillator is available.The following procedure is for the r·f alignment ofband No.1 (540 to 1,300 kc). Tune in a signal"nearthe high·frequency end of the band. (Do not usetoo strong a signal.) Reduce the sensitivity controluntil the output is approximately 1 volt. Referringto Figure 6, adjust C,18 and the antenna trimmer controlon the front panel for- maximum output. Next,tune in a signal near the IQW frequency end of theband. Adjust L·l and L·7 for a maximum signal out·put. The same procedure may be followed for allhands. Make sure that the bandspread tuning is atthe high·frequency end of the scale. The bottomcover should be held over the oscillator trimmer capacitorswhile adjusting the high frequency end ofeach band, so that when the cover is replaced, thefrequency will not shift. The adjustments for eachparticular band are shown in the table herewith.R· F Det. Det. Osc. Osc.Band Ind. Ind. Cap. Ind. Cap.540· 1,340 L·l L·7 C·18 L·n C·241,340· 3,300 L·2 L·8 C·17 L·14 c·n3,300· 5,800 L·3 L'9 C·22 L·15 C·285,800·10,200 L·4 L·lO cm L·16 C·2710,200·18,000 L·5 L·l1 C·20 L·17 C·2618,000·31,000 L·6 L·12 C·19 L·18 C·25DIAL SHUTTER ADJUSTMENT-If the dialshutters do not line up with the dial calibration, theymay be adjusted by means of an idler pulley bracketwhich adjusts the tension of the cord. By looseningthe two screws which clamp the idler pulley bracketto the chassis the bracket may be shifted until tbeshutter opening lines up with the dial scale.Another adjustment may be made by loosening thetwo nuts on adjusting screw fastened to back of shut,ter. To raise or lower the shutter, adjust the nutsaccordingly.NOISE BALANCE ADJUSTMENT-This ad·justment is the potentiometer mounted on the rightflange of the chassis (R·33). The correct adjustmenthas been carefully made at the factory and should or·dinarily require no further attention. However, inservicing the receiver, in the event that the adjustmentis accidentally moved. it may he reset as follows:First tune in a strong modulated signal such as abroadcast station. Next turn the noise control on thefront panel all the way clockwise. Now adjust thepotentiometer for a minimum signal output. Thispoint will be found to be very sharp. When properly11

· -------,.....adjusted, the signal output will be quite low until thenoise control on the front panel is turned back counterclockwise.TUBE SOCKET VOLTAGES-If the receiver isfound to be completely inoperative, it is likely that aresistor is open-circuited or a capacitor is short,cir',cuited. The bottom cover plate of the receiver cab-inet should be removed. The tube socket terminalvoltages should be measured and should be approximatelythe values given in the table below. Thetubes should remain in the sockets for this test. Avoltmeter having a resistance of at least 50,000 ohmsshould be used. Place switch on BPO and turn SensitivityControl to maximum.TUBE SOCKET VOLTAGESSuppressor Oscillator Heater (AC)Cathode to Screen Grid Plate toTube Symbol Grid to Plate to Pin No.2 toGround to Ground GroundGround Ground Pin No.7RCA6SK7(R-P Ampli- 3.0 90 180 3.0fier) V8 (Pin No.5) (Pin No.6) (Pin No.8) (Pin No.3) - 6.1RCA6K8 2.6 75 240 60(Det. Osc.) V6 (Pin No.8) (Pin No. 4) (Pin No.3) - (Pin No.6) 6.1RCA-6K7 Mia(1st I-P 3.0 82 200 0Amp.) V5 (Pin No.5) (Pin No.6) (Pin No.8) (Pin No.3) - 6.1RCA6S]7(Beat Preq. 0 50 15Osc.) V2 (Pin No.5) (Pin No.6) (Pin No.8) - - 6.1RCA-6SK7(2nd I-P 4.5 115 220 ". 4.5Amp.) V7 (Pin No.5) (Pin No.6) (Pin No.8) (Pin No.3) - 6.1RCA-6H6(2nd Det.) VI - - - - - 6.1RCA6SQ7(A-P Amp.- 0.7 85 6.1A.V.C.) V3 (Pin No.3) - (Pin No.6) - - (Pin No.7 toPin No.8)RCA-6P6G 16 260 250(Output) V4 (Pin No.8) (Pin No.4) (Pin No.3) - - 6.15.1375 a.c. (Pin No.2 toRCA5Y3Z 300.0 (Pins Nos. Pin No.8)(Rectifier) VIO (Pin No.8) - 4 & 6) - - (Caution-300 v. d.c.,voltage toground)RCA-YR-150(Voltage 150Regulator) V9 - - (Pin No.5) - - -PARTS LISTRECEIVER PARTSStockItemDESCRIPTIONItemDESCRIPTIONStockNo.No.IC-l. C-2, C-3, Condenser - 3-gang, 6-section C-29 Condenser-3 to 25 mmfd' J7-C-4, C-5, main tuning-less split gear, plate beat-frequency oscillatorC-6 brass pinion, gear, and bear- control 34893ing assembly 34879 C-30 Condenser-2.5 to 17.9 mmfd.,C-7, C-8, C-9, Capacitor - 3-gang, 9-sectitm 5-plate crystal phase adjust-C-I0, C-l1, band-spread-Iess split gear, ing condenser 37238C-12, C-13, brass pinion gear, and bear- C-31 Capacitor-180 mmfd., 400 volts 13003C-14, C-15 ina assembly34880 C-32, C-33, Capacitor-O.OI mfd., 1000 volts 43764C-16 Con enser-3.6 t~' ·35 . mmfd.;C-3410-plate antenna adjuster 34892 C-35 Capacitor-68 mmfd., 400 volts 13057C-17, C-18 Condenser-Air trimmer 12714 C-36, C-37 Capacitor-Same as C-32C-19, C-20, C-38 Capacitor-IO mmfd .• 400 volts 13200C21, C-22 Condenser-Air trimmer 12807 C-39 Capacitor-O.I mfd., 400 volts. 37327C-23, C-24, Condenser-Same as C-17 C-40 Capacitor - 1000 mmfd., 400C-25, C-26 volts 12635C-27, C-28 Condenser-Sa,me as C-21 C-41 Capacitor-5.6 mmfd., 400 volts 1281412

PARTS LIST (Continued)ItemDESCRIPTIONStockNo.ItemDESCRIPTIONStockNo.C-42C-43C-44C-45C-46C-47C-48C-49. CoSO,C-51C-52C-53, C-54,C-55C-56, C-57C-58. C-59,C-60C-61C-62C-63C-64C-65, C-66C-67C-68C-69C-70C-71C-72, C-73C-74C-75C-76C-77, C-78C-79C-80C-81C-82, C-83C-84, C-85C-88C-89, C-90C-91C-92J-lJ-2, J-3L-lL-2L-3L-4L-5L-6L-7L-8L-9L-l0L-llL-12L-13L-14L-15L-16L-17L-18L-19L-20Capacitor-330 mmfd., 400 voltsCapacitor-2700 mmfd., 400voltsCapacitor-Same as C-40Capacitor-D.OS mfd., 400 voltsCondenser - Stabilizing condenserCapacitor - 120 mmfd., 400voltsCapacitor-Same as' C-45Capacitor - 100 mmfd., 400voltsCapacitor-Same as C-32Capacitor-Same as C-45Capacitor - 220 mmfd., 400voltsCapacitor-Same as C-45Capacitor-Same as C-49Capacitor-56 mmfd., 400 voltsCapacitor-12 mmfd., 400 voltsCapacitor-47 mmfd., 400 voltsCapacitor-Same as C-56Capacitor -1200 mmfd. 400voltsCapacitor-Same as C-45Capacitor-Same as C-49Capacitor-Same as C-64Capacitor-Same as C-45Capacitor-Same as C-63Capacitor-6.S mmfd.Capacitor-Same as C-4SCapacitor-5-5-5 mfd., 350 voltsCapacitor-Same as C-39Capacitor-Same 'as C-49 (containedin T-5)Capacitor-Same as C-64 (containedin T -5)Capacitor-Same as C-45Capacitor - 20-20 mfd., 450voltsCapacitor-Same as C-32Capacitor-Same as C-45Capacitor-4 to 100 mmfd.,mica trimmerCapacitor-0.25 mfd.Jack-fleadphone jackJack-Phone tip jack for transmitterrelay connectionsCoil-Antenna 540-1340 kcCoil-Antenna 1340-3300 kc.Coil-Antenna 3.3-5.8 mcCoil-Antenna 5.8-10.2 mcCoil-Antenna 10.2-18.0 mcCoil-Antenna 18.0-31.0 mcCoil-Detector 540-1340 kcCoil-Detector 1340-3300 kc.Coil-Detector 3.3-5.8 mcCoil-Detector 5.8-10.2 mcCoil-Detector 10.2-18.0 meCoil-Detector 13.0-31.0 meCoil-Oscillator 540-1340 kcCoil-Oscillator 1340-3300 kc.Coil-Oscillator 3.3-5.8 mcCoil-Oscillator 5.8-10.2 meCoil-Oscillator 10.2-18.0 me.Coil-Oscillator 18.0-31.0 me ..Crystal Filter Assembly-Coilcore, capacitor and form-lessshield can-includes C-SlReactor-Filter reactor12952300573732834895127241272012694127231300213141130541407934890348893721948397903338913723237233372343723537236372373722637227372283722937230372~13722037221372223722337224372253489135327M-lR-lR-2R-3R-4R-5R-6R-7R-8R-9R-l0R-llR-12R-13R-14R-15R-16R-17R-18R-19R-20R-21R-22R-23R-24R-25R-26R-27R-28R-29R-30, R-31R-32R-33R-34R-35R-36R-37R-38R-39R-40R-41R-42R-43R-44, R-45,R-46R-47R-48R-49R-51R-52, R-54S-1S-2S-3S-4S-5S-6S-7S-8S-9S-10Meter-Carrier level metercompleteResistor-470,OOO ohms, 711 wattResistor-lO,OOO ohms, 711 wattResistor-330 ohms, 711 wattResistor-22,OOO ohms, ~ wattResistor-150,OOO ohms, ~ wattResistor-Same as R-4Resistor-Same as R-3Resistor-Same as R-5Resistor-Same as R-2Resistor-Same as R-4Resistor-IO ohms, ~ wattResistor-Same as R-2Resistor-6800 ohms, ~ watt.Resistor-IS,OOO ohms, ~ wattResistor-Same as R-4Resistor-68,000 ohms, % wattResistor-Same as R-lResistor-68 ohms, ~ watt.Resistor-220 ohms, ~ wattControl-80-ohm tuning meterzero adjustmentControl-30,OOO-ohm sensitivitycontrolResistor-Same as R-1Resistor-Same as R-4Resistor-Same as R-16Resistor-Same as R-2Resistor-Same as R-3Resistor-47,000 ohms, % wattResistor-4700 ohms, % wattResistor-IOO,OOO ohms, Yz wattResistor-Same as R-5Resistor-Same as R-27Control-l00,OOO-ohm noise balanceadjustmentControl - 30,000-ohm limitercontrolControl-SOO,OOO-ohmvolumecontrol and power switch(S-I)Resistor-220.000 ohms, Yz wattResistor-5600 ohms, Yz watt.Resistor-1 megohm, % watt.Resistor-lOOO ohms, % watt.Resistor-Same as R-29Resistor-Same as R-29Resistor-Same as R-IResistor-820 ohms, % watt.Resistor-Same as R-29Resistor-Same as R-lResistor-470 ohms, 1 wattResistor-Same as R-29Resistor-3000 ohms, 10 watts.Resistor-Same as R-29Power Switch-Combined withR-35Switch-RangeSwitch-RangeSwitch-RangeSame as S-2switchswitchswitchwafer.wafer.wafer-Switch-Range switch wafer.Switch-Range switch wafer­Same as S-2Switch-Range switch wafer­Same as S-5Switch -- Crystal selectivityswitchSwitch-A.V.C. switchSwitch -- Transmit-r e c e i v eswitch349463552437137180393713637271184713727312759372743727537276349103494037139304941973634941349383493935510372773552119739355133727834943349153491634914349123491134913I, !,I; IiJ13

,PARTS LIST (Continued)ItemDESCRIPTIONStockNo.ItemDESCRIPTIONStockNo.T-IT-2T-3T-4T-5T-6T-7T-7T-7X-ITransformer - First detectorplate I-F transformer complete-includesC-47, R-12. 34885Transformer-I-F transformercomplete - includes C-56,C-57, R-25 34887Transformer-I-F link trans- !former complete - includesC-61, C-63, R-28 34884Transformer-Diode I-F transformercomplete - includesC-62, C-64 . 34888Transformer - CW oscIllatortransformer complete - includesC-80, C-81, R-42 34886Transformer - Output transformer. . 14355Transformer-l05-115 volts, 25-cycle power transformer(Used in MI-8302F only)" 34693Transformer - 110 -125 -150-210-240 volts, 50/60 cyclepower transformer (Used inMI-8302E only) 37243Transformer-l05-125 vol t s,50/60 cycle power transformer(Used in MI-8302Dand MI-8302G only) 9551Crystal-455 kc crystal filterand caseMI-7593MISCELLANEOUSBracket - Flywheel mountingbracket 34903Board-3-contact t e r min a 1board 12716Board-5-contact t e r min a 1board 34896Cord-Dial drive or rangeshutter control cord 32634Coupling-Range switch couplingwith set screws 34937Detent-Range switch detentplate assembly 34936Dial-Transluscent band spreaddial complete with hub andset screws 34900Dial-Transluscent main tuningdial complete with hub andset screws 34901Drum-Large dial drive drumcomplete ......... 34908Flywheel - Tuning flywheelwith set screws 34902Gear-Brass pinion gear andbearing assembly 34882Gear - Spli-t main or bandspread condenser drive gear.Guide, Band indicator shutterguide rods and strap assemblyLamp - 6.3 volt dial lamp,Mazda No. 44Pulley-Left-hand band indicatoridler pulley and bracketPulley-Right-hand band Indicatoridler pulley and bracketPulley-Small dial drive pulleyand hub with set screws.Scale - Calibrated stationaryvernier scale-less supportScrew-No. 8-32 set screw fordial drive drumShaft-Dial drive flywheel shaftShaft-Range switch shaft-1 DY4 inches longShutter-Left-hand band indicatingshutter and pilot lampbracket assemblyShutter-Right-hand band indicatingshutter and pilot lampbracket assemblySocket-8-contact p hen 0 I i csocketSocket-8-contact wafer socketSpring-Band indicator shutterlift springSpring-Dial drive cord tensionspringSpring-Triple loop spring usedon rear end of band switchshaftSupport-Vernier scale supportand hub assemblyKnob-Antenna adjuster controlknobKnob-Bar type control knob(8 used)Knob-Main tuning or bandspread control knobKnob-Range switch controlknobMask-Metal window maskplateNut-Clamping nut for airtrimmersSocket-Pilot lamp socketSocket-Pilot lamp socket andclipWindow-Clear dial windowsheet348813489911891372413724231271349051435034904349353723937240180073308434898324813494434906349493495034947"349483495314028349513490934952SPEAKER PARTSItemDESCRIPTIONStockNo.ItemDESCRIPTIONStockNo.Cone-Speaker cone and voicecoilEscutcheon-uRCA" escutcheonPlug-3-contact male plug forspeaker31310130595118Socket-3-contact female socketfor speaker cableSpeaker-Speaker unit only lesspanel5119971214

A. Rack.Type ChassisB. Cabinet. Type ChassisFigure 3~General Purpose Communication Receiver15 (Chassis Top Views)

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