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Zenith Radio Corporation Y504B Service Manual

High fidelity and stereo fm models
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Table of Contents

ERVICE MANUAL
IG
FIDELITY
AND STEREO FM MODELS
ZENIT RADIO CORPORATION
1900 N. AUSTIN AVENUE
C ICAGO, ILLINOIS 60639
PRICE $2.50
•
F 18
PART NO. 923-^58

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  • Page 1 ERVICE MANUAL FIDELITY AND STEREO FM MODELS ZENIT RADIO CORPORATION 1900 N. AUSTIN AVENUE C ICAGO, ILLINOIS 60639 PRICE $2.50 • F 18 PART NO. 923-^58...
  • Page 3 INDEX C ASSIS SC EMATIC LAYOUT PARTS LIST C ASSIS PAGE PAGE PAGE — 1Y20Z 2ZT21 100, 101 2ZT22 100, 101 2YT23 58, 59 2ZT24 2AT30 6ZT20 59, 60 6AT24 60,61 8ZT20 110, 111 9AT27 61,62 10YT26 62, 63 10ZT30 116, 117, 118 63, 64, 65 10ZT31...
  • Page 4 POWER STYLE COLOR MODEL MODEL INC ES NUMBER (IN O MS) OUTPUT -4" 49- 096 Blue & Y20Z Tube Y504B Table Phono Only (w/handle) White (lift lid) - - - -4" 49- 096 Tube Red & Y20Z Y504D Table Phono Only...
  • Page 5 FEATURES OF IG FIDELITY & STEREO FM MODELS RECORD C ANGER OT ER FEATURES REMOTE NUMBER RECORD MOUNTING CARTRIDGE STYLUS NOTE 1 TYPE INDICATOR SPEAKER STORAGE LIG T PROVISION Manual Shelf 42- 6 Player 56-480 Manual Shelf 42- 6 Player 56-480 Manual Shelf...
  • Page 6 FEATURES OF IG FIDELITY & STEREO FM MODELS SPEAKER CABINET C ASSIS VOICECOIL SIZE PART STYLE COLOR MODEL TYPE POWER IMPEDANCE MODEL NUMBER INC ES OUTPUT (IN O MS) 2-4" 49- 47 Brown 8ZT20 8 Transistor Table Z538P Phono Only (w/handle) &...
  • Page 7 FEATURES OF IG FIDELITY & STEREO FM MODELS RECORD C ANGER OT ER FEATURES REMOTE RECORD INDICATOR NUMBER MOUNTING CARTRIDGE TAPE SPEAKER STYLUS NOTE 1 STORAGE LIG T PROVISION 69-358 Shelf 42- 48 56-528 69-359 Shelf 42- 48 56-528 69-360 Shelf 42- 48 56-528...
  • Page 8 FEATURES OF IG FIDELITY & STEREO FM MODELS SPEAKER C ASSIS CABINET VOICECOIL SIZE PART IMPEDANCE TYPE POWER MODEL STYLE COLOR MODEL NUMBER INC ES (IN O MS) OUTPUT 49- 59 2-4%" Walnut 20AT3 Z 20 T ransistor A589W Table FM/AM/ (Lift Lid) Phono...
  • Page 9 FEATURES OF IG FIDELITY & STEREO FM MODELS RECORD C ANGER OT ER FEATURES REMOTE RECORD INDICATOR NUMBER MOUNTING CARTRIDGE STYLUS NOTE 1 TAPE SPEAKER LIG T STORAGE PROVISION 69-369 Shelf 42- 68 Note 4 Note 8 S-68567 69-372 Shelf 42- 68 Note 4 Note 8...
  • Page 10 FEATURES OF IG FIDELITY & STEREO FM MODELS SPEAKER C ASSIS CABINET VOICE COIL PART SIZE IMPEDANCE TYPE POWER MODEL STYLE COLOR MODEL INC ES NUMBER (IN O MS) OUTPUT 49- 75 2- 0 20 Transistor Pecan 20AT2 Z A93 P Console 49- 094 2-3%...
  • Page 11 FEATURES OF IG FIDELITY & STEREO FM MODELS RECORD C ANGER OT ER FEATURES REMOTE INDICATOR RECORD SPEAKER MODEL MOUNTING CARTRIDGE STYLUS NOTE 1 TAPE LIG T STORAGE PROVISION 69-363 Shelf 42- 68 Note 4 S-68567 69-363 Shelf 42- 68 Note 4 S-68567 69-363...
  • Page 12 FEATURES OF IG FIDELITY & STEREO FM MODELS CABINET C ASSIS SPEAKER VOICE COIL SIZE PART MODEL STYLE COLOR MODEL TY-PE POWER IMPEDANCE NUMBER INC ES OUTPUT (IN O MS) 2- 2 A957P Console Pecan 25AT20 25 Transistor 49- 7 4-3% (Lift Lid) FM/AM/...
  • Page 13 FEATURES OF IG FIDELITY & STEREO FM MODELS OT ER FEATURES RECORD C ANGER REMOTE RECORD INDICATOR NUMBER MOUNTING CARTRIDGE STYLUS NOTE 1 TAPE SPEAKER LIG T STORAGE PROVISION 42- 67 Note 4 69-366 Shelf S-8262 Note 7 69-364 Shelf 42- 67 Note 4 S-8262...
  • Page 14 SECTION 1 SEMI-CONDUCTOR T EORY In order to understand the operation of semi-conductor (solid-state) devices it is necessary to define three terms: conductor, insulator, and semi-conductor. An electrical conductor is a solid substance made up of atoms whose atomic structure contains many excess or “ free ” electrons in the outer orbit.
  • Page 15 When a voltage is connected to a diode as shown in Fig. -3, we have applied Forward Bias. A voltage has been connected in such a way that the junction resistance has been reduced and Forward Current flows in the circuit. FORWARD BIAS CAUSES HIGH FORWARD CURRENT FLOW.
  • Page 16 So far we have seen that forward bias is used to obtain the amperes, until a certain voltage called the breakdown or zener desired forward current and that reverse bias, if of a voltage is reached. At this point, the electrons or “ holes ” sufficiently high value, can result in the destruction of a diode.
  • Page 17 of alternate “ P ” and “ N ” materials in the sequence PNPN as tance of junction J2. With low junction resistance it is now possible for a very small forward voltage to maintain a very shown in Fig. - 0.
  • Page 18 TRANSISTORS Basically a transistor can be considered to be three semi ­ conductor layers consisting of two “ PN ” junctions, which are joined so that the two outer layers are of the same type material, (either “ P ” or “ N ” ). The middle layer is of the remaining material and is normally much thinner (Fig.
  • Page 19 The AC signal voltage to be amplified is applied across RB, Most of the grounded-emitter transistor amplifier circuits, use combined with the DC bias voltage will result in a varying bias an emitter to ground resistor to provide some feedback to across the base emitter junction.
  • Page 20 particular setting of the variable inductance of the oscillator common emitter amplifier circuit there will also be a phase coil establish the operating frequency of the oscillator. Base reversal between input (base of QI) and output (collector of Q2) terminals. circuit resistors of 3.9K and 22K act as a voltage divider to establish the proper base bias voltage for the transistor.
  • Page 21 As gate reverse bias voltage is increased (in the negative increases reverse AGC voltage will increase. This voltage will direction for “ N ” channel FJE.T. ’ s), areas will develop add to the gate bias causing a reduction in drain current (ID) adjacent to the “...
  • Page 23 SECTION 2 MULTIPLEX RECEIVER T EORY A careful study of the block diagram for chassis 29AT24 (Fig. separate RF, Mixer, and Oscillator transistors (Fig. 2-2). A low 2- ) would be most helpful before going into an explanation impedance antenna is used with provisions for connection of a of the operation of current receiver circuit applications.
  • Page 24 IG. 2-3 IG. 2-4 The FM antenna coil (LI), and both the RF input (L2), and advantage of the F.E.T. is that it provides added capabilities in Detector (L3), coils are tuned as well as the Oscillator coil reduction of interference and other undesired signals. AGC (L7) (Fig.
  • Page 25 IG. 2-6 M-A C volt, Gate -9.5 volt and Drain at zero volts. Voltage spread has been provided in the receiver circuitry. The AFC source between Gate and Source terminals is -0.5 volts. The drain voltage is removed from the oscillator circuit when switching terminal is returned to ground via a tap on the FM Detector from FM-AFC to FM, and the oscillator circuit functions coil L3.
  • Page 26 Diode CR20 will be forward biased when in the FM function detected by diode CR202, increasing the negative voltage at and reverse biased in the AM function as a result of the “ B- ” the junction of the 5K and 2.2K resistors (R2 3 and R2 2) supply to the tuner being switched “...
  • Page 27 IG. 2-8 M-AGC the st IF. In this manner we are applying reverse AGC voltage modulated wave at the secondary of T204, the third AM IF to the st IF transistor to reduce its gain and eliminate the transformer, is detected with the resulting wave form having possibility of distortion and overload as a result of excessively the same characteristics as the original amplitude modulation strong RF signals.
  • Page 28 IG. 2-9 AM-AGC IG. 2-10 AM-DETECTOR AND TUNING METER...
  • Page 29 IG. 2-11 M-RATIO DETECTOR station to which we are tuned is also broadcasting 67 KHz store cast material that cannot be allowed to enter the 19K z PILOT AMPLIFIER multiplex detector or distortion will ‘ result, then a very high AND DOUBLER “...
  • Page 30 IG. 2-12 67 KHz TRAP AND COMPOSITE AMPLI IER operate as a full wave unfiltered rectifier, across this secondary will be fed back to the base of the 9KHz amplifier. As this and act as a frequency doubler. The output of this full wave DC voltage increases the conduction of 9KHz amplifier will rectifier is a series of 38KHz DC pulses.
  • Page 31 IG. 2-14 BIPLEX DETECTOR STEREO INDICATOR SWITC emitter will serve as the collector under certain conditions. When switched by a properly applied AC voltage, in push-pull, The stereo indicator switch transistor and the stereo indicator sufficient in value to overcome the cut-off bias normally lamp are in series with a voltage (Figure 2- 3).
  • Page 32 IG. 2-15 BIPLEX DETECTOR WITH THEORETICAL 38 KHz INPUT AND OUTPUT WAVE ORMS through the two load resistors (9. IK and signal passing through via the base of the transistor is 0K) and the secondary winding of T304. The output is taken from across modulated upward and out of the audio range by the 38KHz the emitter and collector of the transistor.
  • Page 33 IG. 2-17 BIPLEX DETECTOR SIGNAL TRACING WAVE ORMS the action of the transistor into two equal amplitude but opposite polarity (L - regular audio signals in the same SIMPLIFIED C ECK OF T E BIPLEX TRANSISTOR and R outputs circuits. The biplex transistor circuit thus acts to reinsert the 38KHz CW (the subcarrier) into the (L - R) A sim P le q ualit y check on the bi P lex transistor can be made as 38KHz side bands and at the same time demodulates this...
  • Page 34 IG. 2-18 UNCTION SWITCH CIRCUIT BOARD Before going into circuit operation, refer to the block diagram through the SCR and the parallel combination of indicator of Fig. 2-20. Audio sources are developed in the conventional lamp DS602 and resistor R64 , causing the lamp to illuminate manner, but each of the six functions has its own control indicating FM operation.
  • Page 35 < <Z) r — £...
  • Page 36 IG. 2-20 UNCTION SWITCH BLOCK DIAGRAM One additional application occurs when in AM. Negative charged C62 to the polarity shown in Fig. 2-22. When the FM voltage from SCR60 ’ s anode is coupled to the base of NPN circuit is “ gated on ” , C62 will discharge via the low resistance transistor Q603, which will hold Q603 at cut-off.
  • Page 37 IG. 2-21 M/AM SWITCH CIRCUITS STEREO/MONO contact will cause either of two actions to occur. If SCR606 is not conducting (MONO), SCR605 will be . triggered “ on ” with a positive gate pulse (Fig. 2-23). Current will flow through resistor R650 and charge C633, developing a positive pulse across it which will be applied via C636 to the gate of SCR606, turning SCR606 “...
  • Page 38 tG. 2-23 STEREO/MONO SWITCH CIRCUITS Transistor Q604 ’ s base voltage will go negative when SCR606 function, negative voltage from the anode of SCR604 is is “ on ” (STEREO). This will cause Q604 to be forward biased applied to CR609 ’ s cathode. The voltage on CR609 ’ s anode and turn “...
  • Page 39 IG. 2-24 TAPE SWITCH CIRCUITS IG. 2-25 PHONO SWITCH CIRCUITS...
  • Page 40 IG. 2-26 PHONO STEREO/MONO SWITCH AND AUDIO PREAMPLI IER CIRCUITS...
  • Page 41 IG. 2-27 EXTENDED BASS SWITCH CIRCUITS right phono audio is connected together via C404 and C454, function. Activating the EXT. BASS circuit causes a positive placing the two stereo signals from the cartridge in parallel, pulse on the gate of SCR607 (which is a momentary action resulting in monaural reproduction.
  • Page 42 IG. 2-28 ZENER DIODE VOLTAGE REGULATOR has started to conduct. Cross-over distortion and the point of ZENER DIODE VOLTAGE REGULATOR conduction are determined by the bias on the output stage. In transistorized circuits it is extremely important that the Many bias circuits only consist of a resistance divider network voltage not vary more than±...
  • Page 43 IG. 2-30 DISTORTION REMOVED BY IG. 2-29 CROSSOVER DISTORTION CLASS AB OPERATION collector of the driver transistor, and the base of the output transistor nearest the high side of the supply voltage. Connect ­ transistor nearest ground. The output circuit design is such ed to this center point are a feedback loop to the pre-driver that there is a center point between the emitters.
  • Page 44 Between the base of each output transistor there is a series When a negative going signal is applied to the driver base connected resistor-diode circuit. Bias voltage is developed current gain of the driver is reduced. At the same time across this resistor-diode combination and controls idling however, the charge on the high value electrolytic will current in the output stage.
  • Page 45 provides a path for these voltages to be applied to the base and battery source, will supply current to the base-emitter circuit. to charge C42 (500 mfd) to almost the supply voltage. There This current will then tend to maintain the collector-emitter will be a small drop in DC voltage between the collector and current at an average value, offsetting the action of the ripple base which will establish the forward bias required for the...
  • Page 46 SECTION 3 FM/AM ALIGNMENT PROCEDURE MUTING CONTROL problem, is to connect an external FM antenna to the receiver. Usually a TV antenna may be available for trial, but even then The muting control which supplies a reverse bias voltage to the the results can be misleading, since many TV antennas are of base of the 9KHz amplifier is factory adjusted, and should...

  • Page 47: Automatic Frequency Control-Afc

    Chassis 20AT21 and 20AT21Z Chassis 25AT20 - Adjust AGC control so that under no signal conditions a voltage of .2 volts is measured across the 820 Micro Volts Forward Input AGC Voltage ohm resistor connected from st IF emitter to “ B- ” (- 2.4V) at Test Point "B"...
  • Page 48 2. When a power transistor is replaced the insulator (when 5. Pencil type soldering iron with a small tip (25 watts or used) between the transistor and the heat sink should also less). be replaced. On chassis 2ZT2 , 2YT23, 2ZT24, 6AT24, 6.
  • Page 49 Because of the wide band pass required in the multiplex FM tuner, it is desirable to use an FM signal generator having a deviation of 400 KHz with a sweep rate of 60 cycles as well as an oscilloscope when aligning both the IF and RF FM portions of this receiver.
  • Page 50 Cx« r> S> < <c v — 4 r — ( r — < r — <...
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  • Page 55 SECTION 4 MULTIPLEX ALIGNMENT PROCEDURE Using the Zenith FM multiplex signal generator, the multiplex To help achieve this IF curve symmetry 0.6 and portion of Zenith or any FM multiplex receiver can be aligned, megahertz markers must be symmetrically positioned and the but first before any attempt is made to do this it is necessary 0.7 megahertz marker must be at the center of the curve.

  • Page 56: Trouble-S Ooting

    The composite signal is very useful since it is an excellent tool 6. Turn generator pilot carrier amplitude control to 5% that can be used in signal tracing the multiplex portion of the position. receiver. We do not recommend that multiplex alignment be 7.
  • Page 57 3. Move the L+R switch from OFF up to L+R and look at the Doubler and Subcarrier Signal Tracing L audio output, and measure the magnitude of the 000 hertz sine wave. If the multiplex detector and proceeding To determine if the doubler is functioning, place your scope at circuitry are aligned properly, the magnitude of the wave the junction of the two diodes and you will see 38KHz DC form at L should be greater than at R.
  • Page 58 SECTION 5 MEC ANICAL ASSEMBLIES Zenith engineers have devised chassis constructions which, while maintaining a compact package size, will provide maximum access to the chassis should service be required. Illustrated here are two chassis configura ­ tions with instructions for tilting sub chassis into working position. C ASSIS 20AT30 AND 20AT31...
  • Page 59 C ASSIS 25AT20...

  • Page 60: Parts List

    PARTS LIST NOTE: Certain circuit boards included in this parts list have component locations identified by item number on the circuit board. These item numbers are also shown on the schematic and in the following parts list — See section 3 for further information. ITEM PART ITEM...
  • Page 61 ITEM PART ITEM PART DESCRIPTION DESCRIPTION Transistor (Pre-Amp) 2 -433 22-3766 .033 MFD Capacitor 50V Dow Coming Heat Conductive Grease (Part Of 205-5 22-2939 680 PF Disc 500V 800-204) RIA) Dual Loudness Control 63-6495 *800-204 Transistor - Output Assembly ( 2 -436) RIB J Wire &...
  • Page 62 PART ITEM ITEM PART DESCRIPTION DESCRIPTION 63-596 2.7 Ohms 0% W R556 49- 52 Speaker (6 ” x 9 ” ) 63-5282 0.39 Ohms 5% 5W R557 - 83 A C Line Cord 63-564 220 Ohms 20% 2W R558 43-5 9 Socket Contact Housing (Phono A C Plug) 63- 820 6.8K 0%54W...
  • Page 63 ITEM PART ITEM PART DESCRIPTION DESCRIPTION 6-32 x /2 Hex Washer Hd. Self-Tap. Screw- 4- 00 *S-8 069 Chassis Bracket Assem. Special (2 used on ea. 2 -398 & 2 -382) *S-8 070 Bracket & Jack Assem. ( 2 required) C ASSIS 9AT27 2 -382 Transistor - Power - Matched Pair (2 required)
  • Page 64 ran i 1 1 tM eivi MAKI DESCRIPTION DESCRIPTION 86-334 Connector Terminal (3 used on 52- 339) 63- 859 56K Ohm Resistor - AW. 0% (2 required) 86-344 Connector Terminal 63- 862 68K Ohm Resistor - ViW. 0% (2 required) 86-389 Connector Terminal (8 required) 63- 876...
  • Page 65 1 1 tivi rwh i 11 tivi KAK 1 DESCRIPTION DESCRIPTION 44-72 Dual Speaker Jack S-770 4 AM Antenna Assembly L 02 Iron Core Sleeve 52- 339 Three Conductor Cable - Phono (Approx. 26 ” ) 49-3 L 03 AM Oscillator Trans. Pri. 52- 442 Four Conductor Cable - Speaker (Approx.
  • Page 66 MAK 1 ITEM 1 1 El VI DESCRIPTION DESCRIPTION 49-368 Iron Core & Spring T202 95-254 AM st IF AM 455 KHz 49-385 Iron Core & Spring T203 95-2547 FM 2nd IF Transformer 0.7 MHz S-62887 FM Oscillator Coil Assem. T204 95-2542 AM 2nd IF AM 455 KHz...
  • Page 67 ITEM PART ITEM PART NO,/ DESCRIPTION DESCRIPTION 470K Ohm 0% VzW 63- 8?t R463 S-79438 Multiplex Input Coil Assem. 200 Ohm 0% J /zW 63- 789 R464 C ASSIS 10ZT31 82bhm 0%y 2 W 65-|MO R465 63- 853 43K Ohm 5% J /zW R466 .05 MFD Disc 25 V 22-3034...
  • Page 68 1 1 EIVI NO. ” DESCRIPTION DESCRIPTION C465 22-3687 Mfd Electrolytic 50V 2 -433 Transistor - Pre-Amplifier (2 required) C467 22-2939 680 Pf Disc 500V Transistor - Driver (2 required) 2 -706 C470 22-4568 00 Mfd Electrolytic 5V Transistor - Output (Matched Pair- 800-270 C472 22-372...
  • Page 69 1 1 LM ITEM PART AK 1 DESCRIPTION DESCRIPTION 63- 876 50K Ohm 0% C4 4 R453 470 Pf Disc 500V 22- 6 R454 63- 883 220K Ohm 0% C4 5 Mfd Electrolytic 50V 22-3687 27K Ohm 0% R455 63- 845 C4 7 680 Pf Disc 500V 22-2939...
  • Page 70 r«n i 1 1 tM 1 1 U IVI KART DESCRIPTION DESCRIPTION Q454 Transistors, Output-Matched Pair 63- 803 2700 Ohm Resistor - V2W. 0% (2 required) 800-270 Q455 , (Consists of one 2 -707 and one 63- 8 7 5600 Ohm Resistor - ^W. 0% (4 required) 2 -708) 63- 834 5K Ohm Resistor - V2W.
  • Page 71 ITEM ITEM PART PART DESCRIPTION DESCRIPTION 560 PF Disc 0% 500V 43-5 9 Socket Contact Housing (Male) 22-548 C2 0 5.5 PF Disc +.25PF500V Nine Contact Housing (Female) 22-3770 43-874 .0 Disc 25V 43-876 Three Contact Housing (Female) 22-3393 C2 2 .8 PF Gimmick 0% 500V Three Conductor Cable - Phono (Approx.
  • Page 72 ITEM PART ITEM PART DESCRIPTION DESCRIPTION 63- 764 330 Ohm 0% y 2 W R3 3 56-426 RoH Pin (Part of S-79746) 470 Ohm 0% /2W R3 4 63- 77 58-3 5 Connector Plug (2 required) 820 Ohm 0% W R3 5 63-6066 6 -222...
  • Page 73 ITEM ITEM PART PART DESCRIPTION DESCRIPTION C457 22-5634 . Mfd 200V Transistor - Comp. AM., 9 KHZ Amp., 38 KHZ 2 -639 C458 22-5056 .02 Mfd 25V Amp. & Stereo Indicator Switch (4 required) . 5 Mfd 200V C459 22-5633 * 2 -762 Transistor C460...
  • Page 74 1 1 tivi KAKI ITEM PART DESCRIPTION DESCRIPTION R407R st I.F. Transformer Coil (AM) 95-254 T202 R407L J > 63-7563 5 OK Dual Loudness Control 95-2547 2nd I.F. Transformer Coil (FM) T203 R408 63- 792 .5KOhm 0%y 2 W 95-2542 2nd I.F.
  • Page 75 ITEM PART ITEM PART DESCRIPTION DESCRIPTION 92-450 Light-Up Bar (20AT2 Z) *57-7 53 Die-Cast Escutcheon (20AT2 ) Light-Up Bar (20AT2 ) 58-3 5 Connector Plug (2 required) 92-45 92-453 Light-Up Bar (Tuning Control) *59- 000 Dial Pointer * 92-465 Dial Crystal (20AT2 ) 78- 8 5 Dial Light Socket &...
  • Page 76 ITEM PART ITEM PART DESCRIPTION DESCRIPTION 680 Ohm 0% W E2 3 63- 778 C306 22-3393 .0 Mfd Disc 25V R2 4 63- 778 680 Ohm 0% y 2 W C307 22-5782 2200 Pf Polystyrene 5% 500V R2 5 63- 8 3 4700 Ohm 0% C308 *22-578...
  • Page 77 ITEM ITEM PART PART DESCRIPTION DESCRIPTION R506 63- 933 3.3 Megohm 20% V2W Q454 I Transistor, Output - NPN ( 2 -7 0) 800-289 *20- 744 FM Antenna Coil Q455 J Transistor, Output - PNP ( 2 -709) *20- 648 FM RF Coil * 2-5 66 Dial Background Mtg.
  • Page 78 ITEM ITEM PART PART DESCRIPTION DESCRIPTION .033 MFD Paktron 0% 00V *S-82434 C409 *22-5883 Drive Cord & Eyelet Assem. .0056 MFD Mylar 00V *S-82435 C4 0 22-5640 Drive Cord & Eyelet Assem. (Pointer) .022 MFD 20% 00V *22-58 4 . MFD Disc 0V C ASSIS 20AT31Z C4 2 22-3652...
  • Page 79 ITEM PART ITEM PART DESCRIPTION DESCRIPTION R302 63- 8 7 5.6K Ohm 0% VzW *S-82 04 AM Antenna Assembly R303 63- 768 390 Ohm 0% J / 2 W L 02 Ferrite Core Sleeve 49-3 R304 63- 803 2.7K Ohm 0% y 2 W L 03 In T 0 AM Oscillator Trans.
  • Page 80 r«n i I 1 U.IVI ITEM PART DESCRIPTION DESCRIPTION *59- 0 7 Dial Pointer (AM) 22-4564 0 MFD Electrolytic 25V *64-288 Shoulder Rivet (4 required) .0 PF Gimmick 500V 22-2720 *76- 902 Tuning Shaft C202 . MFD Disc 25V 22-3254 *78- 866 Dial Light Socket &...
  • Page 81 ITEM PART ITEM PART DESCRIPTION DESCRIPTION 63- 775 560 Ohm Resistor 0% W . MFD Capacitor 50V R3 2 22-5 88 C463 470 Ohm Resistor 0% 54W 500 PF Disc 500V R3 3 63- 77 C464 22-5459 470 Ohm Resistor 0% VaW 25 MFD Electrolytic 5V R3 4 63- 77...
  • Page 82 PART item rAK 1 1 1 Cl VI DESCRIPTION NO ' DESCRIPTION *43- 03 Function Plate Housing L 02 InT 04 st IF Transformer (AM) Primary *434 09 6 Contact Housing (4 required) L 03 In T 04 st IF Transformer (AM) Secondary *46-7249 Control Knob - Loudness, - Treble, - 20-2033...
  • Page 83 ITEM PART ITEM PART DESCRIPTION DESCRIPTION 4-27 6-20 x /2 x /4 Hex Hd. Self-Tap. Screw- *78- 90 Socket & Wire (3 required) Stat. Bronze (4 used on ea. 800- 96) 80-209 Tension Spring 4-344 6-20 x /4 x /4 Hex Hd. Self-Tap. Screw- Tension Spring 80- 40 Stat.
  • Page 84 ITEM PART ITEM PART DESCRIPTION DESCRIPTION €633 *22-5904 . 5 MFD 00V C404 22-3080 .005 MFD Disc 25V C634 *22-5907 . MFD 50V C405 22-3362 560 PF Disc 500V C635 *22-58 5 .056 MFD 00V C406 22-3034 .05 MFD Disc 25V C636 22-56 2 C407...
  • Page 85 ITEM PART ITEM PART DESCRIPTION DESCRIPTION .8KOhm 0% AW 63- 796 3.3 MegOhm 0% ‘ AW R3 6 63- 932 9. KOhm5% ‘ A W 63- 825 R3 7 63- 936 3.9 Meg Ohm 0% AW R6 2 .5K Ohm 0% ‘ AW 63- 792 470KOhm 0% AW R3 8...
  • Page 86 1 1 fcIVI PART rAK i ITEM DESCRIPTION DESCRIPTION R687 63- 932 03- 42 3.3 Meg Ohm 0% YzW CR605 Diode R688 63- 932 3.3 MegOhm 0% W CR606 03- 42 Diode R689 63- 932 03- 42 3.3 Meg Ohm 0% W CR607 Diode R690...
  • Page 87 ITEM PART PART ITEM DESCRIPTION DESCRIPTION *83-7324 Trim Strip (Bottom) 22-4555 Mf Electrolytic Capacitor 0V (2 req.) *83-7325 Trim Strip (Top) .22 Mf Capacitor 00V (2 required) 22-5639 *83-7383 Escutcheon Strip *26- 859 Dial Scale *83-7384 Indicator Strip Log Scale *226- 860 *83-7385 Indicator Strip...
  • Page 88 ITEM PART ITEM PART DESCRIPTION DESCRIPTION 49-370 Iron Core (Part of S-7680 ; *964-22009 Transistor * 85-3 Silicon Control Rectifier (4 required) *964-22009 Transistor * 85-4 Silicon Control Rectifier (2 required) *964-22009 Transistor * 85-5 Silicon Control Rectifier (2 required) *964-22009 Transistor 88- 37...
  • Page 89 ITEM PART ITEM PART DESCRIPTION DESCRIPTION 8 PF Disc 5% 500V 22-3393 .0 MFD Disc 25V 22-248 22-46 3 22-47 8 .00 Mfd Feed Thru Cap. 500V .00 MFD Feed Thru 500V .002 Mfd Feed Thru Cap. 500V 22-45 5 .8 PF Gimmick 500V 22-4729 22-3622...
  • Page 90 rAK l ITtM iicivi DESCRIPTION DESCRIPTION 72- 27 8 x l-% Phillips Flat Hd. Wood Screw-Stat. 54-424 8-32 Palnut (4 Mt. 49- 02) Bronze ( 0 Part of 4-766 ) 57-5204 Nameplate (Part of 4-766 ) 83-4235 Cushioning Strip (Part of 4-766 ) 72- 27 /4 Phillips Fl.
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  • Page 139 20AT21 AND 20AT21Z C ASSIS LAYOUT...
  • Page 140 20AT21 AND 20AT21Z C ASSIS WIRING AND COMPONENTS AS VIEWED FROM FOIL SIDE S-/SW87 FM TUNER ASSEMBLY SC EMATIC...
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  • Page 142 20AT30 AND 2OAT3OZ C ASSIS WIRING AND COMPONENTS AS VIEWED FROM FOIL SIDE...
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  • Page 147 20AT31Z C ASSIS WIRING AND COMPONENTS AS VIEWED FROM FOIL SIDE...
  • Page 148 25AT20 - AUDIO - C ASSIS WIRING AND COMPONENTS AS VIEWED FROM FOIL SIDE 25AT20 - RF-C ASSIS WIRING AND COMPONENTS AS VIEWED FROM FOIL SIDE...
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  • Page 156 ZENIT RADIO CORPORATION 1900 N. AUSTIN AVENUl C ICAGO, ILLINOIS 00639 ’ 4 SPECIFICATIONS SUBJECT TO C ANGE WIT OUT NOTICE PRINTED IN U.S.A. 923-558 F18 RR 6/69 30M...

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