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AM/FM Stereo Tuner

Automatic volume control (AVC) action is obtained by feeding the negative dc voltage

developed at the voltage-doubler detector (D1/D2) back to the grid circuits of V1, V2, and V3. A

filter comprised of R10/C7 and R11/C13 remove audio components from the AVC voltage buss.

The dc output from this network is proportional to the incoming signal strength and so is useful as

a gain controlling voltage. AVC is applied to the grid circuit of V2 from R10/C7. AVC bias for

V1 is taken from the same point but through another filter of R1/C1 to provide isolation between

the two stages. Again, the voltage is applied to the grid through the antenna coil, with signal

return provided by C1. AVC control voltage for the V3 is reduced by the voltage divider R11/R12

and C13. Reduced AVC is desirable in the IF amplifier to keep the stage operating in a more

linear fashion, thus reducing distortion. Because the AVC voltage from the voltage-doubler

detector is approximately twice that obtained with other types, overload is less likely to occur and

audio output variation between weak and strong stations is kept at a minimum.

The transformer-coupled ac input power is converted to dc operating power for the amplifier

stages by rectifier V5, the output of which is delivered to choke L1 and then to the filter bank of

C28 and C29. The capacitors are bypassed with 100 k

, 2 W, resistors to equalize the voltages

across the capacitors and provide a discharge path when power is removed. A B+ voltage output

of about 250 V is provided at terminal #1 for the FM tuner PWB, along with 6.3 V ac at terminals

#3 and #4 for the tube heaters. Zener diodes ZR1 and ZR2 keep the output of the B+ supply below

400 V when no load is applied.

A varistor is placed across the front-panel power switch to minimize transient disturbance

resulting from removal of primary power from the amplifier. Switches normally exhibit some

amount of “contact bounce” when changed from one position to another. This can lead to noise

resulting from the high voltages generated by the collapsing magnetic field of the transformers in

the circuit. The varistor is essentially invisible in the circuit until a predetermined voltage is

reached, at which point the resistance of the device decreases to a low value, thereby shunting the

transient energy. Attention to transient disturbances is critical for proper operation of solid-state

hardware; taking similar precautions in tube-based equipment is a good practice.

Analysis of any design needs to include the impact—if any—on safety should the device fail.

In the case of the varistor, the usual failure mode is a short-circuit. That being the case, if the

varistor failed the user would be unable to turn the tuner off from the front panel. While this is an

Содержание AM/FM Stereo Tuner 2012

Страница 1: ...WhitakerAudio AM FM StereoTuner User and Assembly Manual...

Страница 2: ...itakerAudio Specifications subject to change without notice Any trademarks used in the manual are the property of their respective owners Note This document is intended to assist readers in building a...

Страница 3: ...Printed Wiring Boards 79 5 3 6 1 AM Tuner PWB 79 5 3 6 2 FM Tuner PWB 80 5 3 7Wire the Transformer Leads 82 5 3 7 1 Cable Organization 82 5 3 7 2 Power Transformer Leads 83 5 3 7 3 Choke Leads 84 5 3...

Страница 4: ...nes 139 8 2 FM Section 139 8 2 1Tuning Guidelines 140 9 Troubleshooting Guidelines 142 9 1 Safety Considerations 142 10 Tube Characteristics and Data 144 10 16AL5 144 10 26BA6 145 10 36BE6 147 10 46BQ...

Страница 5: ...ressive industrial design of the other offerings in the WhitakerAudio line This tuner like the other products is limited in number Overview specifications Tube AM FM tuner with mono and FM stereo outp...

Страница 6: ...sponse in order to enjoy the capabilities of the radio stations of the day The AM tuner is capable of flat response up to 9 kHz and with wide range program sources the effect was quite similar to FM o...

Страница 7: ...d therefore offered similar performance figures This tuner is a bit different in that a ratio detector is used The ratio detector is capable of excellent performance and has the advantage of being sel...

Страница 8: ...nent placement and board traces have been engineered to minimize hum and noise The boards feature a unique mounting technique for the vacuum tubes used in each tuner that keeps heat away from the PWB...

Страница 9: ...adio frequency RF coils and transformers Regrettably such devices are no longer manufactured for tube based systems and the choice of new old stock NOS components is exceedingly limited Fortunately th...

Страница 10: ...mpedance straight wire type of antenna to the RF amplifier grid circuit directly through a coupling capacitor A much smaller antenna can be used where necessary but with poorer noise rejection Along t...

Страница 11: ...11 AM FM Stereo Tuner Figure 1 1 Schematic diagram of the AM tuner section...

Страница 12: ...cy that the intermediate frequency IF transformers are tuned This function of changing frequencies is the well known as the Superheterodyne Principle Improved selectivity and gain is obtained due to t...

Страница 13: ...the carrier in some manner usually by employing a non linear unidirectional current device such as a vacuum tube or solid state diode RF energy remaining after detection is removed in a low pass filt...

Страница 14: ...rheterodyne receiver is an exact duplicate of the incoming RF signal the only change being the carrier frequency Carrier and oscillator frequencies are removed at the first IF stage only the differenc...

Страница 15: ...hoke L1 and then to the filter bank of C28 and C29 The capacitors are bypassed with 100 k 2 W resistors to equalize the voltages across the capacitors and provide a discharge path when power is remove...

Страница 16: ...lied to the antenna coil T51 the purpose of which is to match the antenna impedance 300 to the tube input impedance and to tune this input to the FM broadcast band Coil T51 is broad banded to tune the...

Страница 17: ...17 AM FM Stereo Tuner Figure 1 2 Schematic diagram of the FM tuner section...

Страница 18: ...lator frequency is selected so it is always 10 7 MHz higher than the frequency of the RF section Therefore the difference will always be 10 7 MHz It is to this frequency that the intermediate frequenc...

Страница 19: ...entioned and thus cancel A certain amount of unbalance will always be present in the circuit however so some response to noise will be evident when listening to weak signals Audio from the T54 seconda...

Страница 20: ...k and C53 0 01 F This network filters out all RF IF and audio energy preventing interaction between the input and output stages of the tuner The dc voltage developed at the detector output is proporti...

Страница 21: ...esulting composite signal is then demodulated by balanced diode detectors X5l and X52 Since diodes X5l and X52 are connected in opposite directions in the balanced detector circuit a L R signal will a...

Страница 22: ...ilt in California USA Righ Chan Left Chan J C Whitaker AM FM Stereo Tuner Hi Z Loop Gnd Audio Output Neutrix NF2D 0 88 in 0 13 in Center Neutrix NF2D 0 88 in 0 13 in Center Molex 38720 3202 Molex 3872...

Страница 23: ...V trimmer 3 Sprague Good man GYA27000 Mouser 659 GYA2700 0 C3 3 gang variable capacitor 0 100 pF 0 200 pF 0 450 pF 1 Heathkit 26 33 C4 C19 C92 C93 100 pF 500 V disc 4 Cornell Dubilier CD15FD101 JO3F 7...

Страница 24: ...90163 C75 10 F 50 V electro lytic 1 Vishay TE1304 E3 70079649 C82 2 F 450 V electro lytic 1 Vishay TVA1701 E3 70079695 C84 C91 390 pF 500 V disc 2 Cornell Dubilier CD15FD391 FO3F Newark 81K0635 C85 C8...

Страница 25: ...ns 3386F 1 105LF 70154073 R51 R57 6 8 k 2W 2 Ohmite OY682KE 70022236 R54 R80 R83 470 k 0 5 W 3 Ohmite OL4745E 70022936 R55 R60 R87 R92 10 k 0 5 W 4 Ohmite OL1035E 296 1483 R61 330 k 0 5W 1 Vishay VR37...

Страница 26: ...efuse V07E130P 845 0587 FL1 AC line filter 1 Qualtek 848 10 003 689 3564 SW1 Power switch SPST push button 1 NKK Switches WB12T DA 870 0669 SW2 Rotary switch 4 pole 3 position 1 ElectroSwitch C4D0406N...

Страница 27: ...l 1 Heathkit 40 65 L52 Oscillator coil 1 Heathkit 3 turns 14 3 8 in dia tap at 1 turn L53 Mixer coil 1 Heathkit 4 turns 14 3 8 in dia L54 Multiplex oscillator coil 1 Heathkit 40 384 L55 Multiplex 67 k...

Страница 28: ...om Plexiglas trim 1 TAP Plastics custom Top chassis decal 1 FastSigns custom Main chassis 14 in x 17 in x 3 in steel 1 Hammond 1441 38BK3 806 1396 Main chassis base plate 14 in x 17 in steel 1 Hammond...

Страница 29: ...custom C55 circuit shield 4 in by 1 5 in bent 1 25 in from end 1 custom Table 2 2 Consumables for the AM FM Stereo Tuner Quantity Description 2 ft Hookup wire 18 black solid 10 ft Hookup wire 18 gree...

Страница 30: ...4 3 4 inch 4 Phillips head screw 6 3 4 inch 1 Phillips head screw 6 1 inch 10 Nut 6 with captive lockwasher 1 Nut 6 fiber locking 1 Wing nut 6 12 Flat washer 6 6 lockwasher 6 5 Flat washer 3 8 inch 4...

Страница 31: ...ber of interconnecting wires needed for this amplifier expanded sleeving is used where practical to organize the cabling This tends to simplify cable routing and provides for a cleaner appearance Wher...

Страница 32: ...300Vac Plate winding Red T6 300Vac Plate winding Red 600Vct Plate winding center tap Red yellow 6Va 6 3 V heater Green 6Vb 6 3 V heater Green 6Vct 6 3 V heater center tap Green yellow 5Va 5 V heater...

Страница 33: ...The layout of the AM tuner PWB is shown in Figure 3 1 V6pin8 V6 cathode Black C3a Tuning capacitor C3a Yellow C3 C3b Tuning capacitor C3b Yellow C3c Tuning capacitor C3c Yellow Term 1 Barrier strip p...

Страница 34: ...34 WhitakerAudio Figure 3 1 Component layout for the AM tuner PWB...

Страница 35: ...300 antenna input Twinlead L52ct Connection to L52 tap Yellow CONN1 AGC display Shielded audio cable CONN2 Mono audio output Shielded audio cable CONN3 Chassis mounted separation control Shielded aud...

Страница 36: ...36 WhitakerAudio Figure 3 3 Component layout for the FM tuner PWB...

Страница 37: ...While this is perhaps overkill it is instructive to see the variation in component values which measurement before installation will reveal The resistor color code is shown in Figure 4 1 Observe prop...

Страница 38: ...hat will adversely impact the noise floor Efficiently making the socket connections to the PWB requires a bit of practice The recommended procedure is detailed in Section 5 Be certain to wear protecti...

Страница 39: ...uce the possibility of component mix ups Each section heading that follows marks a logical start stop point in construction of the amplifier Do not rush through the project instead consider setting mo...

Страница 40: ...re 29 positions in all Solder in place Note that the mounting pins fit tight into the board This is normal Use a pair of pliers to hold the tab while inserting the pins into the PWB Make sure the PWB...

Страница 41: ...0 5 W Solder in place Install R11 R12 2 2 m 0 5 W Solder in place Find R13 27 k 0 5 W Set this component aside It may be used later Install R17 33 k 0 5 W Solder in place Figure 5 1 Recommended proced...

Страница 42: ...mall screwdriver set the control for the mid point of travel Install VR1 power thermistor 10 cold Solder in place Install VR2 thermistor 20 cold Solder in place Clean the soldering iron tip before pro...

Страница 43: ...Install C21 150 pF 500 V disc Solder in place Install C22 C23 2000 pF 500 V disc Solder in place Install C25 270 pF 500 V disc Solder in place Install C28 C29 100 F 450 V electrolytic Solder in place...

Страница 44: ...onnection positions are color coded These colors match up with the color legends on the board As each device is installed complete the connection between the PWB pad and the respective post on the dev...

Страница 45: ...the mounting hole adjacent to the ground lug from each IF transformer T3 and T4 Place the a lockwasher between the ground lug and the PWB This will space the ground lug above the board and prevent con...

Страница 46: ...ire from the component side through the pad and into the socket soldering tab 2 Crimp in place see Figure 5 2b 3 From the component side pull the wire tight and solder in place 4 Trim the excess lead...

Страница 47: ...the Heater Circuit Wire package and cut two 4 inch pieces of 22 green heater wire Place one piece of heat shrink tubing over one end of each wire Crimp one wire on pin 3 of V1 Solder in place When sol...

Страница 48: ...gh the heat shrink tubing on the lead already connected to pin 3 of V2 Route the wire to the pin and crimp in place Solder keeping the heat shrink tubing away from the hot wires and the soldering iron...

Страница 49: ...rom V3 together and route to socket V5 see Figure 5 2d for placement The wires should be placed at socket level Do not dress the wires against the PWB Trim the wire lengths as needed to comfortably re...

Страница 50: ...n 9 Apply a stream of hot air to shrink the tubing over the pin Be careful to not use too much heat Cut a 2 inch piece of heater wire Slip one end through the heat shrink tubing on the lead already co...

Страница 51: ...te to the H1 and H2 pads on the PWB see Figure 5 2d for placement The wires should be placed at socket level Do not dress the wires against the PWB Trim the wire lengths as needed to comfortably reach...

Страница 52: ...t on one side of the device there are three screw adjustable trimmer capacitors Set the three adjustment screws so they are tight and then loosen each by one turn Set C3 aside it will be installed lat...

Страница 53: ...of the board into the chassis After reviewing the Construction Techniques section of this manual begin populating the PWB As the packing envelopes are used set them aside for recycling Before beginni...

Страница 54: ...Install R89 15 k 0 5 W Solder in place Install R91 220 k 0 5 W Solder in place Install R94 8 2 k 0 5 W Solder in place Install R105 8 2 k 2 W Solder in place providing about 1 4 inch clearance above...

Страница 55: ...0047 F 600 V Solder in place Install C73 C74 C76 270 pF 500 V disc Solder in place Install C75 10 F 50 V electrolytic Solder in place Be certain to observe proper polarity Install C79 C100 C109 0 047...

Страница 56: ...s can be damaged by excessive heat Note that D51 and D52 are located on the matrix daughter board Install the four terminal Molex barrier strip Solder in place Mount the six 4 terminal Molex contact h...

Страница 57: ...in the following step Find C90 1500 pF 500 V disc which was set aside in a previous step Secure one lead to terminal 1 of T55 Solder 2 wires Secure the other lead of C90 to terminal 2 of T55 Solder 2...

Страница 58: ...apacitor to terminal 2 on L55 Solder two wires Route the other lead through the C84 C85 pad on the board Do not solder Find C84 390 pF 1000 V disc which was set aside in a previous step Secure one lea...

Страница 59: ...d install a ground lug on the foil side of the board using the 4 hardware provided Be sure to orient the lug so it does not make contact with any of the traces on the board In the following steps the...

Страница 60: ...the other side Double check your work as you proceed The next task is to make the heater connections to the nine sockets on the PWB The following procedure is recommended Install the 3 post terminal...

Страница 61: ...standoff Loosely twist the wire and the choke lead together and route to the 3 post terminal strip Place the wires above the circuit board at socket level Examine the 3 post terminal strip Numbering...

Страница 62: ...on the terminal strip Solder 3 connections on each post Twist the wires together and route to socket V53 see Figure 5 2d for placement The wires should be placed at socket level Do not dress the wires...

Страница 63: ...ce Solder keeping the heat shrink tubing away from the hot wires and the soldering iron Slide the heat shrink tubing into position at the base of the socket Apply a stream of hot air to shrink the tub...

Страница 64: ...heat shrink tubing on the lead already connected to pin 4 of V56 Route the wire to the pin and crimp in place Solder keeping the heat shrink tubing away from the hot wires and the soldering iron Slip...

Страница 65: ...hould straddle the standoff Twist the green wires to comfortably reach the V58 socket Trim the wire lengths if necessary Place a piece of heat shrink tubing on each wire Connect one wire to pin 4 of V...

Страница 66: ...through the heat shrink tubing on the lead already connected to pin 4 of V57 Route the wire to the pin and crimp in place Solder keeping the heat shrink tubing away from the hot wires and the solderin...

Страница 67: ...wire should extend from the component side of the board Bend the wires 90 degrees so they mate with the pads on the FM tuner PWB Insert the matrix board onto the tuner board To provide for a proper fi...

Страница 68: ...mounting posts From the foil side of the board solder the two terminals of C55 to their respective PWB pads Make certain the solder extends from the connection lugs to the PWB pads Assembly of the FM...

Страница 69: ...69 AM FM Stereo Tuner Set the FM tuner board aside it will be used later b...

Страница 70: ...e chassis and final assembly process is divided into a number of sub sections allowing the builder to proceed at a measured pace A full size image of the completed chassis bottom view is provided Refe...

Страница 71: ...b Bend the tabs on the switch back toward the rear of the device to approximately a 45 degree angle This will facilitate connection of the terminals and avoid contact with power switch SW1 Place the l...

Страница 72: ...Reinstall the red pointers on the two planetary reduction drive shafts The orientation of the pointers is not important now they can face in any direction Install the tuning control knobs Using an al...

Страница 73: ...rcuit breaker CB1 using the hardware provided Position the device so the number rating is oriented sideways at a 90 degree angle to the top of the chassis This will provide adequate clearance for rela...

Страница 74: ...8 Note the locations of the cable clamps Find the cable clamp hardware package There are four sets in the package Install using the hardware provided Orient the cable clamps as shown in Figure 5 8 Th...

Страница 75: ...r Input Circuit Breaker AC Power Built in California USA J C Whitaker Stereo FM AM Tuner Neutrix NF2D 0 88 in 0 13 in Center Neutrix NF2D 0 88 in 0 13 in Center Molex 38720 3202 Molex 38720 3202 Molex...

Страница 76: ...and FM tuner PWB There are two mounting holes within the chassis space occupied by the power transformer These holes will be inaccessible after the transformer is installed Using 4 counter sunk screw...

Страница 77: ...base of the potentiometer Place the lockwasher provided on the shaft and insert the device through the mounting hole Note that R24 is located closest to the back panel on the AM tuner side of the chas...

Страница 78: ...ecure the position of the device to prevent accidental movement Place the locking nut on the shaft finger tight Mount R102 10 k potentiometer FM Left Channel Gain Control Note the tab extending from t...

Страница 79: ...eyelet off of the far end of each ground lug Bend each lug upward in a U fashion Temporarily install C3 on the tuning shaft Temporarily place the AM tuner PWB in position in the chassis The board wil...

Страница 80: ...the PWB Do not tighten the screws until all screws have been threaded and the sockets properly extend through the chassis cutouts so they are flush with the top of the chassis The AM tuner PWB has now...

Страница 81: ...tandoffs at the corners of the PWB Do not tighten the screws until all screws have been threaded and the sockets properly extend through the chassis cutouts so they are flush with the top of the chass...

Страница 82: ...ut two 4 inch pieces of large expandable sleeving Cut four pieces of large heat shrink tubing each about 3 4 inch long Feed one 4 inch piece of large sized sleeving onto each set of the leads from the...

Страница 83: ...neutral to T6 Find the white lead from the power transformer Install a connector to the wire Attach to the AC N2 post on the AM tuner PWB Connect AC H3 AC hot to T6 Find the gray lead from the power t...

Страница 84: ...to a lead gently pull on the wire and terminal to make sure a good crimp has been made Connect L2in choke in Find one of the black wires from the power supply choke L2 Install a connector to the wire...

Страница 85: ...pieces of small heat shrink tubing over each wire and push town to cover the socket terminals Process with the heat gun Twist the green wires together Cut one 4 inch piece of small sized expandable s...

Страница 86: ...tall the miniature quick disconnect connectors provided with the relay Note that these two connector types are not interchangeable Twist the wires together Attach the white twisted pair miniature conn...

Страница 87: ...e on each end of the cable Process with the heat gun This cable will be used to connect the back panel AM tuner input terminals to the AM tuner PWB Use one end of the shielded cable to make the follow...

Страница 88: ...ce of twinlead Connect one end of the cable to the ANT pads on the FM tuner PWB Solder Connect the other end of the cable to the FM antenna barrier strip terminals on the back panel Solder The front p...

Страница 89: ...ded cable Attach Molex connector pins to each of the four wires including shield on one end of the cable Insert the connector pins into the socket housing as follows red to position 1 white to positio...

Страница 90: ...R86 attach the wires from the cable as follows black to terminal 1 low white to terminal 2 arm and red to terminal 3 high Solder Clip off the drain wire it is not used on this end Dress the cable agai...

Страница 91: ...the audio cable Process Insert the Molex socket into the Conn4 Left Gain connector on the FM tuner PWB Note that the drain wire goes to the last ground position Route the cable to the rear of the cha...

Страница 92: ...n completed Note that while the connectors of the power cord receptacle are recessed it is nonetheless possible to make contact with hot connectors if the socket is probed For this reason do not leave...

Страница 93: ...black wire from FL1 Load Solder the wire to one of the SW3 terminal posts Prepare one 14 inch long 22 black wire Cut a 1 2 inch long piece of small heat shrink tubing and slip it on the wire Solder t...

Страница 94: ...B Interconnections In the following steps the necessary connections will be made between the AM and FM tuner PWBs Cut a 12 inch long 22 red wire Attach a spade terminal to one end of the wire Connect...

Страница 95: ...erminal and 4 terminal on the FM tuner PWB barrier strip Bend the barrels up slightly to facilitate installation of the terminals Position the interconnecting cable above the bank of electrolytic capa...

Страница 96: ...e to position 2 Cut two short pieces of heat shrink tubing each about 3 4 inch long Place the tubing at each end of the audio cable Process Insert the Molex socket into the Conn2 Tuner Audio Output co...

Страница 97: ...switch using the available cable clamp alongside the FM tuner PWB Leave the end free for now It will be connected later Prepare a 31 inch audio cable Cut two short pieces of heat shrink tubing each ab...

Страница 98: ...the audio output functions Note that in order to access all necessary pins on switch SW2 it may be necessary to loosen the mounting nut and rotate the switch in one direction or another After all con...

Страница 99: ...the connector pins into the socket housing as follows for wire one shield to position 1 white to position 2 for wire two white to position 3 shield to position 4 Place a mark using a pen or magic mar...

Страница 100: ...e as it will not be used Cut a 2 inch 22 white wire Connect one end to position 2 on SW2c Solder 2 wires Connect the other end of the white wire to position 3 FM on SW2c Solder Organize and clean up t...

Страница 101: ...101 AM FM Stereo Tuner Figure 5 11 Chassis view of the AM FM Stereo Tuner...

Страница 102: ...102 WhitakerAudio Figure 5 12 Detail views of the AM FM Stereo Tuner a FM tuner PWB b AM tuner PWB c AM tuner variable capacitor d FM front end with shield in place e AM rod antenna a b c d de...

Страница 103: ...further Recheck all primary connections 4 Measure the resistance between the line terminals of the ac cord It should be a high value with the front panel power switch Off due to VR3 typically greater...

Страница 104: ...cuit 6 22 k Varies due to filter capacitors in circuit 7 68 V4 12AU 1 62 k Varies due to filter capacitors in circuit 2 1 m 3 2 2 k 4 Heater 5 Heater 6 17 k Varies due to filter capacitors in circuit...

Страница 105: ...r capacitors in circuit 7 Infinity 8 Infinity 9 Not connected V52 6U8 1 25 k Varies due to filter capacitors in circuit 2 1 m 3 120 k Varies due to filter capacitors in circuit 4 Heater 5 Heater 6 18...

Страница 106: ...2 Not connected 3 Heater 4 Heater 5 65 K Same as pin 1 6 1 m 7 1 k V57 12AU7 1 70 k Varies due to filter capacitors in circuit 2 470 k 3 1 5 k 4 Heater 5 Heater 6 12 k Varies due to filter capacitors...

Страница 107: ...dvised If possible first apply power using a variable voltage ac supply In that way the voltage can be brought up slowly while monitoring the current drawn from the line If a short circuit exists in t...

Страница 108: ...t adjust while power is applied 15 Using extreme caution check for proper voltages at the tube connection points listed in Table 6 2 All voltages are measured with respect to ground except as noted us...

Страница 109: ...9 heater 6 225 V 7 0 V 8 0 V 9 6 3 V ac Measured with respect to pin 4 or 5 heater V5 6CA4 1 300 V ac 2 0 V 3 270 V 4 6 3 V ac Measured with respect to pin 5 heater 5 6 3 V ac Measured with respect t...

Страница 110: ...5 6 3 V ac Measured with respect to pin 4 heater 6 260 V 7 0 V 8 0 V 9 0 V V53 6CB6 1 0 V 2 0 V 3 6 3 V ac Measured with respect to pin 4 heater 4 6 3 V ac Measured with respect to pin 3 heater 5 260...

Страница 111: ...V V57 12AU7 1 250 V 2 0 V 3 0 V 4 6 3 V ac Measured with respect to pin 9 heater 5 6 3 V ac Measured with respect to pin 9 heater 6 260 V 7 0 V 8 0 V 9 6 3 V ac Measured with respect to pin 4 or 5 he...

Страница 112: ...put switch to AM 21 Connect the ac line cord and switch the power on Observe the tubes for any signs of overheating or other unexpected behavior The filaments should be lit Remove power if any problem...

Страница 113: ...operates In order to optimize performance of the tuner it will be necessary to perform a complete alignment That will be discussed later Possible problems at this point include no output or oscillati...

Страница 114: ...spect to pin 4 heater 4 6 3 V ac Measured with respect to pin 3 heater 5 210 V 6 90 V 7 0 7 V V4 12AU 1 100 V 2 0 V 3 4 V 4 6 3 V ac Measured with respect to pin 9 heater 5 6 3 V ac Measured with resp...

Страница 115: ...d with respect to pin 5 heater 5 6 3 V ac Measured with respect to pin 4 heater 6 155 V 7 55 V Subject to wide variations 8 85 V Subject to wide variations 9 0 V V52 6U8 1 95 V 2 1 4 V 3 80 V 4 6 3 V...

Страница 116: ...ons V56 6C4 1 60 V 2 0 V 3 6 3 V ac Measured with respect to pin 4 heater 4 6 3 V ac Measured with respect to pin 3 heater 5 60 V 6 0 V 7 1 65 V V57 12AU7 1 60 V 2 0 V 3 1 6 V 4 6 3 V ac Measured with...

Страница 117: ...d when the grid of the stage is contacted If a point is found where no response is obtained the defective stage has been identified and checking can be concentrated there Response all the way through...

Страница 118: ...ange of 3 to 6 V dc An effective way of checking for proper operation of the FM LO is to use a frequency counter capable of measuring at least 110 MHz Most frequency counters in this range have suffic...

Страница 119: ...mproper alignment or a poor antenna installation if the tuner is receiving distant stations Oscillation can cause excessive noise in the receiver as can a defective tube In some cases 60 Hz frequency...

Страница 120: ...t all filter capacitors fully discharge When instructed to switch the receiver on allow at least 60 seconds for warm up and stabilization before taking measurements or making adjustments An aluminum s...

Страница 121: ...it does not substantially alter the response of the IF system at various dial setting Sharp attenuation at 10 kHz is required to reduce the audio heterodyne produced when the carriers of two adjacent...

Страница 122: ...teps to assist in alignment of the AM tuner These voltages are as displayed at the generator without a characteristic 50 load Since the metering usually assumes a 50 load the indicated voltage is abou...

Страница 123: ...me over a spread of 19 kHz making it impossible to find the proper peak response Connect the signal generator ground lead to the chassis and the output lead through a 0 01 F capacitor to V2 pin 7 Use...

Страница 124: ...immer adjacent to the middle section of C3 C3c Set the generator and tuner to 1400 kHz and rock the tuner dial to find the maximum response Adjust the C8 mixer trimmer for maximum indication C8 is the...

Страница 125: ...duce about 4 V of AVC typically 0 07 mV rms or so when properly tuned Tune the generator and tuner to 600 kHz Rock the tuning dial for peak indication Adjust the T1 antenna coil slug for peak output R...

Страница 126: ...amplifier to the left and right output RCA connectors on the back panel Tune in a strong local station Note that the tuning eye should be closed or nearly so Connect an audio voltmeter to the right ch...

Страница 127: ...s displayed at the generator without a characteristic 50 load Since the metering usually assumes a 50 load the indicated voltage is about half the actual voltage at the output terminals when working i...

Страница 128: ...n and allow a minute or so to warm up Adjust the bottom slug of T54 Reduce the output of the generator to keep the measured voltage at Test Point A to be about 1 5 V When properly adjusted a generator...

Страница 129: ...AGC line Switch the tuner off and disconnect the hot lead of the signal generator from pin 1 of V53 Temporarily remove the aluminum shield over the front end circuits Connect the generator output thr...

Страница 130: ...into alignment If so the following steps are recommended Set the front panel tuning control to 106 MHz Tune the frequency generator across its operating band until the AGC voltage indicates the prese...

Страница 131: ...Although it is quite difficult to accurately measure the overall frequency response of the FM tuner without specialized test equipment the typical response of a properly aligned tuner of this type is...

Страница 132: ...of D51 D52 R92 R94 Test Point C Set the signal generator to 19 kHz confirm with a frequency counter if available Adjust the generator output level to 0 1 V rms Switch the tuner on Adjust L54 for maxi...

Страница 133: ...o 0 1 V rms Switch the tuner on While monitoring the frequency counter and voltmeter adjust L54 so the displayed frequency is as close to 38 00 kHz as possible While making this adjustment the output...

Страница 134: ...the Channel Separation control to center of travel Connect an antenna dipole or wire antenna to the FM input terminals on the back panel Connect an amplifier to the left and right output RCA jacks on...

Страница 135: ...y 10 dBm on normal program material Note that R102 is accessible from the top of the chassis 7 3 Final Touches Alignment of the AM FM Stereo Tuner has now been completed The final construction steps a...

Страница 136: ...to protect the tubes from users and users from the tubes It also aids cooling somewhat by creating a chimney effect that collects cool air from the edges of the chassis and exhausts heated air from ar...

Страница 137: ...his feature can be helpful if an undesired strong signal from a station causes interference with the station tuned It is possible to null out or substantially reduce the interference by rotating the a...

Страница 138: ...uctor shielded cable Remove insulation and the foil shield from about 1 5 inches of the ends Cut three 3 inch lengths of heat shrink tubing Slide the tuning onto the cable Connect the white wire at on...

Страница 139: ...loop and the 3 ft cable Process Be careful to not use too much heat Connect the loop antenna to the AM input terminals as follows Black Shield to terminal 1 Ground White to terminal 2 Loop 8 1 2 Tunin...

Страница 140: ...especially for FM operation and installing it as high above the ground as conveniently possible Conventional TV antenna grounding and lightning protection devices should be used for safe operation For...

Страница 141: ...stortion on loud passages of music will be noticed if improperly tuned Although virtually all FM broadcasts today are stereo improved sound reproduction may be experienced with the FM mono position fo...

Страница 142: ...t the more obvious symptoms will be corrected In high voltage power supplies look for signs of loose connections and overheating Do not overlook the possibility of tube failure Tubes can fail in unpre...

Страница 143: ...m solder splashes cleaning chemicals and other unexpected events When trimming the leads of a component be careful to hold the excess length so that when cut the lead does not fly towards the face Tab...

Страница 144: ...igure 10 1 Selected tube parameters are listed in Table 10 1 Table 10 1 Key Parameters of the 6AL5 General Characteristics Heater ac dc 6 3 V 0 3 A Peak heater cathode voltage 330 V max Direct interel...

Страница 145: ...Grid 1 to plate 0 0035 pF Grid 1 to cathode heater grid 2 grid 3 and internal shield elements 5 5 pF Plate to cathode heater grid 2 grid 3 and internal shield elements 5 pF Maximum Ratings Design Maxi...

Страница 146: ...that the screen grid input is within the boundary of the operating area on the chart at the selected value of screen grid volt age to be used When a voltage dropping resistor is used the minimum value...

Страница 147: ...ol an available control grid bias voltage of approximately 50 V is typically required The exact value depends on the circuit design and operating conditions The screen voltage may be obtained through...

Страница 148: ...re diagrammed in Figure 10 6 Ek is the voltage across the oscillator coil section between the cathode and ground Eg is the oscillator voltage between the cathode and grid Table 10 3 Key Parameters of...

Страница 149: ...ance2 Unit 1 Unit 2 Grid to plate 1 2 pF 1 2 pF Grid cathode heater and internal shield 2 6 pF Cathode to grid heater and internal shield 5 pF Plate to cathode heater and internal shield 1 2 pF Plate...

Страница 150: ...resistance approx 5900 Transconductance 6400 mhos Plate current 9 mA Grid voltage approx For plate current of 100 A 6 5 V For plate current of 10 A Maximum grid circuit resistance 500 k Notes 1 This...

Страница 151: ...interelectrode capacitance unshielded Grid to plate 1 6 pF Grid cathode and heater 1 8 pF Plate to cathode and heater 1 3 pF Class A1 Amplifier Maximum Ratings Design Maximum Values Plate voltage 300...

Страница 152: ...000 V Peak plate current per plate 450 mA AC plate supply voltage per plate rms with capacitive input filter 350 V Average output current 150 mA Peak heater cathode voltage 500 V Typical Operation wit...

Страница 153: ...ments 6 5 pF Plate to cathode heater grid 2 grid 3 and internal shield elements 2 pF Class A1 Amplifier Maximum Ratings Design Maximum Values Plate voltage 330 V Grid 3 suppressor grid positive value...

Страница 154: ...0 V Target voltage Maximum value 250 V Minimum value 125 V Typical Operation Plate and target voltage 200 V 250 V Series triode plate resistor 1 m 1 m Target current1 for zero triode grid voltage 3 mA...

Страница 155: ...s mounted between the cathode and target When the potential of this electrode is less positive than the target electrons flowing to the target are repelled by the electrostatic field of the electrode...

Страница 156: ...F Plate to cathode heater grid 2 grid 3 internal shield 2 6 pF Direct interelectrode capacitance approx other Triode cathode to heater 3 pF Pentode cathode pentode grid 2 internal shield 3 pF Pentode...

Страница 157: ...ube parameters are listed in Table 10 10 Amplification factor 40 Plate resistance approx 200 k Transconductance 7500 mhos 5000 mhos Plate current 13 5 mA 9 5 mA Grid 2 screen grid current 3 5 mA Grid...

Страница 158: ...ltage 330 V Cathode current 22 mA Plate dissipation each plate 2 75 W Plate dissipation both plates 5 5 W Characteristics Plate voltage 100 V 250 V Grid voltage 0 V 8 5 V Amplification factor 19 5 17...

Страница 159: ...159 AM FM Stereo Tuner...

Страница 160: ...WhitakerAudio AM FM StereoTuner...

Страница 161: ...of parts is placed in a resealable clasp type envelope with a self adhesive label applied Labels such as Avery 5260 are useful for this purpose Recommended envelopes include the following 2 25 inch b...

Страница 162: ...B 7 pin tube socket quantity 3 AM Tuner PWB R29 R30 R32 R34 R36 100 k 2 W AM Tuner PWB VR2 Thermistor 20 cold AM Tuner PWB 9 pin tube socket quantity 2 AM Tuner PWB R33 330 2 W AM Tuner PWB T1 Antenna...

Страница 163: ...FM Tuner PWB R74 R82 47 k 0 5 W FM Tuner PWB C52 C58 C62 47 pF 400 V disc FM Tuner PWB C75 10 F 50 V electrolytic FM Tuner PWB R58 R68 R85 22 k 0 5 W FM Tuner PWB C73 C74 C76 270 pF 500 V disc FM Tun...

Страница 164: ...PWB L51 RF amplifier coil FM Tuner PWB R54 R80 R83 470 k 0 5 W FM Tuner PWB V53 V54 6CB6A tube FM Tuner PWB L52 Oscillator coil FM Tuner PWB R86 R99 R102 10 k 2 W potentiometer chas sis mount FM Tuner...

Страница 165: ...2 Chassis CB1 Circuit breaker 2 A Chassis Main chassis baseplate 14 in x 17 in steel Chassis Power cord Chassis RYL1 5 V dc relay contacts 240 V ac 30 A SPDT Chassis Back panel overlay Chassis AC pow...

Страница 166: ...ser Manual Mounting hardware for V6 Chassis Chassis bottom shield Chassis FM RF shield assembly Chassis SW3 Over temperature switch Chassis 9 pin tube socket shields quantity 2 Chassis C55 shield asse...

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