SERVICE MANUAL - Early Television Foundation
Contents
1. 8 100 to 500 ohms iw R 9 0 5M iw R 10 1K iw R 11 19K lw 12 20 2w VARIABLE RESISTORS 1 2K 2 2K V R 3 50K 4 20K VALVES 1 A C 2 H L Mazda V 2 2 D 4 A Mullard V 3 41 Cossor 4 U R 1 C Mullard V 5 2 D 4 A Mullard V 6 41 M P or AC P Mazda CATHODE RAY TUBE T 18 Cathovisor Type 12 M W 2 T 20 9 M W 2 18 AND T 20 TIME BASE COMPONENT VALUES SECTION 14 35 4020 CONDENSERS T Tubular E Electrolytic 01 mfd C 2 01 mae 001 C4 025 T C 5 50 E C 6 0 5 we s C7 0 5 e i C 8 deleted C 9 0025 mfd 2000 v w C 10 8 120v w 11 8 120 E 12 8 450 E C13 8 450 COILS 1 1 Line Scan oscillator transformer primary L 2 Line Scan oscillator transformer secondary L 3 Line Deflector coil on C R T LA 5 1 5 Shift coil on Frame deflector Yoke L 6 E 2 L 7 Frame deflector oscillator transformer primary L 8 Frame deflector oscillator transformer secondary L 9 Shift Choke L 10 Focus Coil POWER LEAD Power Lead terminated with 6 way Carr Plug and separate Earthing Plug 18 AND T 20 VISION COMPONENT VALUES SECTION 14 2 55 MIS R SERVICE MANUAL RESISTORS K X by 1000 W Wattage 75ohms iw R 2 7 5K R 3 5K i2. 00 cal SWITCHON RI CHASSIS SOCKETS ON CHASSIS This diagram to be used in con junction with T 18 sound diagram C20 on Section 12 3 additional components R 32 100K 1 w 33 250 5 8 D P C O Switch 37 on Section 12 3 deleted when used for T 21 R RI2 58 RADIO GRAM 35 60 SECTION 10 4 SERVICE TUBE AND TIME BASE SECTION II 1 BAIRD ADJUSTMENTS T 18 T 20 T 21 35 4020 Method and Sequence of Adjustments in Setting up Cathovisor C R Tube HEATER ADJUSTMENT Insert A C ammeter in series with Heater lead and connection socket on base of C R Tube and adjust C R Tube Heater resistance on power pack until meter reads 2 5 amp When making this adjustment ensure that a short lead capable of carrying the current is used as 2 amp can easily be lost in a bad or frayed connection a long lead or a meter with a high resistance and under such conditions the reading would appear correct but C R T heater would be overrun when meter leads are removed thereby reducing the life of the tube FOCUS ADJUSTMENT SPOT Ensure that C R T neck is in centre of focus coil by adjusting paxolin locating disc on focus support bracket Reduce Brightness and Contrast to minimum and remove Line and Frame scan generator valves V 3 and V 6 Insert 7K 4 watt resistor between V 3 anode and earth This
3. coil Inductance tuned R F Band Pass Anode Coil 2 Inductance tuned R F Band Pass V 3 Coup ling Coil R F Band Pass V 3 Diode Coil Inductance tuned R F Choke V 4 Grid R F Choke Heater supply V2 V 3 R F Choke Heater supply V2 V 3 R F Choke V4 Anode R F Choke V4 Auxiliary Cathode VALVES Vi V2 V4 TSE4 Mullard TSE4 Mullard DI Mazda TSE4 Mullard BAIRD SERVICE 18 AND 7 20 VISION AND TIME SECTION 14 3 MANUAL BASE CIRCUIT DIAGRAMS 35 4020 VISION DIAGRAM POWER PLUG VIEW LOOKING AT PINS TO SOUND RECEIVER 35 6006 TIME BASE DIAGRAM GREEN G R2 FOCUS COIL SHIFT 2 enore LIO R5 C4 5 19 R4 LINE SCAN TRANSFORMER 2 B c3 o SYNC 18 INPUT a E RIO CIO POWER PLUG VRZ VIEW LOOKING AT PINS LINE LOCK CHASSIS FRAME LOCK FOCUS 35 6007 BAIRD SERVICE T 20 POWER PACK AND SOUND SECTION 15 1 MANUAL COMPONENT VALUES 35 4020 RESISTORS CONDENSERS M Megohm T Tubular K X by 1000 E Electrolytic Wie Cl 25PF C 2 01 mfd T C3 001 mfd R 2 150 ohms aw CA 50 P F ROS 50 K iw C 5 50 P F R 4 20 2w C 6 50 P F dM de 100 P F 8 0 1 mfd T od 1 01 mfd T 7 100K iw 10 01 mfd T R 8 100 ohms iw 11 50 R 9 100K
4. 11 1 INO 1102 S201 7 133205 TYO Ol QV11 NOILVINGOW 1109 0201 811425 INI 51102 121144 INN LINN NOISIA dV2 1QONV SECTION 10 3 35 4020 T 20 POWER PACK AND SOUND UNIT BAIRD avil SNIVW UIMOd 15 8 3 11 403 134206 WIWYOISNVUL 133205 YISNIGNOD 20 TINVd 40123135 JOVLIOA 3131193 AOOO G dWVS 2 OI 135 4 1 NINNL QN 5193 YILVIH 142 ONIN flos TOULNOD INOL 3503 SNIVW TOULNOD 51 1 119206 N3MOd 3SVE 3WIL cya SENI ae 191 331411930 134205 313MOd NOISIA ADNINOIUI HHL OV SYISNIANOD ONIHLOOWS 21141031211 d avail LINDOS IYVdS JAONY YIWYOASNVUL 31 PS vill ldWv 171 51 9 30121110 2 7991 WIWAOISNVUL SNIVW 131205 104100 PYN3d 18 20 T 21 SCAN COMPONENTS T 21 SOUND SERVICE BAIRD wanuat CIRCUIT MODIFICATIONS 35 4020 LINE DEFLECTOR COILS 13814 FOCUS COIL LIO LLL LLL ce L7 OUTER 8 18 INNER 35 6009 Pm VRI CMOUNTED ON CABINET FRONT IN SCREENINO CAN 2 552250251152 pu qo TT AC MAINS 3 PIN PLUC INPUT MAINS DiSTRIBUTNLO 3 PIN SOCKET PANEL ON CABINET MAINS AERIAL LEAD m
5. Primary L25 250 ohms D C resistance of O P Trans Sec L26 0 3 Speech Coil Impedance 2 ohms L S extension is in parallel with L 26 transformer is quired POWER SOCKET Power Sockets 6 way Carr Aerial Sockets 2 way Carr BAIR SERVICE 18 SOUND AND POWER PACK SECTION 12 2 MANUAL COMPONENT VALUES COILS VALVES L 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 1 10 L 11 1 12 1 13 L 14 L 15 L 16 1 17 1 18 L 19 1 20 1 21 1 22 1 23 1 24 1 25 1 26 1 27 1 28 1 29 1 30 1 31 1 32 L 33 L 34 L 35 L 36 L 37 S W Aerial Coupling Coil VI S W Tuning 25 V2 M W Coupling V3 M W Tuning V4 L W Coupling V5 L W Tuning V6 Tel Coupling V7 Tel Tuning Coil Tel Tel Coupling Coil S W Oscillator Secondary Coil LAMP S W 2 Primary hs 35 4020 or Mullard VP4B 2D4A SPAB PEN B4 E HVR2 1W4 350 M W Osc Secondary Flame Lamp 240v 15 w Orange M W Primary i Secondary Primary 2 465 K C Ist I F T Primary Coil PILOT LAMP Secondary Coil 6 2V Tel Oscillator Secondary Coil nr Primary m Tel 2 5 mcs Ist LF Coil 465 K C 2nd I F T Primary Coil MAINS FUSE Secondary Coil Tel 2 5 mcs 2nd I F Coil 3 Amp L S O P Transf Primary Secondary E H T Mains Transf Primary Rect winding 3 200V E
6. and cathode to anode this circuit arrangement increasing the efficiency of the generator The diode cathode being at V 3 anode potential a U R 1 C valve with 20v heater is used as this valve has high voltage insulation between heater and cathode FRAME SYNCHRONISING Synchronising pulses are fed from V 1 anode via resistor R 4 and line pulses filtered from the circuit by R 5 and C 4 which two components form a resistance capacity filter The filtered 50 cycle pulses are coupled via diode valve V 5 which injects frame pulses on to frame scan generator valve grid V 6 FRAME SCAN GENERATOR CIRCUIT Electromagnetic principle is also employed for frame deflection V 6 valve and oscillator transformer coils L 7 and L 8 form an oscillatory circuit coils L 7 L 8 being integral with the deflector yoke A linear 50 cycle sawtoothed current waveform is developed in L 8 winding of the frame yoke which deflects the beam vertically at frame speed The speed is controlled by V R 2 and the amplitude by preset control V R 4 A magnetic shift is introduced to counteract the magnetic deflection caused by the direct current flowing in the anode winding L 7 by passing this same current through shift coils L 5 and L 6 which are also assembled on the frame yoke but arranged electrically in opposition to L 7 The shift choke L 9 prevents resistance loading of the oscillator circuit CATHODE RAY TUBE The construction of the Baird Cath
7. BAIRD SERVICE MANUAL MODELS T 18 T 20 T 21 SECTION 10 1 35 4020 T 18 POWER PACK AND SOUND CHASSIS SERVICE BAIRD SNIGE 009 6 15 31 3 1503 SNIVW WIWWOISNVUL AOOO WISNIGNODAOOOS PZO ONU WIV SNIVW 34 13 SNIVW 31411239 YMI S Z OL 135 JONVISISTY UILVIH TWO UA TdWV 133205 TUVAS SS3N1HOTWd 7 3 YANO NOISIA Wu SRC MCA LIDOS 1Vhi3Y GNNOS V15N10NOO ONIHLOOWS 132205 KEJ 19005 W3MOd sn EL 0V31 Y3IN3H A d SYIHIN 9 30123130 YISNJONOD D F L sio st anos 9 s 4 31 40005 a WIITaWY 3I YIWYOISNVYUL SNIVW 1102 5 FATWA LNdLNO v8 Nid MOD WIV 15 0 0 YIONVHD ADNINO IU VEHI 31 9945 4WV1 10114 9 AT8WiSsV 31 25 T 18 AND T 20 TIME BASE AND SECTION 10 2 VISION DECK SERVICE BAIRD MANUAL 35 4020 SHOWING 20 9M W 2 CATHOVISOR TUBE IN POSITION QV31 YIMOd YIWYOISNVUL NVOS INIT JGOId DUN 341O0HO 141 SUOLVYANIO 3SV8 3WIL 3901 AVU IGOHIVD IAOHLVD 1009 lt 6 HONAS 1 22 30014 HINAS INIT TOULNOD JGNLITdWY ed
8. Double diode second detector A V C rectifier and triode amplifier V 4 PEN A4 Pentode output valve The television radio frequency sound signal is fed through vision and coupled to tuning coil L 2 with coupling coil L 1 The aerial feed from the vision unit is terminated in a non reversible two pin plug and must be connected to the appropriate socket on the L 1 L 2 coil see Section 10 3 which is connected to the grid of frequency changer valve V 1 V 1 amplifies the signal and converts to of 2 5 megacycles The triode portion of V 1 and coils L 4 L 5 form the oscillator circuit which is tuned by T C 2 and external pre set T C 5 LF amplification is given by and 2 L 6 The double diode portion of V 3 rectifies I F signal for audio amplifica tion and A V C LF signals from V 2 anode are rectified by V 3 then applied to V 2 grid via R 6 R 5 giving A V C in the I F amplifier circuit Modulation voltages developed across diode load resistances R 9 and R 10 are coupled via C 14 and V R 1 volume control to the grid of V 3 first stage audio amplifier From V 3 anode C 17 couples the signal to the grid of V 4 pentode output valve Tone control C 16 V R 2 is connected between V 3 anode and earth A special switching arrangement permits the use of television sound only see Vision Unit Summary LOUDSPEAKER A special Rola loudspeaker with 300 ohm field winding and output transformer to match
9. H T Second ary Winding 4v 20amp Heater Winding for Vis T B and Sound 20v winding for U R 1 C V 4 Time Base C R Tube Heater winding 4 volt winding for 1W4 350 Rectifier VJ H T Secondary 330 0 330 Mains Transformer Primary Smoothing choke 0 3 Amp Bulgin Continued overleaf BAIR SERVICE 1 18 POWER PACK AND SOUND SECTION 12 3 MANUAL CIRCUIT DIAGRAM 35 4020 ANODE EARTH SOCKET CRT HEATER 9 TIME BASE POWER SOCKET ns 6 56 GANGED 2130 D 131 20v 55 2132 VR5 WERNE SOCKET EES J ed 1 5 pus EXTENSION LS SOCKETS C27 C28 R23 TAGS ON SWITCHES 53 6 54 SHOWN THUS O ARE USED FOR ANCHORING PURPOSES ONLY ARE NOT CONTACTS 18 TC4 C26 TO TELEVISION AERIAL 35 6008 BAIRD SERVICE TELEVISION AERIAL AND LOUD SECTION 1 MANUAL SPEAKER CONNECTIONS 35 4020 T18 AND T20 AERIAL FEEDER CABLE PLUG CONNECTIONS BRAIDING TO CASE CENTRE CONDUCTOR amp SMALLER PIN TO LARGER PIN SOLDER YW 2222222 222222 35 6003 T18 AND T20 LOUDSPEAKER CIRCUIT DIAGRAM lo Sp o LLLI FLEXIBLE LEAD t 7 HUMBUCKING COIL 35 6004 SERVICE MANUAL RESISTORS K X by 1000 W Wattage M Megohm iw R 2 200K iw R 3 15K lw RA 15K iw R 5 50K iw R 6 100K iw R 7 2K 2
10. V 4 Pentode T 20 POWER PACK The power pack consists of two separate power supplies The main power for the receiver is supplied from one transformer and I W 4 350 rectifier valve V 5 and supplies 330 volts D C at 120 milliamps 4 volts at 20 amperes for heater supplies and 20 volt heater supply for valve in the time base The 300 ohm loudspeaker field is used for smoothing Additional smoothing required for the vision unit and synch selector valve is obtained from L 9 The 230 volt tap on the primary of the power transformer is used as an auto transformer to maintain a fixed input voltage input to the E H T transformer which gives 3 200 volts A C and 4 volt heater feed to HVR2 rectifier V 6 developing a D C potential of approximately 4 400 volts The On Off main switch is ganged to V R 1 sound volume control RESISTORS K X 1000 W Wattage M Megohm RJ iw R 2 150 ohms Iw RJ 50K iw 4 75K iw R 5 20K 2w R 6 50 ohms iw RJ 50 ohms iw RS 5M iw R 9 250 ohms iw R 10 100K iw Ril 10K iw 12 250K iw R 13 1M iw R14 50K iw R 15 300 ohms iw 16 500K iw R17 100K iw R18 5K Iw R 19 10K iw R 20 10K Iw 21 5K iw R 22 100K iw R 23 10K lw R 24 2M iw R 25 250K iw R 26 250 ohms iw R 27 80K lw R 28 400 ohms 3w R 29 50 ohms 4
11. cy Changer I F Amplifier Detector A V C Rectifier and Audio Amplifier Pentode Output Valve H T Rectifier 5 000v Rectifier COILS L 11 330 0 330 V A C Rectifier Secondary Winding L 12 20 A C Heater Winding L 13 4 20 amp A C Heater Winding for Sound Time Base and Vision L 14 C R T Heater Winding L 15 Mains Transformer Primary Audio Output Transformer Secondary L 16 E H T A C Secondary 3 200v Smoothing Choke H T Supply 4 v A C Rectifier Heater Winding 1 17 E H T 4 v Heater Winding L 18 E H T Mains Transformer Primary SECTION 15 2 35 4020 CIRCUIT DIAGRAM SERVICE 20 POWER PACK AND SOUND MANUAL BAIRD e 115 ES x NOISIA Q 8H 422 yu 1501 134205 15V8 3WIL ve IYA 5 CYA d3ONVO 25915 c5 9009 SE SISSVHD 2740 5138206 miyav This service manual 2014
12. d into the control grid top cap of valve V 2 Adjust carefully broadcast trimmers T C 13 and T C 14 for maximum output Coils L 22 L 23 Transfer generator output to the control grid of the frequency changer and trim T C 6 and T C 7 Coils L 17 L 18 After the alignment of the broadcast I F s switch back to Television and with generator at 2 5 megacycles re check the television I F alignment T C 12 and T C 15 R F ALIGNMENT LONG WAVEBAND Set the signal generator and the scale pointer to 1 300 metres 230 kilocycles Feed the generator into the aerial and earth sockets through a standard dummy aerial Adjust oscillator trimmer T C 10 and aerial trimmer T C 3 Coils L 16 L 6 Check calibration at 1 800 metres 167 kilocycles MEDIUM WAVEBAND With generator and scale pointer at 200 metres 1 500 kilocycles adjust oscillator trimmer T C 9 and aerial trimmer T C 2 Coils L 14 L 4 Check at 300 and 500 metres 1 000 and 600 kilocycles SHORT WAVEBAND Feed generator into aerial socket through a 400 ohm resistance With scale pointer set to 20 metres 15 megacycles adjust oscillator trimmer T C 8 Coil L 12 on the peak requiring the smaller trimmer capacity 2 oscillator frequency high Adjust aerial trimmer T C 1 Coil L 2 Check at 50 metres 6 megacycles TELEVISION The television R F alignment must be carried out feeding the generator into the aerial lead to the vision receiver and no
13. eiver as in the broadcast receiver but the circuit arrangement and intermediate frequency used are different Intermediate frequency on television band is 2 5 megacycles instead of 465 kilocycles the audio amplifier pentode valve V 4 is used also as a reflex radio frequency amplifier This arrangement alters the circuit specification adding an extra R F stage The television sound signal is fed from the aerial via R 1 Vision unit coupling coil L 7 and aerial coil L 8 to the grid of pentode valve V 4 amplified at R F and applied to the grid of the frequency changer valve V 1 which amplifies and converts the R F signal to the intermediate frequency of 2 5 megacycles The signal is amplified at 2 5 megacycles via LF coils L 21 L 24 and valve V 2 Detector A V C and audio amplifier circuit is the same as used on the broadcast bands A special switching arrangement permits the use of television sound only See Vision Unit summary LOUDSPEAKER A special Rola loudspeaker with 300 ohm field winding and suitable output transformer is used Section 13 1 T 21 RADIO GRAMOPHONE Section 10 4 shows special circuit modifications when T 18 chassis is used for T 21 Radio gramophone Signal voltages from the pick up are applied to V4 Grid via R 32 R33 and 1 Potentio meter circuit R 32 R 33 reduces the signal voltage to avoid overloading of V 4 1 and 5 7 control is removed from the chassis to the front of the cabinet and Radio G
14. er and not with the generator connected into the sound receiver signal generator with an accurate and stable frequency calibration at 41 5 megacycles and an output impedance of 75 ohms must be used Should there be any doubt about the generator accuracy it is advised that the B B C Tuning Signal be used for R F alignment preferably from an aerial giving a weak signal non metallic trimmer screwdriver must be used Set the tuning control T C 5 approximately at half capacity and adjust T C 2 Coil L 4 L 5 for maximum output on the peak requiring the larger trimmer capacity oscillator frequency low It may be found that there is only one peak position if so this is the correct one Adjust R F aerial coil trimmer T C 1 for maximum output BAIRD SERVICE T 18 T 20 AND 21 SECTION II 5 MANUAL CIRCUIT SUMMARY 35 4020 AERIAL FEED The aerial feeder cable which must be terminated in the non reversible two pin plug Section 13 1 is plugged into aerial socket Section 10 2 and the sound aerial plug from the vision unit is taken to the sound aerial socket on the power pack and sound unit Section 10 1 and 8 VISION UNIT The unit comprises two tuned radio frequency band pass coupled stages with three megacycle band pass diode detector and video amplifier incorporating three Mullard TSE4 secondary emission valves and Mazda D1 special low capacity diode rectifier VISION SIGNAL The radio frequency signal from the te
15. iw 12 50 P F R 10 1M lw 13 0001 mfd T C 14 01 mfd T Bells Coe ORBI 15 001 mfd R12 50K iw 16 02 mfd T R 13 20K C 17 01 mfd T 14 500 lw 18 01 mtd T R 15 100K lw C 19 2 mfd 300 v w E 1 20 50 mid 2 v w H 21 50 mfd E 12 v w R17 10K 22 35 mfd R 18 80K lw 23 16 mfd E 450 v w R 19 250 ohms iw C 24 16 mfd E 450 v w R 20 50 ohms 4w R 21 07 ohms 20 s w g Eureka R 22 50K iw R23 2M lw VARIABLE RESISTORS 1 500 Audio Volume Control V R 2 100 Tone Control 8 5 Vision Contrast Control V R 4 10 Tube Brightness con L 1 1 2 L 3 L 4 L 5 1 6 LJ L 8 L 10 trol V 1 Mazda V 2 VP4 B Mullard 3 TDD4 Mullard 4 PEN A 4 Mullard V 5 W4 350 Mullard V 6 H V R 2 Mullard Aerial Coupling Coil R F Grid Coil 1st I F Coil 2 5 m cs R F Osc Transf Secondary R F Osc Primary 2nd I F Coil 2 5 m cs Audio Output Transtormer Primary C 25 16 mfd E 450 v w C 26 8 m d E 120 v w C 27 02 mfd 5000 v w C 28 0 1 mfd 400 v w T C 29 0 1 mfd 400 v w T VARIABLE CONDENSERS T C 1 30 P F R F Grid Coil Trimmer T C 2 30 P F Osc Tuning Preset T C 3 20 P F Trimmer T C 4 20 j T C 5 25 P F Osc Tuning Sound T C 6 30 P F I F Trimmer VALVES Frequen
16. levision aerial is fed via sound rejector circuit L 1 V C 1 to the grid circuit L 2 V C 2 of the first R F valve V 1 amplified and applied to the second R F amplifier valve V 2 via band pass coils L 3 and 10 L 8 coupling coil The amplified output of V 2 is applied via similar band pass coils L 11 L 13 L 12 coupling coil into low capacity diode rectifier and the video frequencies developed across the diode load resistance R 19 are applied to the grid of V 4 via L 14 Amplification at video frequency is given by V 4 Positive picture modulation voltages are developed at the anode of V 4 which is capacity coupled to the modulator electrode of the Cathovisor tube by the flying lead from end tag on the sub assembly panel The auxiliary cathode of V 4 gives output volts in the opposite sense for the time base synchronising selector circuit Picture contrast and R F sensitivity of the vision unit is controlled by V R 3 Sections 12 3 15 2 Switches 5 5 and 5 6 which are ganged to V R 3 switch Cathovisor Tube heater supply and the mains to E H T transformer 5 5 5 6 operate to OFF when V R 3 is turned anti clockwise low contrast allowing television sound only to be used with economy TIME BASE UNIT AC2 HL Triode synch separator valve 41 or AC P Triode frame scan generator valve 41 MP Triode line scan generator valve U R 1 C Diode line scan generator valve 2D4A Diode frame synch coupling val
17. ound receiver is integral with the power pack chassis T 18 BROADCAST BAND SPECIFICATION 1 TH4A TH4B Triode hexode frequency changer V 2 VP4B Pentode amplifier V 3 2D4A Double diode second detector and A V C rectifier V 4 5 Pentode audio amplifier V 5 PEN B4 Pentode output valve Radio frequency input from the aerial is coupled to triode hexode frequency changer valve V 1 with aerial coils L 1 to L 6 and R F signals amplified and converted to 465 kilocycles intermediate frequency V 2 valve amplifies the signal at and double diode valve V 3 rectifies the LF signal giving rectified volts for A V C and for amplification at audio frequency Two stages of audio frequency amplification are employed pentode amplifier V 4 and pentode output valve V 5 A V C is fed to both V 1 and V 2 on medium and long wavebands to V 2 only on short and television wavebands Volume is controlled by V R 1 audio frequency voltages developed across diode load resistors R 12 R 13 are fed via V R 1 to grid of V 4 Tone control V R 2 C 23 is connected between V 5 grid coupling condenser C 22 and earth T 18 TELEVISION SOUND WAVEBAND SPECIFICATION V 4 Reflex R F Pentode amplifier V l Triode hexode frequency changer 2 Pentode intermediate frequency amplifier V 3 Double diode detector and A V C rectifier 4 Pentode audio amplifier V 5 Pentode output valve The same valves are employed for the television sound rec
18. ovisor Cathode Ray Tube has been greatly simplified The internal assembly consists of the following electrodes 1 Heater and cathode combined 2 Modulator For cap connections see Section 10 4 3 Anode The heater is A C fed and the current regulated to 2 5 amperes The anode is at 4 800v potential on Type 12 M W 2 Tubes 4 400v potential Type 9 M W 2 The high voltage connection to the anode is made on the side of the glass envelope Picture modulation from V 4 anode vision unit is applied to the modulator electrode via C 25 and controls the electron beam thereby varying the picture contrast according to the video frequency voltages developed by the vision unit Brightness is controlled by a variable positive cathode bias voltage obtained from a variable potentiometer across the main H T supply V R 4 Sections 12 3 15 2 The modulator electrode is connected to earth via R 18 Vision unit FOCUS Focus of the electron beam is effected electro magnetically Anode current taken by valves V 3 V 6 through focus coil L 10 produces an approximately correct magnetic focussing field L 10 being located round the neck of the Cathovisor tube Accurate adjustment of focus is made by V R 3 Focus Control a limited variable resistance between L 10 and earth T 18 T 20 AND 21 CIRCUIT SUMMARY SECTION II 7 35 4020 BAIRD Manua T 18 and T 21 POWER PACK AND SOUND UNIT The four wave band superheterodyne s
19. ramophone Switch S 8 fitted in its place A special loudspeaker is used in the T 21 receiver and C 37 smoothing condenser is removed from the field winding POWER PACK The power pack contains two separate power supplies The main power for the receiver is supplied from one transformer and LW 4 350 rectifier valve V 7 and supplies 330 volts D C at 120 milliamps 4 volts at 20 amperes for heater supplies and 20 volt heater supply for U R 1 C valve in the time base T 18 T 20 AND 21 CIRCUIT SUMMARY SECTION 8 35 4020 BAIRD Manua The 300 ohm loudspeaker field is used for smoothing additional smoothing required for the vision unit and synch selector valve is obtained from 1 37 The 230 volt tap on the primary of the power transformer is used as an auto transformer to maintain a fixed voltage input to the transformer which gives 3 200 volts A C and 4 volt heater feed to an HVR2 half wave rectifier V 6 which develops a D C potential of approximately 4 500 volts This potential is connected in series with the main 330 volt D C power supply making a total effective voltage to the 12 M W 2 Cathovisor tube anode of 4 800 volts The On Off mains switch is ganged to V R 1 sound volume control T 20 POWER PACK AND SOUND UNIT SOUND SPECIFICATION Four valve 7 23 metre superheterodyne receiver 1 AC TH1 Triode hexode frequency changer V 2 VP4B Pentode amplifier V 3 TDD4
20. re must now be re centred as described if this adjustment is made SYNCHRONISING When setting lock controls do so with low picture contrast as this is the worst receiving condition and synchs will hold over the minimum to maximum contrast range Frame Lock should be set so that the picture locks when running upward Line Lock should be set in a hard lock position which may be recognised by the whole picture moving from right to left when coming into the correct lock position SERVICE 18 AND 21 SOUND RECEIVER SECTION 3 BAIR MANUAL ALIGNMENT PROCEDURE 35 4020 Turn vision contrast control V R 1 to left thereby switching off the E H T volts to avoid possibility of high voltage shocks Set volume control V R 1 to maximum Set tone control V R 2 to low anti clock from front Connect A C output meter with condenser in series between the anode of the output valve 5 and chassis The meter should be capable of giving a reasonable deflection at about 20 volts ALIGNMENT Set the wavechange switch to television with the scale pointer on Television Set the modulated signal generator to 2 5 megacycles and connect to the control grid top cap of the frequency changer valve V 1 Adjust the television I F trimmers T C 12 and T C 15 for maximum output Coils L 21 L 24 Set the wavechange switch to medium waves and pointer to approximately 300 metres Set the signal generator to 465 kilocycles and fee
21. rect position for the coils is when they are equally spaced in relation to each other It is important that the line is correctly adjusted horizontally or picture will appear twisted Reassemble the Line Coil Screen and Flux Links taking care not to disturb the position of the coils FRAME SCAN ADJUSTMENTS The Frame deflection is in the vertical direction and it is not necessary to make individual focus adjustment in this plane all the adjustments being concerned with the vertical shape of the picture If the verticals are twisted in one direction that is both sides of picture parallel but not vertical the Frame Yoke fixing nuts should be loosened and the whole yoke twisted in the required direction The Flux Link clamping screws should be slackened first in order that the line deflector coils will not be disturbed Should the limit of the yoke traverse be reached before the necessary vertical correction is obtained secure yoke in its optimum position and make further adjustment by rotation of the line coil screen only not line deflector coils which must be left in their correct BAIR SERVICE C R TUBE AND TIME BASE SECTION 2 MANUAL ADJUSTMENTS T 18 T 20 21 35 4020 horizontal position These adjustments can best be made by removing modulation and reducing line amplitude by altering Line Lock control until both sides of the screen are visible inside the mask Should trapezoidal distortion be present 7 e the picture wider at the
22. t with the generator connected directly into the sound receiver A generator with an accurate frequency calibration at 41 5 megacycles and an output impedance of 75 ohms is essential A non metallic trimmer screwdriver must be used If there be any doubt about the accuracy of the generator it is better to use the tuning signal of an actual transmission preferably from a weak aerial Set the pointer in the middle of the word Television Adjust oscillator trimmer T C 1 Coil L 20 on the peak requiring the larger trimmer capacity t e oscillator frequency low Adjust R F trimmer T C 5 Coil L 10 and aerial trimmer T C 4 Coil L 8 for maximum output BAIRD SERVICE T 20 SOUND RECEIVER SECTION 11 4 MANUAL ALIGNMENT PROCEDURE 35 4020 Turn vision contrast control V R 3 to left thereby switching off the E H T volts and avoiding possibility of shocks Set volume control V R 1 to maximum Set tone control V R 2 to low Connect output meter with condenser in series between V 4 anode and chassis meter giving a reasonable deflection at about 20 volts should be used I F ALIGNMENT Set the modulated signal generator to 2 5 megacycles and feed into the control grid of V 1 Adjust the I F trimmer T C 3 Coil L 3 for maximum output Adjust the I F trimmer T C 6 Coil L 6 for maximum output R F ALIGNMENT The R F alignment must be carried out feeding the signal generator into the aerial lead to the vision receiv
23. to obtain focus current in the focus coil Carefully turn Brightness up until spot is visible adjust focus coil adjusting nuts until spot is in centre of screen Rotate focus coil round the tube until spot is circular in shape when set to be approximately in diameter The spot should remain circular when focus control is turned and causes the spot to reduce in size through a minimum and then up again to diameter It will be found that there are two positions of the focus control where it is possible to obtain a spot 1 diameter and it is to each of these positions that these adjustments refer Take great care to keep the Brightness low to avoid burning the screen Coil rotation is limited by the connecting wire but approximately 180 movement is possible in both clock and anti clock directions LINE SCAN FOCUS AND HORIZONTAL PICTURE ADJUSTMENTS Remove 7K resistor and replace line scan generator valve V 3 Adjust focus control until a thin fine horizontal line is traced across the screen If the focus control will not give sufficient adjust ment vary the line lock control until correct focus is obtained If the line is not of even width all over its trace remove the Line Coil Screen and Flux Link Clamps readjust Focus and Line Lock controls as previously explained until line is correctly focussed in the centre and adjust the line deflector coils in relation to each other until the line is of equal width overall and horizontal The cor
24. top than at the bottom or vice versa the two pairs of arms on the top of the frame yoke should be adjusted until the distortion is removed Finally adjust Frame Amplitude control until picture height is in correct ratio to picture width PICTURE CENTRING The picture should always be centred in the mask under transmission picture conditions That is during a transmission in which the blackouts are in their correct ratio It is not advisable to centre a picture on the cross test bar as the blackouts are too wide and differ from the normal transmission Picture centring is accomplished by rotating the three Focus Coil Adjusting Nuts individually until picture is central in the mask FOCUS The focus control should always be the final time base adjustment and if it is not possible to obtain focus by rotation of control first ensure that the correct mains tap is connected and then check whether the focus control is at its maximum or minimum resistance Maximum resistance Rotated clockwise from the back Minimum resistance Rotated anti clockwise from the back If control is at maximum resistance move the focus coil towards the back of the set If at minimum resistance move coil towards the screen The focus coil needs more current to focus the electron beam when near the anode or gun and less current when nearer to the screen Focus control is a Variable resistance which takes more current through the coil when resistance is lowest Pictu
25. ve 2D4A Diode line synch coupling valve SYNCHRONISING PULSE SELECTION The voltages at the auxiliary cathode of V 4 valve vision unit are capacity coupled to the grid of the pulse selector valve V 1 time base which removes all modulation other than 50 and 10 125 cycle frame and line speed synchronising pulses The selected pulses synchronise the scan generator valves V 3 and V 6 as later described LINE SYNCHRONISING The 10 125 cycle pulses are fed from the anode of V 1 time base via condenser C 3 to cathode of diode valve V 2 which valve injects the line speed synch pulses on to the grid of the line scan generator valve V 3 LINE SCAN GENERATOR CIRCUIT Electromagnetic principle is employed for line deflection V 3 valve with scan transformer coils L 1 and L 2 form an oscillatory circuit which develops a linear saw toothed current waveform in the line deflector coils L 3 and L 4 which are connected BAIRD SERVICE T 18 T 20 AND 21 SECTION II 6 MANUAL CIRCUIT SUMMARY 35 4020 across L 2 and arranged round the neck of the Cathovisor tube The current flowing through these coils forms an electromagnetic field which deflects the electron beam in Cathovisor tube horizontally at the line frequency of 10 125 c p s 405 lines per frame The speed of the generator is controlled by V R 1 line lock and limited by the value of R 7 The diode valve V 4 is connected to V 3 generator valve anode to cathode
26. w 5K iw R5 5K iw R 6 1250 ohms iw R 7 150K iw 20K Iw 35K lw R 10 70K dw 5K dw 12 5K iw R 13 7 5K dW 14 5K iw R 15 1250 ohms iw R 16 150K dw 17 20K Iw R 18 500K iw R 19 10K iw R 20 5K iw R 21 200o0hms iw R 22 5K iw R 23 70K iw R 24 20K w w tapped at 15K 35 paralleled CONDENSERS C 1 30 P F C 2 100 P F 002 mtd 4 002 mfd 5 002 mtd C 6 002 mfd C 7 002 mfd C 8 002 002 mtd C 9 002 mfd C 10 0 1 mfd C 11 002 mfd 12 4 mfd E C 13 002 mtd C 14 002 mtd C 15 002 mtd C 16 002 mtd C 17 002 mfd 18 002 mfd 19 002 mfd C 20 002 mfd 21 002 mfd 22 002 mfd 28 002 mfd C 24 15 P F C 25 02 mtd C 26 02 mfd C 27 002 mtd C 28 002 mtd C 29 200 mtd E C 30 4 mfd E COILS L 1 L 2 L 3 L 4 1 5 1 6 LJ L 8 L 9 L 10 L 11 L 12 L 13 L 14 L 15 L 16 L 17 L 18 Sound R F Rejector Coil Capacity tuned Vision R F Grid Coil Capacity tuned Vision R F Band Pass Anode Coil Inductance tuned R F Choke H T Supply Ist valve R F Choke V 1 Screen R F Choke Heater supply n Choke Heater supply Band Pass 2 coup ling coil R F Choke V 2 Screen R F Band Pass V 2 Grid
27. w R 30 07 Eureka Wire R 31 300 ohms lw BAIR MANUAL CONDENSERS oOO0o000000000000000o0oooooooooondg fo 90 1 82 Qi Qo Bo Mm Qo Tubular Electrolytic 0008 mfd 0 5 mfd 05 mfd 05 mfd 100 100 P F 556 P F 316 P F 100 P F 180 P F 180 P F 180 P F 180 P F 0 1 mfd T 05 mfd T 05 mfd T 05 mfd 0001 mfd T 0001 mfd T 0001 mfd T 02 mfd T 02 mfd T 02 mtd T 001 mfd 50 25 P F 0 25 mfd T 02 mfd T 50 mfd E 50 mfd E 2 mfd E 16 mfd E 16 mfd E 16 mfd E 0 25 mfd 0 1 0 35 mfd 8 E 02 mtd 001 mfd 05 mfd VARIABLE CONDENSERS d 0005 mtd V C 2 0005 mfd Ganged Tuning Condenser SERVICE 18 SOUND AND POWER PACK SECTION 12 7 COMPONENT VALUES B D 35 4020 VARIABLE RESISTORS 500 K Pot Audio Volume Control Ganged to S 7 V R 2 100 K Pot Audio Tone Control V R 3 5K Vision Contrast Con trol V R 4 10 Pot Brightness Control V R 5 0 9ohm Tapped C R Tube Heater resistance SWITCHES 1 5 2 4 way Yaxley ganged 5 3 wave change switches 5 4 5 Heater switch ganged to V R 3 Vision 5 6 E H T Mains transformer ganged to V R 3 Vision 5 7 Main On Off Switch ganged to LOUDSPEAKER Rola Type F 6 D C resistance of field 300 ohms D C resistance of O P Transf
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