Velocette 12-R
Contents
1. S _ CONNECTORS 1 o E S e _ 72 HEAD 3W 2 HTRO HTR1 HTR2 CRIMP CONNECTORS 72 CRIMP PCB TAB TX1 14 LS1 x2 SOCKETS a ee _ 1 4 MONO JACK SKT 72 SKT JCKBNBG SK1 SK2 SK3 SK4 OU NO SWITCHES ON ____ _ _ _ 2 h Large slide DPDT horiz 73 SWT SLIDER DP Mini Toggle SPDT vert 73 SWT M TGL PCB re S POTENTIOMETERS a ee es Co VALVE BASES 1 41 7 B9A valve base 73 VAL SOCKET Vi V2 V3 V4 ee FUSE HOLDERS 72 FUS HLD PCB 2 FS1 FS2 FS3 FS4 040000000021 TEST 73 PIN TERM 1 _2______ 0220 HEAT SINK _ 71 HS PF752 Co FLYING LEADSETC ee o a o Cathode heater lead C00 LEAD VEL12 insert into HTRO HTR1 amp HTR2 HTR Reverb input lead C00 FLY TRAMP R REVERB IN Reverb output lead C00 FLY V12R REVERB OUT Grommet 45 GROMM 2 put over reverb leads before into PCB VELOCETTE 12R CIRCUIT DISCRIPTION Please refer to circuit diagram for DC voltages and other information INPUT SECTION AND PREAMP SK1 and 5 are the LO and HI sensitivity inputs respectively When the LO socket is used R5 R39 and R3 act as a potential divider to reduce the input level to the preamp C3 has two purposes firstly to block any DC from the input that m2. a twisted pair connecting lead to V3 and V4 after first going through the secondary fuses 25 2V DC supply is highly regulated supply using BD647 TR7 as the main regulating device Please ensure that the small clip on heat sink is attached TR7 TR1 TR2 provide a constant current source for 43 the 15 volt zener The output voltage is set by the ratio of R59 and R67 which provide the feedback to TR7 via 9 TR10 to stabilise the whole circuit and TR11 with R80 and R81 form a current limiter This allows the supply voltage to ramp up at switch on when the heater filaments of the preamp valves draw considerably more current while cold R27 and R57 halve the supply voltage to provide the opamp bias voltage and as shown on the circuit diagram the DC supply is routed first through the two filaments in V2 in series and then through the two filaments in V1 This will result in each filament having the nominal 6 3 volts across them Paul Stevens 2 January 1997
3. the actual gain being dependant on the impedance ftrequency curve of the reverb tray Because of this it is crucial to the correct operation of the reverb that the right reverb tray is used This should be an Accutronics 8CA3B1B The output of the reverb tray goes into IC2B This is configured as a differential amplifier as a way of reducing any hum that may be picked up on the sensitive reverb return leads RV3 controls the level of the reverb Across pins 1 2 is TR6 a J175 FET When 5 4 is shorted out by a footswitch TR6 is also effectively shorted which results the reverb being turned off The reverb signal is then mixed with the dry signal R58 before going into the phase splitter POWER STAGE The phase splitter V2A and V2B is a differential input splitter which produces the two anti phase signals necessary to drive the push pull output stage V3 and V4 are the two EL84 output valves connected as a push pull cathode biased class A power amplifier The quiescent current is set by R24 which is bypassed by C19 for extra gain SW1A and SW1B 15 an electrically robust slider switch used to switch the power valves from Pentode to Triode operation For Pentode operation the screen grid grid 2 9 Is connected via the screen grid current limiting resistors R25 and R26 to the highly smoothed screen grid supply G2 positive pin of C23 For Triode operation the screen grid of each valve is connected to the co
4. PO EXCEPT WHERE SHOWN COMPONENTS USED ARE AN APPROVED TYPE NUST BE REPLACED ACCORDINGLY ISSUE ISSUE ISSUE CHANGE NOTE CHANGE NOTE CHANGE NOTE DATE DATE DATE RSUE ISSUE ISSVE CHANCE NOTE CHANGE NOTE CHANGE NOTE DATE DATE DATE REVERS 417 REVERB 642 100 1 ACCUTRONCS REVERB F S SKT OV OV 2524 70077 5 cs 000 2 TITLE REVERB GPAMP SUPPLIES AND FOOTSWITCH TRACE ELLIOT LTD 1 NALDON ESSEX CNS 480 19 MARCH 1999 SREAT PAUL STEVENS 2102 855288 01521 851975 C32 PCB PC00064x3 VELOCETTE 12R ISSUE 3 14 2 97 PS mere ees 4 14 RESISTORS a 1 1 0 14 7 72 6 R3 R4 R9 R17 R18 R44 R25 R26 Co S SEMICONDUCTORS 233904 72 2 3904 TRO 10 11 4415 72 175 1 16 es CAPACITORS 2 ee 470p ceramic 72 C470P 1KVCD_ 1 6 100p 100 axial 72 100 100 1 3 100n 100V axial 72 C100N 100VCA 2 18 21 27 28 36 50 60 61 a 471 400V poly box 72 C47N 400VP_ 1 4 2 2 ee 1007 16 electrad 72 C100 16VER 4 51 C52 053 C62 1004 400V electrad 72 CAP 100400v_ 2 022 C23 4700 35 72 4703 1 C48 a
5. TRACE ELLIOT SERVICE MANUAL NO SM00025 Date Product Code Model Technical File No ISSUE 1 January 6 1997 13455 3456 Velocette 12R Alnico 00025 Issued by Trace Elliot Limited Blackwater Trading Estate The Causeway Maldon Essex CM4 4GG ISSUE ISSUE ISSUE CHANGE NOTE CHANGE NOTE CHANGE NOTE DATE DATE DATE RSUE ISSUE ISSVE CHANCE NOTE CHANGE NOTE CHANGE NOTE DATE DATE DATE HTZ GIBSON GOLD TONE GUITAR AMPLIFIER HT1 GA 15RV CT JJ V 16 OHM EXT lt la a 5 2 Tho La INPUT 200 Gl REVERB_IN 2 4 1 B 220 ADD CORRECT 2 LINK SKi x VALUE OF es ENS INT SPEAKER 6 100n HI INPUT cu 4 SK3 Sl 2 47 2 NPUT DECOUPLING TO CHASSIS VOLUME amp BRIGHT TONE A 100 REVERB_OUT GNOI OV TPS TPA TP7 30 344V 5557 20 R32 R30 R31 c30 KS TX2 FS m 2453 417 9 O Fane 5 7x1 C3 A 5 LJ rA n7 alg 1 HEATER WIRING ON TWISTED PAIR CABLE C27 ale 100On 4 9 on 100 V TPO DV OV CNOS 04 VALVE SECTIDNS SUPPLIES amp BIASING GIBSON GOLD TONE 15 TRACE ELLIOT LTD 5200002 NALDYN ESSEX CNS 440 N 851851 851975 19 MARCH 999 PAUL STEVENS ALL VOLTAGES ARE SHOWN ARE QUESCENT SWITCH SET ALL VOLTAGES ARE DC AND REFERENCED TO T
6. ay unintentionally be present this would otherwise change the bias point of the first valve stage secondly the value of the capacitor has been chosen so that there is a slight roll off of lower frequencies this prevents the sound from getting too muddy Via is the first gain stage and is configured as a cathode bias common cathode voltage amplifier with bypassed cathode resistor for increased gain R6 and give a slight presence lift and the frequency of the Bright effect is set by C7 which when switched in is across pins 2 and 3 of RV1 Volume Obviously connected like this the amount of brightness added will decrease as RV1 is turned up Vib is the second gain stage configured similar to before C9 is added across the anode resistor R8 to smooth out the top end The Tone network is passive and controlled by RV2 This is a dual ganged potentiometer one part of which effectively controls the mids RV2B while the other part inversely controls the treble RV2A R28 R34 and R35 act as a potential divider to lower the signal sent to the reverb circuitry REVERB SECTION The signal from the preamp is fed into IC1A which is configured as a boot strapped voltage follower Z1 and Z2 have been added to prevent any nasty spikes from damaging the opamp this should in practise never happen C4 and R44 roll off a lot of the lower frequencies before the signal gets sent to and 2 These opamps are configured for current gain
7. rresponding anode Triode operation basically reduces the power output to a bit less than half and also reduces the high frequencies in the overall sound D5 and D10 have been added to give protection to the output transformer should a fault arise OUTPUT TRANSFORMER AND SPEAKER CONNECTIONS The output transformer has secondary taps for 160 8Q and 5 3 16Q tap is used to drive the External Speaker Output SK2 When a jack plug is inserted into SK2 the internal speaker is disconnected The three LINK positions are provided on the PCB so that different impedance internal Speakers be used in production Depending on whether the internal speaker is 160 80 or 5 3 the correct LINK should be fitted This has been done purely so that different impedance speakers can be used if there are any problems with supply POWER SUPPLIES All three supplies HT ac heater and DC supplies have secondary fusing on the PCB This is to protect the mains transformer and for approvals The HT supply is a very simple bridge rectifier diode network with 4 7 1KV capacitors across each diode for EMC reasons which is then smoothed by C22 to supply the centre tap of the output transformer This is then further smoothed by R82 C23 R380 C25 and R31 C26 to supply the screen grids phase splitter and preamp respectively R29 is added to discharge the high voltage capacitors when then unit is turned off The ac heater supply is simply connected via
Download Pdf Manuals
Related Search