Fender Twin Amp 1994, Service Manual

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’94 TWIN AMP
THEORY OF OPERATION(CONT)
switch from +454Vdc to +230Vdc. This voltage change only affects the four output tubes. The high voltage supplies for the
preamp tubes are tapped off prior to the output switch (S9). When switching the high voltages at the power tubes, the negative
Bias voltage must also be switched. The Bias supply is derived through a voltage doubler from the Brown secondary of the
power transformer. S9B determines the path of the Bias current. The low power path is through R97 (100K), and the high power
path is through R98 (18K) and R97 (100K) in parallel. R96 (82K) sets up the voltage divider that feeds the Bias and Balance
controls (-52Vdc High, -21 Vdc Low).
Note: It is recommended that the amplifier be in the Stand-by mode before switching the High/Low Output switch.
LOW POWER OPTION
The ’94 Twin Amp can be run with only two output tubes instead of four. This is done by removing the inner two 5881/6l6wgc
tubes. The Impedance Selector switch must be set to one-half the total speaker load. The rule is ---half the tubes---half the
impedance. Therefore when using the internal two speakers (16
Ω
load), the Impedance Selector switch must be set to 8
Ω
. This
will produce 60 watts RMS in the Output High setting, and 15 watts RMS in the Output Low setting.
PARTS LIST
NOTE: SHADED ITEMS ARE FOR REFERENCE ONLY
PRINTED CIRCUIT BOARD ASSEMBLY
QTY PART # DESCRIPTION REFERENCE DESIGNATION
1 048973 CABLE RIBBON 9 CKT 15 ¾ IN P3A
1 048972 CABLE RIBBON 9 CKT 9 ¾ IN P2A
1 038691 CAP AE AX 4.7 UF 50V C35
7 009512 CAP AE AX 22 UF 25V 20% C1,5,11,24,28,53,61
4 024819 CAP AE AX 22UF 500V C22,42,43,44
4 036954 CAP AE RDL 22UF 63V 20% C36,37,59,62
4 024820 CAP AE AX 47UF 350V C40,41,51,52
1 028471 CAP AE RDL 47UF 50V 20% C60
2 031040 CAP AE RDL 100UF 100V 20% C45,50
2 013638 CAP AE AX 220UF 285V C38,39
2 028482 CAP AE RDL 220UF 50V 20% C46, 49
2 039362 CAP AE RDL 1000UF 35V LOPROFIL C47,48
1 025982 CAP CD 68PF 1000V 10% C4
2 020917 CAPCD 250 PF 1000V 10% C6, 17
1 025777 CAP CD 470PF 1000V 10% C25
2 011435 CAP CD 680PF 1000V 10% C13,27
1 017620 CAP CD 1500PF 1000V 10% C31
1 039265 CAP CA 2200PF 100V C30
2 026202 CAP PFF .0022UF 600V C10,14
3 025962 CAP PFF .0047UF 400V C12,29,65
2 027275 CAP MPF .068 UF 100V C57,58
7 024833 CAP MPF RDL .022UF 400V 10% C3,8,9,16,18,26,63
2 024835 CAP MPF RDL .022UF 630V 10% C32,33
2 024853 CAP MPF RDL .1UF 250V 10% C23,34
5 024854 CAP MPF RDL .1UF 400V 10% C2,7,15,19,21
2 027281 CAP MPF .22UF 63V C55,56
1 027286 CAP MPF .47UF 63V C54
1 024876 CAP MPF RDL .68UF 250V 10% C20
1 049028 CONTROL POT 1M 2B W/DPDT R39 (CHANNEL 2 VOLUME)
1 047781 CONTROL SNAPIN 1K 15C R82 (PRESENCE)
2 041510 CONTROL SNAPIN 25K B R19, 37 (CHANNELS 1&2 MID)
1 037600 CONTROL SNAPIN 100K B R62 (REVERB)
4 037597 CONTROL SNAPIN 250K 30A R17,18,35,36 (CHANNELS 1&2
TREBLE,BASS)
1 047780 CONTROL SNAPIN 250 K 30A R23 (CHANNEL 1 DRIVE VOLUME)