GIBSON GA30 GUITAR AMPLIFIER SCHEMATIC
This is one of the GA30 amps - there were a few by the sounds of it.
6SJ7 MIC PRE
Grid leak 1m
Grid stopper (none)
Ra 470k
Rk 2k2 20u bypass
Screen 2m2, 50n bypass
10n coupling cap to 500k volume pot. 100k mixing resistor to PI
6SJ7 INST PRE
Grid leak 470k
Grid stopper 47k (forms a voltage divider with the grid leak)
Ra 220k
Rk 2k2 (not bypassed)
Screen 2m2, 50n bypass
20n coupling cap to 500k volume pot. 100k mixing resistor to PI
470k NFB from OT secondaries, 700pf in series with bypass switch
6SN7 PHASE INVERTER
Ra 100k on each plate
Rk 1k shared (not bypassed)
50n coupling to 6V6
220k / 4k7 pair to PI grid
Tone 2m pot, mixing 250pf and 50n to grid of PI input
6V6
220k grid leak
Rk 250 ohms
No grid stoppers or screen resistors
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