Ampeg G-110

[cashin]

Hi, I have an Ampeg G-110, G110, G 110. Here is a schematic: Ampeg G110.pdf

The problem seemed like a burnt out / crackly volume pot that put out about half power (total resistance 50K ohms, rather than 100K.) I exchanged it and this didn't fix the problem. Seemed as if wiring the new pot into the circuit dropped the pot's total resistance. So I dove into some troubleshooting.

1) I found the juncture of IC1 pin 6 / Base of Q2 (the semiconductor / transistor labelled "Reverb Amp") reads 24 volts, rather than 13.5.
2) The Emitter of Q3 (labelled Preamp) reads 0 volts, rather than 13.
3) Q4, labelled FET on the schematic, was passing quite a bit of current in an unintended manner. I tested each transistor after removing it from the board like this: (link).

4) I think Q7 is functioning properly, despite initial concerns that the collector pin was broken off the TO-126 package.

Q7a.jpg Q7b.jpg

Seems that the transistor package & the heat sink to which it's mounted serve as the collector: I do get continuity between the broken collector nub and the heat sink and I rightly measure 24 volts between a heat sink and ground.

I'm asking for diagnoses, next steps, and where can I find replacement parts? I'm quite certain I'll need a new Q4- "610291-1." Google gives me nothing, and there are no additional markings on the transistor itself.

Thanks, Cashin