Ampeg SVT-6 Pro No Output

[ca7922303]

What I think is that you have the transistor legs mixed up. Otherwise, your readings make no sense at all.

[ca7922303]

Just removed one leg of all 60 resistors on Ch 1(-) board. Found one(1) bad N channel 240 mosfet. Believe that could be reason Ch 1(-) voltages are wrong. All 60 resistors read good out of circuit. Have to order mosfet.

[ca7922303]

Is Q18 a 2n3440?
nosaj
https://my.centralsemi.com/datasheets/2N3439.PDF

So I've removed Q18 again and here's what I'm getting: Red to Base/Black-Collector(0.6)
Base-Emitter(0.6v) Collector-Emitter(OL)

Black to Base/Red-Collector(OL)
Base-Emitter(OL) Collector-Emitter(OL)

[ca7922303]

Removed one leg on all 60 resistors associated with mosfets on Ch 1(+) board due to load on variac@75vac. Ch 1(-) board was completely unplugged. Checked all mosfets and they all read good and all turn on/off. Now looking for what's causing load on variac Ch 1(+) board only.

[ca7922303]

Is Q18 a 2n3440?
nosaj
https://my.centralsemi.com/datasheets/2N3439.PDF

Do the revised Q18 numbers look right?

[g1]

Yes, that's better.

[ca7922303]

Yes, that's better.

Thanks for that. Still searching for why the voltage difference between (+)/(-) boards. Found some loose lugs(j47/48), resoldered them, but still getting voltage difference. The mosfet I thought was bad, is actually good, double/triple checked it again with new batteries in DMM and all 20 mosfets read the same/good.. Anyway to get some theory on the complete Ch 1(-) circuit so I can follow the schematic(which is not getting me there). Thanks.

[ca7922303]

Now have about (+2/-2 vdc) with variac@20vac on gate busses Ch1+/Ch 1(-). R53(OL). It was checked recently and was good, but maybe all the new transistors and two(2) IC's caused it to blow.

[ca7922303]

Gate busses @ (3.4vdc) with variac@120vac.. AP1/2 both @ about 1:00. Can hear/feel both relays clicking @ around (90vac on variac). Signal generator @1000 hz/0.30v sine plugged into power amp in. Not getting a signal out to speakers. Measuring across source resistors(11mvdc).

[ca7922303]

All test point voltages about 20% higher than schematic shows, but everything seems good up to relays.

[ca7922303]

Finally got it going and only 327 posts(most of them at the end, my own). Mosfet solder connection fixed it. Thanks to all that helped. Nevetslab and especially G1. He is definitely the Great One.