Acoustic 125 very low output.

[antieatingactivist]

That's what I said .

That you did. oops. Whats more likely, both drivers failing, but not completely dead? or something in the circuit?

[J M Fahey]

G one is on the right path.

Laundry list you should follow in due order:

1) power OFF, measure all diodes and transistors in circuit to catch shorts.
If any suspect, pull it to measure outside.

2) replace whateverīs needed.
Including smoked resistors and such.

3) build a lamp bulb limiter, get a 40 to 75W bulb.

Power ON
4) plug amp into it and measure voltages indicated in schematic.
You wonīt get full +78V because of loss in bulb, but I expect around +50V there, +/- 10V.
Other voltages will be proportional.
Say, if you have +V=50V, then "10V" point will be around 7V and so on.

Post results.

Letīs normalize DC before messing with Audio.

That amp, if working properly, gives a very usable 100W into 4 ohms, around what any Bandit or similar amp delivers.

[antieatingactivist]

G one is on the right path.

Laundry list you should follow in due order:

1) power OFF, measure all diodes and transistors in circuit to catch shorts.
If any suspect, pull it to measure outside.

2) replace whateverīs needed.
Including smoked resistors and such.

3) build a lamp bulb limiter, get a 40 to 75W bulb.

Power ON
4) plug amp into it and measure voltages indicated in schematic.
You wonīt get full +78V because of loss in bulb, but I expect around +50V there, +/- 10V.
Other voltages will be proportional.
Say, if you have +V=50V, then "10V" point will be around 7V and so on.

Post results.

Letīs normalize DC before messing with Audio.

That amp, if working properly, gives a very usable 100W into 4 ohms, around what any Bandit or similar amp delivers.

Thanks for the suggestions. I do have a lightbulb limiter and always use it when I suspect dead shorts. I have eliminated any shorts that I have and all of my DC voltages line up with the schematic. I have checked all of the resistors in circuit and a few with a leg up. None of the capacitors look blown out or anything either.

[g1]

With your same 140mv input signal, list the AC voltages for the following points:
Q1 base
Q1 collector
Q3 collector
Q4 emitter
Q7 collector

[antieatingactivist]

With your same 140mv input signal, list the AC voltages for the following points:
Q1 base
Q1 collector
Q3 collector
Q4 emitter
Q7 collector

Q1 base. = .125v
Q1 collector = 588mv
Q3 collector = 1.35v
Q4 emitter = 1.3v
Q7 collector = no voltage

Should I be getting something on Q7?

[g1]

Yes there should be AC voltage at Q7 collector. Q4 emitter has 1.3V and is connected to Q7 base. Do you have the 1.3VAC at Q7 base?
What are your DC voltages at E,B, &C of Q7 and Q8?

[antieatingactivist]

So I went ahead and changed the 2 drivers. I had an old Kustom PA head that met a firey end (reverb pan can detached from the lid of the amp and shorted everything out). I found 2 complimentary drivers and changed them and the amp is louder than it ever was! Other than the fact that turning the EQ off with the pedal causes a huge volume drop, I think its working properly. Thanks everyone, I learned a lot from this.

[g1]

Here are preamp and eq schematics. Do you still have a large volume drop when eq bypassed if the eq is set flat?