SWR Super Redhead with power amp problem

[TASBrendan]

g1, Here's what I got running the variac for +/- 35VDC at the rails with Q6 removed
There's DCV on the output jack, but as I raise the variac towards 120VAC, the DC on the jack drops to 0. No smoke at R9, either.

Transistor readings at 35V rails for Q5, Q7-Q12:
Q4 CE = 2V, BE = 0.58V Q4 has the bias adjust, which is probably not set correctly right now.
Q7 CE = 26.15V, BE = 0.57
Q8 CE = -34.56, BE = -0.56
Q9 CE = 34.75, BE = 0.425
Q10 CE = 34.39, BE = 0.426
Q11 CE = 35.27, BE = 0.42
Q12 CE = 35.29, BE = 0.42

I'd say that looks really consistent. C6 tests correct value and low ESR

[TASBrendan]

Oh and Dude, thanks for the fan info- there's no 300R resistor on the fan circuit. I'll leave it jumpered. The owner says he runs it all the time.

[g1]

Q7 looks to be turned on much harder than Q8. The 10 volt difference would be dropped across R19 meaning 100mA through Q7.
Adjust the bias pot for lowest resistance between B and E of Q4, then recheck Q7 & Q8 voltages.

[TASBrendan]

Ok, got a new good MPSA56 in Q6 and retesting all the voltages running the variac for +/-35VDC at the rails.
Q6 CE = 0.89, BE = 0
Q5 CE = 0.86, BE = 0
Q7 CE = -34.22
Q8 CE = 34.86
Bias is set for lowest R at BE of Q4
Q9 - Q12 are all reading the same as before.

Think it's all finally looking good

[TASBrendan]

Slowly brought it up to full power on the variac and no smoke! Fan runs. Reading close voltages at CE of Q7 and Q8 and Q9 - Q12. No DC at the output jack. So far so good!

[g1]

When you get to the point of powering up with load, monitor the DC voltage across the emitter/collector resistors of the output devices. (R23-R26).
I would expect around 3 to 5 millivolts across each to be the ballpark bias setting.

[TASBrendan]

Q9 and Q10 are running 1 to 3 millivolts higher than Q11 and Q12. Biasing for 4mV at Q11 and Q12 gets 5-6mV at Q9 and Q10. Is it ok if the sides are off slightly like that? Everything else looks good. Thanks

[g1]

That seems close enough. I would go for 3mV at Q9 & 10, and increase only if I could hear crossover distortion at low volumes (or see it on scope).

[TASBrendan]

I'll double check the numbers and check it on the scope, but so far at low volume sounds good!