Sunn Beta Lead - Distorted, low output

[stereomonostereo]

I'm at 0.8v at the base of Q8. R21 and R50 are reading 0.3mV across

[g1]

And does the bias adjustment now work?
Can you get the Q8 base voltage to rise and more like 5mV across R21 and R50 ?

[stereomonostereo]

The bias adjustment just takes me from 0.3mV down to 0.0mV across R21 and R50

[g1]

What are your Q8 voltages?

[stereomonostereo]

Q8 reads

C: +42
B: 0.79
E: 0.43

I should be seeing 1.2 at the base

[g1]

Q7 voltages? e,b,c and then b voltage at both end settings of bias pot.

[stereomonostereo]

Q7 reads:

E: +42
B: +1.4
C: 0.7

The base ranges from +1.4 to -1.1 with the bias pot

[g1]

Q13emitter (Q7 base) should be able to go more positive than 1.4V.
What are E,B, and C for Q5 and Q14 ?
Do R13 and R38 check good?

[stereomonostereo]

Thanks for bearing with me.

Q5:
E: +42
B: +41
C: +1.4

Q14
E: -42
B: -41
C: -1.9

R13 and R38 are both spot on

[g1]

Sorry but this one has me kind of stumped. I'm hoping someone else here might have some ideas.
Meanwhile, that schematic is split right in the area we are concerned with and that's really irking me. So I cobbled one together that I hope is legible. I guess not because the one in the pdf is poor to begin with.


The problem seems to be that it is unable to develop enough voltage across the bias transistor (Q13) to result in turning Q9 & Q10 on. We need to at least get a few millivolts across R18 or R21.
Just to rule out a limiter/clamp malfunction, try removing Q8 (BC107) and see if it changes the bias range.

[Enzo]

This might be better copy.

You got 30v at collector Q1? 15v at emitter?

Same at Q11, got -30 and -15?

Got the DC voltages at Q13? And at Q4, Q12?

Cram a volt of signal into the input. Does it come through at the TPs?

Look on any pin of the boas transistor for signal. Whatever signal level you see there should be the same level as the output. SO if minimal signal exists there, don't expect any more on the speaker.

IN a crude sense, everything top the right of the bias transistor is a current amp, and everything left is the voltage amp.

[g1]

Enzo, that is a much better drawing, thanks.
His DC voltages are all mostly good, Q13 emitter a bit off resulting in not being able to turn the positive outputs on.
He gets max. 1.2VDC at Q13 emitter when adjusting bias trim, nothing across emitter resistors of positive side outputs.

[stereomonostereo]

The signal is strong on the bias transistor, as well as TP-4 and TP-5. However, it's weak and distorted on the emitters of Q7 and Q16.

[stereomonostereo]

And i'm also noticing now that CR2 and CR8 are 1N4148 diodes instead of 1N458s that are shown on the schematic

[g1]

Those diodes should be fine. I'd suggest temporarily removing Q6 and Q15 limiters to see if any changes.
Something is stopping Q7 & Q16 from conducting properly. Are all transistors the type shown on schematic or have there been any subs?