Scully 280b Line Amplifier Troubleshooting

[Joefis809]

Looking for some help troubleshooting the line amp part of this circuit. Not an expert, looking to learn what I don't know...

See attachment- I've got signal at Q13 base, but there is no output. All transistors have been replaced and I've also tested, all working correctly. Q10 and Q11 have been replaced with NTE 2658/2657 respectively.

+/-25V supply are correct. The voltages written in parentheses are from the other channel which is working fine. I am seeing +24.5V on base and collector of Q9, and am not sure why. Looks like a short, but I've gone over this with very close eyes. Any ideas where to look next?

 

[Joefis809]

Update: I've salvaged a D41D7 and replaced Q10 with that and Q11 with a new D40D7 (which I have a handful of NOS), and it works. Of course D41D7's seem to be long gone.

So, do I need to compensate for the 2657/2658 with different R Values? Is there a better alternative to the D40D series transistors I should be looking for? I was told by NTE engineer that the 2657/8 were acceptable replacements, and from what I've researched this seems correct. What's going wrong?

 

[chops]

The folks at https://groups.io/g/scullyrecorder

will sort you out.

 

[JohnRoberts]

I can't make sense of your noted voltages but troubleshooting discrete transistor circuits begins with looking for proper junction voltages. A biased on base-emitter junction will drop approximately 1/2 V.

JR