I'm in the process of creating a schematic, not fun.
Once I have a basic flow I can have a better idea of what is going on.
In testing I see a clean sine wave going in and a clipped sinewave coming out.
I'll have to research how to determine if it's a NPN or a PNP transistor.
As I recall it has something to do with polarity at the E or C terminal.
At least on the back side of the pcb, are the letters E B and C, in most cases.
so that helps
Being an audio amp, the choice of available parts is sizable, I can scan the NTE database and probably find something.
I suspect that I just need to take a series of voltage measurements then select a part that has spec's that exceed them by 10 % or so
But I've never had any sucess in part subsitution.
To add to my pain, I haven't done analog service in over 30 years.
Other than replacing old caps, resistors and a few blown xformers with new in a old McIntosh tube amp.