Thanks @indianajo. Your cinch terminal sounds ike a good idea. The layout of this thing stinks, the entire output stage is inaccesible without tearing it down. I think that's why their bias instructions says to measure it from the -V tap at the diode bridge.
I found two sets mj15003 / mj15004 transistors last night. In the 80's and 90's we used this amp for production testing and kept spares on hand. FWIW, I recall it being a very reliable unit. I have a DVM which uses 4.5V for diode test, I'll try that one on the suspect ones first.
But I suspect, as Mooly suggested, that it's not the outputs, but a common problem upstream. That guided my thinking that, since the supplies are separate, to disconnect the output stage power supply and power up just the preamp section to check the low-level stuff first.
I found two sets mj15003 / mj15004 transistors last night. In the 80's and 90's we used this amp for production testing and kept spares on hand. FWIW, I recall it being a very reliable unit. I have a DVM which uses 4.5V for diode test, I'll try that one on the suspect ones first.
But I suspect, as Mooly suggested, that it's not the outputs, but a common problem upstream. That guided my thinking that, since the supplies are separate, to disconnect the output stage power supply and power up just the preamp section to check the low-level stuff first.