Amen to that- the working unit to compare!

I finished the Dynaco ST120 from hell last night. It came to me "fuzzy in one channel". And it was.

First run-through: One output transistor in the 'good' channel, one output and one driver in the other, still fuzzy. I wound up ohming out every part, comparing to the good channel. Six drifted resistors later, I got to the 5..1V zener diode. Bingo. It had become a 94 ohm resistor.

Given that these beasts blow up by the numbers, I generally install sockets for the outputs, and do the TIP mod once ALL else is under control.

Peter Wieck
Melrose Park, PA