For op-amps in a circuit that uses local feedback (this circuit), the output and inverting input of each op-amp section should closely match the non-inverting input.
That's essentially what you have.
The voltage that you saw change with the gain selector change is due to a change in local feedback.
Without a scope, it's difficult to know for certain whether the amp is 100% healthy. It likely is if it sounds OK, especially with the numbers you last posted.
That's essentially what you have.
The voltage that you saw change with the gain selector change is due to a change in local feedback.
Without a scope, it's difficult to know for certain whether the amp is 100% healthy. It likely is if it sounds OK, especially with the numbers you last posted.
Did your tester see the TIP107 as good and the original as bad?
Yes.