Johnson Stage 100 AR pops and it's distorted

[Garydean]

I have a Johnson SS here that has full output volume but....no matter how the controls are set it's slightly distorted, not clipping, OP amp issue? What stage should I be checking. Inject a signal from the power transistors and work my way to the input till the signal gets distorted?? AND at power down, there is an audible loud pop, with or without a signal. If I turn the "level" knob to zero, I get no pop. The gain function does not effect the pop at shut down. When I engage the "notch" button, the pop changes to a winy fizzle and fades away.

Do these amps shut down this way?

Thanks