I play a 1970s 212 HD 130 with the 12ax7 phase inverter.
I posted a few months ago about an intermittent static issue I was getting. I seemed to resolve that issue by re-flowing the solder connections on a few suspicious looking spots.
The amp has been playing relatively well since then. However, I have recently noticed a new sound creeping up every now and then. It's pretty annoying. It's kind of like static or fizz that breaks through the normal signal. The static I was getting before showed up regardless of whether I was playing or not. This static seems only to appear when I play.
Follow this link to hear a sample I recorded:
Noise can be heard from about 3 seconds to 10 seconds.
At 35 seconds I switch from low power to high power.
Noise can be heard again from around 41 seconds to 52 seconds; 1:36 seconds to 1:38 seconds; and at other times til the clip ends.
I would love to hear from those with more experience if you've ever heard a noise like this before. It may help save me a little time trying to diagnose it myself.
My guess for now may be a bias issue. I notice that my bias reading fluctuates from .50 down to .492 and up to .530 sometimes. Is it normal to see the bias fluctuate like that?
I have materials here to create a signal tracer. That may be my next adventure.
Any other thoughts or suggestions would be appreciated! Thank you!