Fender Custom Vibrolux RI question

[Randall]

Riddle me this. When I freeze C17, the plate pin 6 of V2 goes crazy noisy, and grounding grid 7 or turning the volume down stops it. I don't see how this could be?

https://www.thetubestore.com/lib/the...-Schematic.pdf

[Helmholtz]

When I freeze C17, the plate pin 6 of V2 goes crazy noisy, and grounding grid 7 or turning the volume down stops it.

Could be caused by condensed moisture, providing a leakage/creepage path. Should stop after drying.

What's the problem with the amp?

[Randall]

So far it looks to be three bad caps. Problem it came in with was random squeals, groans, and slow siren sounds. C8 was leaking DC onto the bass control, and getting to the volume control. C9 was causing a lot of random noise that would come on for a while and then stop like a switch was thrown. Those two I understand would be effected by the volume control. Once I replaced them, most of the noise stopped unless I freeze C17. It causes more noise than is acceptable as it warms up, so that one is getting replaced next. I still don't see how that noise goes away when volume is turned down. It's not moisture, I am pretty confident of that. It's dry season here, and this is pcb reissue.

[nosaj]

I think he was talking moisture creating condensation from the freeze spray.
nosaj

[Helmholtz]

It's not moisture, I am pretty confident of that. It's dry season here, and this is pcb reissue.

The moisture condensation is caused by the freezing.

[g1]

The moisture from the freeze spray is just a temporary thing as it warms. The temporary paths created are probably why it is getting back to before the volume control.

[nosaj]

So if you DON;T do this
most of the noise stopped unless I freeze C17. It causes more noise than is acceptable as it warms up, so that one is getting replaced next.


How does the amp behave?
nosaj

[Randall]

Ah, yes. Freeze spray moisture. I still don't think it is that since the C17 is located alone on the board, not really near anything.

BUT, it is now quiet after replacing the three caps. Curious that three different brand caps would be bad like that.

[Helmholtz]

I still don't think it is that since the C17 is located alone on the board, not really near anything.

The moisture path would be between the legs of C17, leaking high voltage from the plate side to the grid.

To be clear, the moisture is not contained in the freeze spray. Rather the low temperature makes residual air humidity condense.
It first shows as white snowlike ice, then melts to water droplets.