Blackface Vibrolux Clone - Static from both (new) volume pots

[acorkos]

This amp had a few problems which I think I've solved, but one that is remaining is relatively loud static when I turn the volume pots, both NORMAL and VIBRATO channels. The builder used several old Astron and blue Molded caps in the tone stacks and other parts of the signal chain, I'm not sure if they are the problem or is there something further down the signal path causing a problem on both the volume pots...they are both new, just installed (by me) BTW. Any ideas on where I should look? Thanks for your help

[acorkos]

Also, the voltage on pin 1 of both V1 and V2 are ~100 volts higher than on pin 6 of both tubes

[drewl]

Any dc voltage on the pots causing the static?

[acorkos]

There is up to 300mv DC on each volume pot when the pot is wide open...this is with all new tone and coupling caps and new tubes.

[g1]

Is it through the entire range of the pots, or just the top half?
I just went through the same thing on a silverface putting in new alps 1M volume pots. They were noise free being turned up to about 6. But turning them from 6 to 10 they were noisy. It was the pots, just the way they are made I don't know?
But they sounded fine when not being turned so I let it go.
Had about the same amount of DC that you have.

[acorkos]

it's through the entire range, both channels, from zero up to about 450mv, backing off to about 400mv as you get up to 9-10 on the dial

[g1]

Also, the voltage on pin 1 of both V1 and V2 are ~100 volts higher than on pin 6 of both tubes

This sounds odd, wondering how much of an exact clone it is.
Do you have a schematic that matches exactly?

[pdf64]

If the triode section following the vol etc control has excessive grid current, then the controls will exhibit that noise when operated.

[acorkos]

I found the culprit....the cathode bypass cap shared by both channels (V1-8 + V2-8) was bad....I replaced it and the noise (and voltage leak) is gone

[Chuck H]

Ok... I'm honestly not stirring "s" here... Just asking a question I don't know the answer to.

How does a shared cathode bypass cap cause grid voltage? Bypassed or not? Almost half a volt of grid DC is enough to mess things up for certain. How could the cathode bypass cap being bad cause this?

[pdf64]

All I can think is that it was bad 'shorted', rather than the regular bad of cathode bypass, of high ESR.
The 'no bias' condition (and also resultant low plate voltage) may cause a lot more grid current, as per grid leak bias.