Silvertone 1474: Sounds like DC on a pot but...

[Ptron]

Here's the schem.
http://www.freeinfosociety.com/elect...ertone1474.pdf

O.K., It's not a thunderous noise but the channel two volume pot is really scrathy when it's turned. If I turn it up and leave it it's a little bit noisy but it's only when turning it that it's really bad. I replaced the pot. It didn't help. I didn't read any DC on the pot but I replaced the .02uf coupling cap from V1 anyway, still didn't fix it.

Here's the catch: If I pull V1 and continously turn the pot it will continue to be scratchy for a few seconds and then slowly fade. I tried different tubes.

What could be causing this? The components are a PITA to replace in this guy so I'd thought I'd ask before I do a shotgun replacement of the pre parts. Sorry if that's being lazy.

[Enzo]

Notice how the Channel 2 volume pot is the ONLY return to ground for the grid at pin 7 of the tube next to the reverb. The grid naturally accumulates a small negative charge on its grid through "grid leak." I'd wager that is what you are hearing.

See how the Channel 1 volume control doesn;t have to be the grid return for its circuit.

Try adding a large value resistor from that pin 7 grid to ground - 1meg, 2meg, something. And also add a largish cap between the wiper of the volume control and the rest. I don;t know, maybe .047 or .1, maybe even smaller. I just want it large enough to not roll off any frequencies we care about. You could lift the wire off the wiper, solder the cap to the pot terminal and the wire to the other end of the cap.

See if that works for you. You would then have a grid return for that grid, independent of hte pot, and the pot would have DC isolation from the cap.

[Ptron]

Notice how the Channel 2 volume pot is the ONLY return to ground for the grid at pin 7 of the tube next to the reverb. The grid naturally accumulates a small negative charge on its grid through "grid leak." I'd wager that is what you are hearing.

See how the Channel 1 volume control doesn;t have to be the grid return for its circuit.

Try adding a large value resistor from that pin 7 grid to ground - 1meg, 2meg, something. And also add a largish cap between the wiper of the volume control and the rest. I don;t know, maybe .047 or .1, maybe even smaller. I just want it large enough to not roll off any frequencies we care about. You could lift the wire off the wiper, solder the cap to the pot terminal and the wire to the other end of the cap.

See if that works for you. You would then have a grid return for that grid, independent of hte pot, and the pot would have DC isolation from the cap.

Bingo!

Thanks Enzo. I'm really glad now I asked before I started randomly replacing parts.