Static - Bad OT?

[lowell]

Got a Music Man HD212 that has static on grids of power tubes but NOT before that. Replaced all wires, trouble-shot bias supply, replaced tube sockets, tubes... at a loss. Only thing left is OT. Anyone ever replace an OT due to this? Could a bad OT cause this?

[booj]

Is it a one-thirty?. One model has a tube driver. One has the cathodes of the power tubes driven with power transistors.

[Enzo]

What do you mean the only thing left is transformer?

I didn't see bad coupling caps from the earlier stages.

Pull the power tubes - is that noise still on the grid pins of the empty sockets?

[lowell]

Enzo sorry forgot to mention I disconnected the PI coupling caps and static was still there.

[52 Bill]

Did you check the screen supply caps and resistors?

[lowell]

Yes I replaced them and the screen filter cap.

[Enzo]

Do you have any other output transformers around? Don;t worry about the impedances, we don;t care about distortion at this point, all we care about is does it make noise. Disconnect the existing OT wires from the B+ and tube sockets, clip or temporarily wire in the other transformer and clip a speaker to its secondary - don;t hook up the existing secondary stuff. Does it make static now?

I have an old Fender Bassman transformer I use for this test.

[melvin]

what about static on the bias?

[melvin]

Pull the power tubes - is that noise still on the grid pins of the empty sockets?

just confirming, not the case?

[Enzo]

What melvin said.

If the coupling caps are lifted and the tubes are out and the static remains, it has to come from somewhere. If it isw in hte bias supply, that would make sense

[lowell]

What melvin said.

If the coupling caps are lifted and the tubes are out and the static remains, it has to come from somewhere. If it isw in hte bias supply, that would make sense

Well I don't see it before the 330k bias feed resistors. I have also replaced the bias filter cap and pot.

I'll try the sub OT.