EL34 Grid Stopper resistor

[ca7922303]

Disconect the PI outputs to power tubes. It still osscilate? If Yes than check the OT wiring track (keep away ot primary wires from inputs wires, secondary common directly to output jacks and from those point to nfb retour) . 100 ohm screen grids close to the socket should be able to cure any . If osscilation stoped with PI disconected check then the PI stage. First wiring track, specially the wiring from OT to nfb injection point.

Would disconnecting the yellow and white wire that go to V6 pins 9 & 5 disconnect the outputs to power tubes?(photo).

[ca7922303]

Would disconnecting the yellow and white wire that go to V6 pins 9 & 5 disconnect the outputs to power tubes?(photo).

They are connected to pins 2 & 7 on V7/V8 sockets.

[catalin gramada]

Be aware to not disconect at power socket. You will leave the power tubes without bias reference and blow it. Just one end of coupling caps.

[Chuck H]

Only way I know to describe it is a high pitched squeal that increases as drive/volume and master volume are about on 10. It's accompanied by both tubes red plating and output loss of power.

This sounds like an ultrasonic oscillation due to instability at higher drive levels. It's likely due to lead dress, grounding or insufficient decoupling in the power supply. Something later in the amp is "talking" in like phase with something earlier in the amp with the controls set for more sensitivity. This can be caused by like phase leads in proximity to each other, shared ground leads for like phase circuits with enough resistance for a little signal to ride on them or like phase amplification stages on the same power rail node that is not decoupling signal well enough.

[ca7922303]

Be aware to not disconect at power socket. You will leave the power tubes without bias reference and blow it. Just one end of coupling caps.

If I understand you correctly, I shouldn't disconnect the white and orange wires connected to V6. Can you describe where I should disconnect PI from power tubes?

[Chuck H]

Would disconnecting the yellow and white wire that go to V6 pins 9 & 5 disconnect the outputs to power tubes?.

You did not supply a schematic in THIS thread for V# references. But...

If V6 is the PI tube then what you propose would disconnect the filament circuit.

They are connected to pins 2 & 7 on V7/V8 sockets.

If V7/V8 are the power tubes then, again, you would be disconnecting the filament circuit.

DO NOT do either of these things.

[catalin gramada]

If I understand you correctly, I shouldn't disconnect the white and orange wires connected to V6. Can you describe where I should disconnect PI from power tubes?

You should identify c18 and c19 on the board 100nF/400v . Just lift one end from each to isolate PI from power stage. You should be able to locate the source of oscillations. Let try different: Did the power tubes red plating with v6 removed ?

[ca7922303]

You should identify c18 and c19 on the board 100nF/400v . Just lift one end from each to isolate PI from power stage. You should be able to locate the source of oscillations. Let try different: Did the power tubes red plating with v6 removed ?

Can I remove V6 tube only? The white and orange wires connecting V6 to V7/V8 or something else?

[Chuck H]

Can I remove V6 tube only? The white and orange wires connecting V6 to V7/V8 or something else?

See post #21 !!!!!!!!!!!!!!!!

If you're going to ignore me I'm leaving.

[ca7922303]

See post #21 !!!!!!!!!!!!!!!!

If you're going to ignore me I'm leaving.

Not trying to ignore. Got your posts after I sent mine. Will not disconnect. Trying to clarify what other one was saying. I think there is a language barrier and my inexperience causing confusion.

[catalin gramada]

Can I remove V6 tube only? The white and orange wires connecting V6 to V7/V8 or something else?

Yes take it out and see if power tubes still redplating. I don't have the whole picture of you amp but still may try to isolate the problem. Did you checked the bias of power tubes ?

[Chuck H]

Well you have another (enormous) thread for this amp. But remember that information you've given there is not presented here. And, I'm probably not going to peruse that thread thoroughly for bits of information because it would take an inordinate amount of time. So...

Have you replaced any electrolytic capacitors in the power supply for this amp?

[ca7922303]

Well you have another (enormous) thread for this amp. But remember that information you've given there is not presented here. And, I'm probably not going to peruse that thread thoroughly for bits of information because it would take an inordinate amount of time. So...

Have you replaced any electrolytic capacitors in the power supply for this amp?

Yes, I believe C37 which is near R43. I'll send you a link for schematic I have.

[ca7922303]

Well you have another (enormous) thread for this amp. But remember that information you've given there is not presented here. And, I'm probably not going to peruse that thread thoroughly for bits of information because it would take an inordinate amount of time. So...

Have you replaced any electrolytic capacitors in the power supply for this amp?

https://acrobat.adobe.com/link/track...0-ad65930e0bba

[Jon Snell]

Seem to be wandering about all over the place.
The original question was ... ? ... no idea, it has gone on too long and is hitting deaf ears. From memory it was adding a grid stopper but there already is one and now it seems it is oscillating ..... why are you disconnecting the heater supplies?
I'm gone.