Ampeg Reverberocket 12RT Troubleshooting

[Steelwitch]

Could it be oscillation from the Reverb tank?

[Steelwitch]

After some more tests, I think it could be an issue with grounding. Once the oscillation happened, I checked the AC voltage on V4 and V3, oscillation stopped after being grounded through the meter

[g1]

Does it do this with the reverb turned all the way down?
And it only does it with a speaker, not into a load resistor?

[Steelwitch]

I ruled out the reverb theory I think. It only happens with a speaker, not the load!

[Steelwitch]

I just took voltages on the tube socket I was considering replacing and everything looks normal. There is definitely signal loss when it happens and maybe in general!

[Steelwitch]

It also continues with the volume all the way down although, decrerasing the volume affects the speed of the oscillation. I just signal traced the entire circuit on a scope and everything looked ok.

[Helmholtz]

I ruled out the reverb theory I think. It only happens with a speaker, not the load!

If the speaker is placed close to the amp while testing, try to increase distance and ground the speaker chassis.

[Steelwitch]

If the speaker is placed close to the amp while testing, try to increase distance and ground the speaker chassis.

Right now they are both in the cabinet! If anyone has recommendations for testing bad grounding, at least to rule that out, I'm all ears!