70's silverface Twin Reverb squealing

[booboocakesjones]

Once I hit a certain volume (around 3 but through a full drive pedal) the amp starts this satanic sounding (and very loud) squeal. high pitched and middy, but once it started it would not stop until i hit standby. then it was gone until I hit the same volume again. I made sure it was not a cable or the pedals, by isolating these/switching out. I have not changed the tubes in about 3 years, since I've had the amp... Do you guys think that's the problem? Oh and it's not through the reverb channel but the one on the far left.

Thanks!:confused:

[Bruce / Mission Amps]

Once I hit a certain volume (around 3 but through a full drive pedal) the amp starts this satanic sounding (and very loud) squeal. high pitched and middy, but once it started it would not stop until i hit standby. then it was gone until I hit the same volume again. I made sure it was not a cable or the pedals, by isolating these/switching out. I have not changed the tubes in about 3 years, since I've had the amp... Do you guys think that's the problem? Oh and it's not through the reverb channel but the one on the far left.

Thanks!:confused:Sounds like it could be a bad preamp tube.... replace the very far right one as viewed from the back.

[booboocakesjones]

will try this