[Niteshade]

Just wondering- has anybody ever set up a negative feedback circuit in a tube amplifier and have it squeal? If so- how did you fix it?

[bricktop]

Yes, I do a lot of experimentation.

Lessen the feedback ratio, use a different form of feedback (i.e. interstage), and make sure it is of the proper phase.

[jon_010101]

And, don't forget grid and screen stoppers on output tubes if not presently in place. 

[Niteshade]

Thank you!   

I know what I was doing wrong now. Will let you know how it works after the mods...

[Niteshade]

I checked the circuit and the grid stoppers, etc.. were fine. That's not what was causing the NFB squeal. I swapped primary leads between the plates and that's what fixed it. So- it was a phase issue.

[Steve]

I checked the circuit and the grid stoppers, etc.. were fine. That's not what was causing the NFB squeal. I swapped primary leads between the plates and that's what fixed it. So- it was a phase issue.

Glad you found and corrected the problem. Happy Tunes.