Blues Junior distortion

[OldFarb]

This is a 2006 BJ in Tweed with the Jensen C12n. Playing 2-3 strings together, I hear a slight raspy distortion as the notes fade. I replaced the tubes and tried another speaker, ran another amp through the Jensen. No luck, it happens on any speaker and the Jensen is fine with another amp. It's not very loud but it's there.
Does it with and without reverb, Master Vol is wide open and I use the Fat switch. Tone controls are set generally around their midpoints.
Any ideas?

[Gunny]

Sounds like a very common BJ amp symptom. The remedy is described in great detail at BillM's site http://billmaudio.com/wp/?page_id=115

This fix does work.

[OldFarb]

Thanks, Gunny. I've read through BillM's site before but missed that one. I'll try it tonight, appreciate the help!