It started recently. I guess this means my bias has drifted? It sounds pretty sweet. I'm pretty sure the trem is bias modulated but I'm not certain as Nik has never been clear on this that I can tell.

I'm considering simply removing the trem. After studying the layout it looks really simple. I have a trem pedal (SD Shape Shifter), and it would free up a perfect spot for the Dana Hall VVRIII voltage scale control which I want to add.

After more than a year, this remains a GREAT amp, and the glitches have been few: loose KT66 base, superglued; replaced ON lamp (thanks again Hiredhand!); loose wire on input jack, resoldered etc.