Homemade deluxe reverb volume problem

[Toxophilite]

I have a BF style one channel deluxe reverb with bias vary trem that I built in a hammond AO-43 chassis with the generous help of this forum. It has been a cool little amp
However lately it has started to do a curious thing...which is particularly annoying when practicing quietly in my apartment in the evening.
It dramatically increases in volume. Like somebody is rotating the knob up over a few seconds (I watched the volume knob, no paranormal activity) sometimes it jumps right up. Kind of crazy
I haven't opened it up in a while and the problem happens intermittently


Any idears?

[sluckey]

May be time to open it up. Thump some tubes.

[P Batty]

Bad connection/resistor in NFB circuit?