I picked up a semi-operational clean blackface Vibro Champ at Pawn City. (It went something like: PS- Thats the only amp we got, sometimes it works, sometimes it don't. JR- What do you do to make it work? PS- I bump it (no effect) or hold the speaker wires like this (2 draw booms out). JR- Here's the fourty bucks.)
My question is- Are there any worthwhile tube substitutions or other (preferably reversable) modifications to optimize for harp?