hey all, i'm lucky to have a glorious sounding magnatone that has some strange issues that cant be tracked down. after several techs and over $1000 spent there is still an issue that cant be solved; the last guy i brought it to refused to even work on the amp when he saw it its a pretty complex beast http://www.magnatoneamps.com/M20.html the power section has been recapped and all tubes replaced several times. my biggest concern is that the reverb will intermittently slowly self oscillate/feedback into a low tone, i think it was around a B note. It gets quite loud, about as loud as the guitar signal itself. It stops if i turn off the reverb, but will usually quickly return once its started. the thing is i cant reproduce it when i need to, like showing a tech - it wont happen for a week and all the sudden it will start every time i use reverb. It happens with no input signal, sometimes on a cold amp but more often than not after the amp has been on a while. also, i dont know if its related but turning the reverb on sucks a fair amount of treble and adds bass to my tone. i also seem to have a grounding issue on the bass input jack, as that channel has fairly loud hum unless a jack is inserted halfway - its the last channel in the circuit right before the reverb i believe. i feel like it could be related somehow but none of the techs ever fixed it. if anyone has had a similar experience or any advice on where to look it would be much appreciated. .