Awhile back I went to play through my rig and 20 seconds after firing it up the volume faded out. The first thing I did was change out all the tubes with ones that I knew were o.k. no change. I opened it up took a look around nothing fried. Then I checked to see if I was getting signal from the fx loop and I was, both outputs work, but neither the main outputs or the record outs are working (if I crank the volume I can hear a slight signal but compared to the fx loop it's barely anything). Any ideas?