My Peavey Classic 50/50 tube power amp finally came in Saturday. I put in some new JJ tubes as soon as I got it and had band practice that night, and it worked flawlessly. Until I tried to set it up different. I did have it running stereo, but then tried to run it mono, and no sound would come out o fit. Everything turns on fine (I haven't opened it back up yet, but even then I wouldn't know what to look for), I just don't get any sound. I ended up having to use my classic 50 combo amp for my power amp for last nights practice. Any idea's why it's not sending a signal/power to my speakers?