Any rig doctors in the house? Last night, I gigged for the first time with my SWR 550-X and 6x10. During the second song, all my volume suddenly disappeared. The lights on the amp and power conditioner were still on, and my cable was firmly in the bass and the amp's input. I turned the amp off and back on, and the volume came back. Two songs later, it happened again. This time, I had to turn the amp off and back on twice before the volume came back. That was the last time it happened, but it affected my playing for the rest of the night because I kept looking back at my amp to make sure everything was OK. This same thing happened in my basement a few weeks ago.. I was jamming, and the volume disappeared. I changed basses and cables, nothing happened, and then I turned the amp off and on, and the volume came back. Has this happened to anyone else? My first thought is, the preamp tube needs to be replaced. I bought the amp used from Guitar Center. I wasn't clipping the preamp last night, but the limiter light was flashing fairly consistently. I had the gain on 6 or 6 1/2 and the master on about 4 1/2. There was no P-A for the bass, so my stage volume was for the crowd, too.