I have an ongoing issue with my CTM-15 where the amp is producing beautiful sound and then it just cuts out. Not completely, it's still producing sound, but at a significantly reduced volume. It seems to take an hour of playing before it starts being a problem. Here's what I've tried so far before coming to the conclusion that it's in the amp. Cables - tried 4 different instrument cables (bass straight to amp), and I was able to replicate the problem each time. I checked the cables with a multimeter too, all OK. Bass - I tried 3 different basses (active/passive), and was able to replicate the issue with each instrument. Amp - I changed out the preamp tube over Christmas, and when I have practice on Tuesday, I'll swap out the tube to see if that's the issue. These amps have an analog input meter on the face, and when the volume drops the signal meter also goes to hovering around -20dB. I'll welcome other thoughts while I wait to change out the preamp tube.