ROFL, while crying at the same time. Many months ago, I sent my RH750 in to have all the buttons and knobs replaced. I got it back a couple weeks later, but didn't even plug it in - it just went in its case. So, after coming across this thread tonight, I decided to unhook my TH500 in my practice room and give the ol' RH750 a spin. After I got it set up on its cab, I adjusted the gain knob, which immediately split completely in two and fell into my hand. I barely touched it. So I tested the other knobs, and each and every one except the volume knob slid right off the shaft, several after one of the little internal vanes broke.
Fortunately before I sent the amp in, I had complained to TCE about the problem, and they sent me another set of knobs which came in while my amp was at their service center. So I was able to put my reserve set on without incident, and they seem to be working, but now I feel vulnerable - I have no backup position. To be fair, TCE's customer service has been fair and prompt to respond. But as good as they are, I'd rather not be talking to them, and I'm sure they feel the same way.
So. TCE representative, if you're out there, listen up: THIS IS A SERIOUS AND PERVASIVE PROBLEM! WHY THE HELL HAVEN'T YOU FIXED IT?
<edit> OK, OK. I'm grumpy right now. This is the third set of knobs I've had on the amp. Plastic knobs retail at about 50 cents apiece. That means it costs less than a dime each to manufacture them. What would be wrong with finding a vendor who can provide the quality of knobs commensurate with the amp's quality and have them produce a different knob that will fit on the existing pot shafts? That design with the little vanes inside looks like something the company assigned to a brand new ME graduate as a first project. Well, he failed. It's time to correct the problem once and for all. To me that means a redesign of the knobs to something robust. I've owned (and still own) a lot of amps, and have never encountered a problem like this. Once you have a dependable design, you could offer the new knobs to existing owners by publicizing it here. I can't imagine it would cost you more than a few thousand dollars to make this right.