I recently picked up a used Rockytop JTM45 clone. It sounds great before it breaks up, but when I crank it there's some weird fizz/ghosting on the notes. Also, I noticed that the Valve Arts KT66 power tubes flash purple inside of them when it's cranked each time I hit a note. I've never seen that on any amp I've owned before. Bad power tubes? Poor bias? I'm weary of using it until I know what's going on. Any insight would be appreciated.