Which tubes did you replace with the JJ's? Preamp out output section? I'm noticing that the controls on this amp are very interactive, more so than any other amp I've had. I had read about this before, but now I'm actually paying attention and am seeing it. I can eliminate the low E string flub by using less gain, and turning the bass knob way back - I don't really lose any bass output by doing this - there is still solid low end, but it takes the flub off.