My rig is a Conklin 7 into a tech 21 sans amp rbi into the power amp in on the back of my 750x head. Ive run the heads volume at 3 and 4 oclock all the time for years into a swr 610 and an ampeg 810 and its ******** loud and has never crapped out. Maybe you need to turn down the limiter knob some. The power amp in the 750x is as solid as they come . I got mine right when the x came out and the only issue I had was the preamp tube doesn't last ( as no tubes last forever) and changing the tube always seemed to give a different sound. So the sans amp RBI fixed that.
