I have a JSX and I know its rated at 120 watts. So my question is can I put a quad set of KT88s in the amp and have it work or would I have to have it modded in order for it to take KT88s?
You'll need to have it biased for KT-88s, that is if the power transformer can even deliver enough power for them.
im pretty sure you would have to get it modded, but im not 100% sure. I would give a call to Bob at eurotubes. He shouldn't mind if you plan to get the tubes from him, and is a pretty helpful guy anyways.