Just bought a Fender 57 custom Twin off reverb. Previous owner shipped the amp with tubes still in their sockets. Not great but it worked fine when it arrived so I kind of overlooked it. Now about a month later I’m noticing the amp kind “glitches” out when I play harder. Like when I strike a chord at first it sounds like TV fuzz for half a second and then cleans up again and sounds normal. Happens especially when I’m running a gain pedal. I’m thinking some of the tubes need replacing. Any idea which ones? Could it be power tubes? Rectifiers? Running a little low on funds since buying the amp and would prefer not to replace all the tubes right now if I can avoid it.