Hey all

I just picked up a silverface fender twin FREE from around (im guessing) 1978, it has stock tubes, stock JBL speakers, damaged tolex and grille cloth, damaged knobs.

the problem is that the tone is really flabby and undefined, and highly compressed, most likely because of those old tubes, but i was wondering what else it could be (speakers, caps/resistors, circuitry).

the tone i get through a gibson sg is really loose bass, strange highs (2nd and 3rd strings are stupid loud but then seem to get a compressed sound) and a decent, but compressed mid range. When i use the amp's boost feature I actually kind of like the tone since im into grunge and the tone is like a rough-cut distortion, but its inconsistent and really annoying. The overall tone doesnt respond well to dynamics, is inconsistent and not smooth by any means.

sounds like old tubes? im not sure... (im looking at 4x JJ 6l6gcs with 6x tung-sol 12ax7s)
also, how would it benefit from some new celestions for metal and grunge?