Hey, ive just brought a Traynor YCV40T and its great. but i was wondering could i interchange the 6L6s that are in it for say.. EL84s, KT66s or EL34s in the future? its auto re-biasing if that helps.. would they actually fit and how do i go about changing tubes if they do?
i said "come on lets dance, we've gotta take our chance" u whispered in my ear "you wanna get outa here?"
I just posted a similar thread. My question is not much different than yours, however, I can tell you this:

An EL84 will not work. It has a different socket, or pin layout.

The remainder of power tube designations at least share the same base. I am not familiar with your amp, but if it really is automatically biasing, then I would suggest giving other tubes a try. www.eurotubes.com sells JJ-Electronic tubes (the only alternative to NOS domestics, imho) and offers a brief description of the differences in sound between power tubes if you go through the shop online link and look through power tubes.