I've been buying tubes for about 5 years now and I'm swimming in the things: mostly 6v6s, 6L6s, 12ax7s, 5v4, 5y3, 5u4 - one of the few things did right in my life was to start buying old tubes when they were still affordable - the difference in a tube amp is substantial, though there are finally a few new production tubes that make the great - primarily Tad 6v6s and 6L6s - still, a a lot the old stuff is affordable on ebay (Mullards NOT included) bt you do fine with GE, Sylvania, Raytheon, Scott - it's a brave old tube world out there - just got an amp with 6sl7s and 6sn7s so that's my latest obsession -