If it only uses one 6V6, that's where I'd try a variety of brands. No need to worry about matching. Singles are usually much easier to find. I have a ton of old pre-amp tubes. One that sounds awful as a reverb driver could make a great phase inverter, and vice versa, and it has little to do with the brand. Yes, a good old RCA, Tung-Sol, Raytheon, or Telefunken is a thing of rare beauty, but a stinker is a stinker no matter what's printed on it. Testing usually won't reveal whether a tube is microphonic, so it's a gamble when you buy venerable old brands at astronomically high prices. I like Tung-Sol "reissue" 12AX7s a lot. EH are nice-sounding, but I had a few fail quickly. JJ has started making what some users are saying is by far the best AX7-type in many years, the E83CC (not ECC83), so that may be worth checking out; I haven't had the opportunity yet. For 12AT7s, NOS are still worth it, and Sylvania JANs, Telefunkens, and Westinghouse blue label (mid-sixties) are my favorites, although GEs are pretty nice too. The 6201 designation is a major plus; it means lower noise and tighter tolerances. A NOS 5AY3 won't kill your budget and is definitely worth considering. Even if you don't need 'em now, a full complement of tubes is good to have as backup.