There are so many variastions, I have only scratched the surface. So far,
CBS (or Raytheon) 5814 (blk plate), RCA 12au7 - both clear top and blk pate, Matsu****a 12au7, TS 12au7 (blk glass) is my favorite.
I just started with 12bh7 and like the few I have tried. Also 6211 and 5963 is interesting.
Above also depends on what output tube etc. it is combined with.
Sometimes, I am not sure if I am looking for something I like more or just enjoying the variation
