I was that guy, when it came to 6SN7, 6SL7 and their variants. The generation before the 6SN7, the 6J5-G and the 6J5-GT, each of which equals one half of a 6SN7 were better through 2 for 1 adapters. My best tubes are my RCA 211, black plates circa 1943. Because I went through 7 tube testers, I...