The EH 6CA7s are some of my favorite power tubes. I have not tried them in my TC50 yet, as I don't want to void my warranty. However, I have tried them in my Mark V, and I really enjoyed what those did for that amp. But, I have a matched sextet of 6CA7s on hand to try them when I am ready. I also got a pair of Gold Lion KT77s as another person here has said they are stellar in the TC50.