For new production try Svetlana's (C logo's). Rugged and dependable. I've yet to have one fail prematurely.
How to pick which brand of 6550 tubes to purchase
I have a pair of Ray Lumley M-100 amps. Have used two complete sets GE 6550 for close to twenty years. Need new tubes. Which tubes would you recommend to purchase? Any knowledge of the sound character of the different models. I like the accurate/neutral type of sound versus the too valve sound.