I have never been a fan of 6550s but just replaced Svetlana KT88s with RAM - tested Sovtek 6550 WEs and am most pleased Sound like clear-tops to me. Take a listen if you are able.
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.