Jaq , Your concern over JJ is realistic but a maddening tradeoff because they do have the best tonal qualities of any current KT88.Both JJs I bought from a well known Canadian tube dealer went bad frying 2 different ASL amps--- expensive repairs both times.The word from a previous thread about this stated that KT88s are the most easily damaged tubes and do poorly in shipping. Try finding a vintage amp that uses 7591 power tubes. This is great tube sound.
6550 to KT88
I switched out my EH6550's to JJ KT88's yesterday in my Rogue M120's, quite a difference from the get go...much better bass, sound stage is wide/deeper and overall I like the way they reproduce the music better... so now I'm wondering if the KT90's will be any better? Anyone go from the 88's to the 90's and stay with the 90's? Thanks for your comments.