Bit out of topic.
I never tried SED valves, but in my PL Plologue Two, KT88 gives more body, like Newbee wrote, and I think this is what you may expect, generally speaking.
Personally, I compared NOS 6550 Tung Sols grey plates with holes, NOS 6550 Tung Sols Black smooth plates, NOS 6550 Sylvania and NOS GEC KT88, which I am using now. NOS 6550 Tung Sols Black smooth plated are great, but not as much as KT88, however may depend in which amp, or simply putted set up, you are using them.
The bad thing, as always with NOS, they are very expensive, but from what I heard/read, TungSols, even they are below their minimum, still sound wonderfull, talking about Black smooth plated from 50's, but they dont have that magic of GEC, I would say KT88 are more involving/musical as well, at least to my ears.
I never tried SED valves, but in my PL Plologue Two, KT88 gives more body, like Newbee wrote, and I think this is what you may expect, generally speaking.
Personally, I compared NOS 6550 Tung Sols grey plates with holes, NOS 6550 Tung Sols Black smooth plates, NOS 6550 Sylvania and NOS GEC KT88, which I am using now. NOS 6550 Tung Sols Black smooth plated are great, but not as much as KT88, however may depend in which amp, or simply putted set up, you are using them.
The bad thing, as always with NOS, they are very expensive, but from what I heard/read, TungSols, even they are below their minimum, still sound wonderfull, talking about Black smooth plated from 50's, but they dont have that magic of GEC, I would say KT88 are more involving/musical as well, at least to my ears.