Beemerrider, Not everything is equal. You cannot make such a broad assumption.
I think one of the reasons that folks like KT88's is that they serve up a warmer frequency response than other pentodes and are a better match for a lot of components which have been designed with emphasis on detail and resolutionion the forefront. They err, if at all, on the warm side of neutral.
I have an amp designed around the KT90 that I use with KT88's that sounds better and and has better lower bass than a KT88 designed amp I use. I also have a pair of mono's designed for KT90's that sound better than either of the former amps w/KT88's (or KT90's) using 6550's. Using the KT90's in any of these gives even better bass response than any of these other tubes, I just don't care for the mid-range and highs of the KT90's in those amps.
What I have found in my amps is that the KT88's give a warmer upper bass, not as tight, but very pleasant and a bit more air and warmth again in the upper mid-range/highs, where as the KT90s have very strong tight bass, cool mids, and I think up tilted highs, and the 6550's are more neutral than either and can produce some very clear highs with no exageration and no bass bloom either.
Anyway, thats just my amps, my ears etc. YMMV. FWIW.
I think one of the reasons that folks like KT88's is that they serve up a warmer frequency response than other pentodes and are a better match for a lot of components which have been designed with emphasis on detail and resolutionion the forefront. They err, if at all, on the warm side of neutral.
I have an amp designed around the KT90 that I use with KT88's that sounds better and and has better lower bass than a KT88 designed amp I use. I also have a pair of mono's designed for KT90's that sound better than either of the former amps w/KT88's (or KT90's) using 6550's. Using the KT90's in any of these gives even better bass response than any of these other tubes, I just don't care for the mid-range and highs of the KT90's in those amps.
What I have found in my amps is that the KT88's give a warmer upper bass, not as tight, but very pleasant and a bit more air and warmth again in the upper mid-range/highs, where as the KT90s have very strong tight bass, cool mids, and I think up tilted highs, and the 6550's are more neutral than either and can produce some very clear highs with no exageration and no bass bloom either.
Anyway, thats just my amps, my ears etc. YMMV. FWIW.