I have used EI KT-90 Type III tubes many times as well as Svetlana & Sovtek KT-88's and both of their 6550's...
The Ei KT-90 type iii (make sure to get the type 3 - the earlier versions were more 'zippy') will produce more power than a KT-88. The bass will be better controlled and overall it will be a more linear tube. In my situation with a few different amps, it took my KT-90s about 400 hours of play time before they had the "effortless" presentation to them... they sound decent at first, but there is a bit of "strain" or congestion until they do burn in a bit. I can not explain why this seems to be. It was advised I log the hours on the new tubes years ago upon insertion and that is what I found, as well as two times since then. I don't personally find the KT-90 to be "solid state" at all after the 400 or so hours of break in. The midrange is liquid and harmonics and timbre are natural.
I do love the midrange presentation I have heard with NOS Genalex KT88 as well as the Svetlana's... however in my instances, the bass was not controlled the way I would like it to be.
Good luck on your journey. This is the joy of tubes... you will prefer one or the other!
The Ei KT-90 type iii (make sure to get the type 3 - the earlier versions were more 'zippy') will produce more power than a KT-88. The bass will be better controlled and overall it will be a more linear tube. In my situation with a few different amps, it took my KT-90s about 400 hours of play time before they had the "effortless" presentation to them... they sound decent at first, but there is a bit of "strain" or congestion until they do burn in a bit. I can not explain why this seems to be. It was advised I log the hours on the new tubes years ago upon insertion and that is what I found, as well as two times since then. I don't personally find the KT-90 to be "solid state" at all after the 400 or so hours of break in. The midrange is liquid and harmonics and timbre are natural.
I do love the midrange presentation I have heard with NOS Genalex KT88 as well as the Svetlana's... however in my instances, the bass was not controlled the way I would like it to be.
Good luck on your journey. This is the joy of tubes... you will prefer one or the other!