time to discuss kt-88's

I have a suggestion of another avenue. I have tried Sovtek, Svetlana, JJ, and other KT-88's in the past in my Sonic Frontiers SFS-80. I mention this due to it using a pair of output tubes per channel as well. I was constantly tube rolling and was talking with Kevin @ Upscale Audio and he suggested I try Ei KT-90 type III tubes. He also warned the drawback of taking 400 hours to burn in and fully open up. Well, after tracking hours and about 385 hours into play time on the new tubes I was ready to give up. The mids were a bit analytical and not as open, the bass prowess was much better than any KT-88 I had tried, and the top end was clean and extended. Yet without the mids being open and relaxed, why have a tube amp? Uncannily a few days later while in the office, I got off the phone and noticed the piano (George Winston) sounded THERE... and I was down the hall a few rooms. I kid you not - 412 hours logged and there was a transformation! The sound was what I was searching for over many, many tubes. Overall, the bass was the most controlled and defined, the mids were open, airy, hamonically correct, with clean & extended highs. They were the most neutral of the lot and the least colored. The Ei KT-90 type III's also produced the best macro and micro dynamics.

I will mention the midrange was best with NOS GEC (Genalex) KT-88's from 1966... however quite expensive and a bit colored, with sloppier bass and highs a bit rolled off.

Currently I ordered my Quicksilver V4's with the Ei KT-90's from my experiences in the past. I haven't questioned my power tube choice once.

Some find the KT-90 to be more "analytical" sounding (and THEY ARE for the first 400 hours or so) but after that it seems to be extremely neutral. I tend to prefer to use NOS Mullards in the preamp, or a tube that is slightly warmer to "tune" the overall sound to your preference. That way you get the best control of bass, dynamics and a neutral power tube, and can tube roll relatively inexpensive on the preamp tubes.

You may want to make a call to Upscale Audio and get their advice on KT-88 / KT-90 comparison.

Good luck on your search!

Hey Basement - you can also verify with Kevin @ Upscale Audio, but I do think I was told 400+ hours on the KT-90's... and that is not the easiest amount of time to log on tube amps! However, when you do reach that point over 400 hours, you will know it. It was not a subtle difference. The somewhat "closed in soundstage" will also tend to open up as well. It may not be the best in the regards, but much more open as compared to when they are new. The mids and highs remain neutral, however seemingly silky smooth & clean. The bass will seem to have more "punch" and refinement as well when you cross the break in thresh hold.

Please keep us posted. Good luck!

Kevziek- I tend to agree with you with just about any tube... a good 15 to 40 hours and they are good to go. The Ei KT-90 Type III is the ONLY exception I have had in over a decade of tube rolling. I thought I was being fed a line when I was told 400 hours, and like I posted above I was ready to throw the tubes out at about 380 hours. However, with the money invested and the time, I pushed on past 400+. Let me state again, the transformation was NOT subtle. THE transformation appeared about 410 hours or so... everything improved, and when using electrostats it was very clear what changed, air, openness, transparency, transients, etc.

Again, I too would agree that this sounds totally crazy and would think it is nothing but bull$hit, until of course I went through it myself...

Kevziek - If I am not mistaken, many would argue the KT-90's are built like a tank and I believe I have been told their useful life is 4-6K hours if biased normally. In my past experience I had well over 4,000 hours on my set and the tubes were showing no signs of wear. On my current set with my new amps they are just shy of 400 hours... :)

Kevziek -

I have also heard horror stories on early production runs on the Ei KT-90's. I can not comment as to the type I and the type II's as I have only had experience with type III's. Here is a link to show you the visible differences:

http://www.manleylabs.com/galleria/KT90.html

I have also owned a matched octet of the EI "fat bottle" EL34's many years ago (about 6 or 7) in Cary SLM-100's. I did not prefer the sound of the amps and only kept them a few months, but have never had problems personally with any of the Ei tubes yet.

However, even good tubes go bad, as I once had a Sovtek KT-88 blow and take out the left channel of my Sonic Frontiers SFS-80 in the past.