time to discuss kt-88's

It is time to retube. I have quicksilver 90's, and I understand different amps like, or may like, different tubes. I have searched the archives and found little discussion on kt-88 types. I have also wacthed a few post go through without a responce on different amps seeking advice on which tube that use kt-88's.
There are more options for kt-88's lately from svetlana, sovtek, jj and electro-harmonix. I feel that we, as audiogonners, should be discussing them. What are your opinions of these different tubes? What are the differences between them, how do they compare to n.o.s.? Any great bargains or sleepers? ect.
i own the harmonix in my aes dennis had signature amp and they are fast, and good on bottom end.....
I have used Svetlana and Sovtek KT88's but haven't tried the others yet. I found the Svetlana very clean and clear in the upper mids and highs (very impressively so) but a little thin in the bass and lower mid range. This was in a SF amp. I tried the Sovtek's in the same amp and was unimpressed until I changed the small tubes from Teslas to EI6dj8's - this brought the Sovteks to life and they have been in the amp in this combination for over a year now. I'm encouraged to try the EH's .......

I did not have such luck with the Svet KT88's regardless of the small tubes. I presently use Svet 6550s & JJ 6922's in my SF mono's which gives me a very balanced and detailed sound w/o excessive high end energy. Caveat - I focus on rugged tubes in my amps and have avoided some of the popular, but less reliable stuff. I hate lugging these beasts in for repairs because of a blown tube.
I recently traded my JJ KT 88s from my Audio Aero Capitole amp into my McIntosh 2102 amp just to see what would happen. the Svetlana Kt 88s made an amazing improvement to the Audio Aero. so much so that only now do I realize just how wonderful this amp sounds. I got on line and bought another set of Svetlana KT 88s to put back into my McIntosh. While I was at it I changed out most of the rest of the tubes in my system.

Anyway, you will find lots of support for the Svetlana KT 88 tube and perhaps even more support for electro harmonix which I have not yet tried.
I really like my Electro Harmonix KT-88EH in my ARC VT-50. The bloom I enjoy without the slight dryness of 6550. Just my 2 cents.
I'm also running EH KT88s, 16 of them, on my ASL Hurricane monoblocks. A worthy upgrade to the stock tubes!
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!
Thanks, guys. I'm still surprised there isn't more folks here who want to discuss kt-88's.
The first time I tried the silver 90's was a short trial, and they had svetlanas. I remember the sound as being REALLY clear and smooth in the midrange, but soft in the bass and lacking the deepest bass completely, and vary soft on top. While I was really unsatisfied with these shortcomings, the mid was so beautiful that I proclaimed "these amps could actually get a guy laid".
The silver 90's I have now came with kt-90's, and I did not like them at all. They also came with cv378 rectifiers. I soon replaced them with chinese kt-88's and then was pleased, as the highs came back I was lacking with the kt90's, and the sound opened up the way I knew it should. I then replaced the rectifiers to the 5ar4's it called for and the sound became tighter and punchier. Did not seem to have the mid range clarity I remembered with the first pair though.
I got on the web with upscale audio, (that is where the tubes were sourced), and to my surprise they had this 'cv378' rectifier where it explaines you may "lose highs and lows", along with some plate voltage warnings. I put the kt90's back in (with the 5ar4's) and no longer do they have the severe lack of highs and definition they had before. In fact, they seem to have very good definition. They are very detailed, have good presence and 'punch', and great bass. they are, however, real flat in dimension and not very open sounding.
I thought that perhaps they were starting to burn in some when I read audiofankj's post. They are starting to sound a lot better, some 30 hrs later. I think I maybe played them for 150 to 300 hours when I got the amps, and I don't know how long before I got them, so I will continue to let them cook. I might be living on the edge, though, as it seems the reason for the cv378 rectifiers was to lower the plate voltages so the amps could handle them. The amps call for 100ma with kt-88, but with kt-90's, the plates on one of the tubes in each pair glow just a LITTLE in the crease, so I have them at 90ma to minimize this.
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!
Tubes taking 400 hrs. to burn in? That is completely ridiculous. Electrons traveling in a vacuum don't "burn in." If you argue that cathode & anode burn in, that is going to happen within a few minutes from new. You're probably just getting use to the sound of the tubes, or they are changing in sound because they have already aged in 400 hours.

As far as comparing KT-88s, this will differ from amp to amp. You need to get recommendations from Quicksilver owners, or from Quicksilver themselves. In the ARC VT-100 Mk II, I found the Svetlana to have a beguiling sound with some pleasant 'tube fog' in the midrange. Decent, but not outstanding bass, silky treble that does not have the ultimate in detail however. The EH KT-88 is a very good tube, as is the JJ KT-88. I would try those in the Quicksilvers, as Quicksilvers have had a reputation for a very midrangy, bloomy sound that could use some bass tightening and high end extension.
Yes, 400 hrs for a tube to burn in IS rediculas, but I have experienced rediculasly long burn in periods in other areas.
I did call upscale to ask about this, and they more or less confirmed this, saying about 300 hrs, and that they have an "unusally" long burn in.
My assesment of the svetlanas is not nessesarily different, but in the quicks, what I heard was definitely a very 'clear' midrange, in fact, was able to pick up a lot of the harsh, buzziness that a real trumpet or saxaphone sounds like. Synergy is sometimes matching strenghts and weaknesses, and sometimes it is just a unique situation. It is worthwhile to note or discuss what tubes work well in what amp, and of coarse while assesing a tube the amp it is in must be considered, but there are still differences in tubes and brands that make them stand out or just be so-so. It is interesting that the svetlana, that seems to have such a glorious midrange and soft and soggy highs and lows would not balance out in an arc, but this could be telling, too.
The kt-90's ARE changing to me, which I will comment on later, and I should also note that in my experience, the quicksilvers to me are not amps that have long burn in periods with different tubes or long warm-up times.
I will continue to burn these tubes in and report back soon.
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...
I wouldn't want to have tubes that take over 400 hours to burn. Based on an estimated useful life of 1,500 hrs., 1/3 of the tubes' useful life will be gone before it is burned in.
Yea, I'm burning the hell out of these kt90's. I have logged about 70 hrs since fri. I have left them on non-stop except for about 3 hrs today to let them cool, and recheck the bias as I fired them back up, so I could kinda keep my eye on things. (btw, yea, 400 hrs IS a pain in the butt, but then again, this is fun).
So, I have to report, because these are turning into some nice tubes for me. They ARE changing, and a lot of what I am hearing is pretty accurate to audiofankj's description.
Now, first off, it is true that getting used to, or accustomed to, is relevant. It is also relevant to have such a detailed description of what to look for, while it may seem that I am being swayed by such, I am LISTENING and I am sure of what I am hearing. (extraordinary claims should require extraordinary proof).
The bass has really opened up, and goes deeper than I have ever heard through these amps. But more important, it is very 3-d AND solid. The bass sounded tight before, but what has really changed is that there is much more detail in this regard, both in the staging qualities and the perception that there is now a lot more information being reproduced.
The treble, while I could desribe as less hashy, really hasn't changed changed in overall timbre or character except to say that it appears to be having the same effect as the bass-that is, there seems to be more separation between different treble frequencies.
What is really different about the sound of these tubes from what they sounded like before as they burn in is in the detail, like they have suddenly and astonishingly became able to resolve textures and harmonics that they could not before. While perhaps the staging qualities may be the same, the extra detail with the instruments is giving space to them, and one thing that is definitely different is that now, an individual note or voice now has a depth, and is reproduced with an individual dimension, where before it was flat, which helps with the effect that the staging is better overall. It also seems that the bass, and the fact that it definitely has MUCH more dimension and definition, is integrating to really give the midrange realism.
What really seems noteworthy to me is the way these tubes focus, as the sounds that are coming out of my humble vandy 2ci's is really pinpoint, And the images are definitly 'there'. What is presented by the speakers has a very solid place in the room. Each instrument or voice sounds like it is at a very specific place that is easy to make out. While the chinese kt-88's presented everything wider and deeper, With greater separtion between sounds, The greater detail of the kt-90s and the 'precision' of the effect has its own effect on the overall picture.
That's all for now, as I feel I am struggling to describe this. In short, what I am definitly hearing is a lot more detail coming from these tubes now, and it is having an effect on the meaning, the impact, on what these tubes sound like.
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... :)
I have heard claims about how long a tube is supposed to last before. When I had small signal EI tubes (EL84) their construction appeared very cheap and unimpressive. The glass was thin, the pins were flimsy. Overall, they did not inspire confidence. Actually, I remember replacing them with EH tubes, and the sound was far better. I know we're talking about KT90s, not EL84. However, I would expect that if the construction and reliability were not good on other EI tubes, these would be questionable. I remember many criticisms of EI-90's blowing up amps. In fact, I owned an amp that the prior owner had to repair because of failing EI KT-90s. I hope you are right, and these present production KT-90s are in another league.
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:


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.
I talked to Mike Sanders today. I wanted to get his recommendations for kt-88's as well as discuss the viability of kt-90's in the silver 90's. (Quicksilver makes a currant model that is very close to the silver 90's, the mono 100's, and he offers them with kt-88's or kt-90's, but does not list kt-90's as replacements for the silver 90's).
As I mentioned before, there is some glowing of the plates, so I initially ran them at 80 or 90 ma to minimize this, as opposed to the 100 ma specified for the silver 90's. It made me wonder if the silver 90's could handle the kt-90. Mr. sanders said the silver 90's are fine with the kt-90 tube. I told him about the glowing plates and he said that is a tendency, but he wonders about it himself. He runs the kt-90's in the mono 100's at 80 ma, but some dealers run them as high as 120 ma.
I also discussed with him the slightly varying bias currents I was experiencing. When I first installed the kt-90's again, it took some 2-3 hours before the bias would settle, it would not jump quickly, but it would be at say 95 ma, and over the course of time, drop to say, 85 or 90. Now, some time later of break in, it takes about 20 to 30 minites and starts off with what seems like 4-6 ma higher than what I adjusted them to before settling back. Mr. Sanders attributes this to the power draw of my conditioner, or my house, but I wonder if it is related to the plates, or both.
Anyway, I can attest to the LONG break in of the kt-90. Perhaps this is due to the unusually robust nature of this tube that seems to be what I am hearing about them. I am also aware of tubes that are more robust than the standard that do glow in the plates, although for most tubes this would be bad, and evan if they didn't fail would wear quickly. I do not know if this is a tube with a tendency to glow in the plates when used within its specs, or how long it will last operated like this, but if I adjust the bias in the silver 90's to where they don't glow at all, I get audible crossover distortion, and I like them best presently at about 95-102 ma, so that is where I have been running them and everything I have said about them has been at this setting.
I thought this may be interesting to you guys as it relates to the reliability, and maybe the break-in as well.
To stay on thread, I have really liked the Svetlana kt-88s but had some reliability problems running them in Audio Valve Challenger amps. Recently I came across some RAM-tested kt-88s that I now prefer.

Regarding kt-90s I find the assertion that they require very long burn-ins to be interesting. When I rolled them into various amps, usually replacing 6550s or kt-88s, I only let them burn in for 40-50 hours before determining that I did not like them. Who knew 400 was the ticket?

My current tube reference amp, the Jadis JA-100 uses 4 kt-90s per side and it sounded great right out of the box. It improved over the first 60-70 hours and then settled in. The improvement was noticeable but not dramatic. Jadis assures me that the tubes were new. They say that the kt-90 places special demands on the power transformer so they developed a proprietary hand wound unit specifically designed for the kt-90 tube. The amp self-biases and the tubes do not glow bright in the plates. I am not an expert in this area but I do trust Jadis to know a few things about tubes. Maybe it takes 400 hours for kt-90s to burn in a standard transformer?
One thing I don't see discussed much, except in this posting is the compatabity issue. Bias voltage, and plate voltage seem to be different for this tube, and they don't seem to be a drop in substitution for Kt88s, or 6550, if all paramaters are not met, resulting in plate glowing, short live, etc. Has Any one used them in dynaco mark IIIs, what luck, and what mods were made to accomodate them, from bias, to plate voltage? Check out the Citation page on the web to see comments about bias, and voltage, which makes me post this, as I need to retube, and am unsure of going with the EH Kt88, or the EI Kt90. Then of course there is the Kt 100 which we don't seem to hear much about.

Any suggestions?
Issue #19 of Vacuum Tube Valley did comprehensive listening test with current production and NOS KT-88 and 6550 tubes. You should check it out.