time to discuss kt-88's

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.

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.

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.

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.