time to discuss kt-88's

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:

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.