Ok returning back to the KT90EH...
I recieved them a few days ago. So far they have maybe 15 hours on them.
I would like to restate that i'm very new to the tube sound. So I hope this opinion will be useful to someone.
Current system is a rebuilt ST-70 using the VTA driver with 6SN7 tubes. Also i've opted for a new power tranny. Picture is the third down on http://www.tubes4hifi.com/ST70.htm main page thx Roy. I'm running all custom speakers and custom crossovers. Dayton Audio RS125-4 x 2 and Tang Band 28-847SD per cab. Listening source varies. Pro-ject turntable and digital sources.
Currently I have them biased to 50ma. I believe my bottle neck for power is the stock ST-70 OPT's. That being said the system provides plenty of power for my needs.
If you haven't seen a comparison check out the pic below. Although the tube glass is roughly the same size the tube elements are much larger. You can see the base is very low profile. I kinda wish it was a little more substantial. At first glance they are not as different looking to the old KT77's as a KT88 or fat glass tube would be. So.. they are larger but not as impressive looking than a KT88 would be I guess.
At first power up I noticed the highs being a bit soft and the bass was over emphasized. I came across a post with a similar experience so I don't feel alone in this. They have leveled out but there are still very new. Right now they don't sound terrible. The bass is still a bit heavy but not all together unpleasant. Once I get more time on them I will try to give a more detailed impression. Right now i'm on the fence.
Just got the Gardians Of The Galaxy LP. Its not sounding to bad right now.
These observations are in relation to the EL34 and KT77 tubes I was running previous. Also my complete lack of exposure to any other tube amplifiers. I preferred the sound of the KT77 over the 34's so the 34's were shelved quickly after I got them. I will have to try the 34's again to see if my opinion stands.