I ordered a quad of EH KT90 vacuum tubes from Jim McShane a couple of days ago to try in my Leben CS660P stereo amplifier. I was thinking that I'd tried KT66, KT88, EL34, KT77, 6L6G, 5881, 6n3cE, 350B, and 6550s, so I thought I'd better add KT90s to the list. My favorites so far have been the 350B and the 6n3cE (in the photo below, left).

I was impressed with the tonal signature of the KT90 when my friend Ron brought over his vintage Harmon-Kardon Citation II amplifier that he was using  KT90 tubes in. The KT90 tubes had a big, warm sound, that kind of reminded me of an EL34 on steroids. The more I thought about that, I thought it might be a good match for the CS660P. Today the KT90s arrived, I plugged them into the Leben CS660P, and let it warm a bit. I put on the Analogue Productions 45 RPM version of John Coltrane's Blue Train and gave it a listen. My first impressions were very positive: warm, with a lot of timbral textures, and deeply infused tonal colors. They're brand new out of the box, so I'll post an update after I get some hours on the tubes and they get into their full stride. In my brief audition I'm finding I like the voltage switch set to 410 volts (switch down, indicator light green).

Update: Tonight I tried the EH KT 90 tubes in my Leben CS600 integrated amp. I have to say, the KT90 is an extremely likeable vacuum tube, it has a warmth and body to it that will delight a lot of listeners, particularly those that have speakers that tend towards being a little bright. Even with my Harbeth SHL5s I have to say the KT90 is pretty magical. Is it better than the 6n3cEs with the SHL5s? The verdict is still out. But the KT90 is enchanting, and whatever you're running right now, I suggest you give them a try and see what you think. Be forewarned, if you decide to try them in your CS600, you will need to leave the top cover off, as the height of the KT90s exceeds its limits. Oh how I wish there was an optional Leben top cover that accommodated the more masculine tubes!

Thanks for stopping by, and I'll report back what the results are when I get a little more time in on them.

Best,

Jeff