Hi Butler, my amps are probably from the early 90's and I use Ei 6CA7 power tubes (similar to EL34 but with better bass they say). I have tried 6550, KT90 and KT88 as well but I like the ones I use now. Besides, big tubes doesn't really fit. It's very tight between the tube sockets and the transformers. Jadis must have changed the layout of the amps a bit to be able to use KT150 tubes.
I have tried many different speakers and no matter what speakers I use some factors are the same. I have NOT tried speakers with very high sensitivity, that remains to try some day. Only from 84-89 db which can be very challenging for these tube amps I admit! I listen mostly to jazz and rock (blues based rock too) in a small apartment living room. There's no question about it that these amps are much better with smaller settings, 3-6 piece jazz groups, singer songwriters, soul vocalists, small ensemble classical music and well recorded rock, blues and country bands and albums preferably released before the "loudness war" era, if that makes sense? (Some modern records sounds really awful no matter what amps you use.) These amps are great and can sound really magical, the sound gets very very emotional and real if the parameters are right, trumpets, guitars, vocals etc. That's what Jadis is about I think.
The amps have worked very good with most speakers I've tried but the higher sensitivity and easy load the better, vintage speakers are great for instance. If you hear about speakers that are hard to drive they probably aren't a good match for these Jadis amps. Right now I'm using old small Tannoy Eaton's, it works lovely. I don't know if they work with electrostats. Are yours active in the bass? The bass is good on the Jadis JA30's if the music isn't too complex and if the speakers are not too "slow" in the bass from the beginning, but of course the amps can't be compared with high power solid state amps, it's just not possible and not really fare. The KT150 tubes are probably making the bass a lot better though, I'd love to hear that some day. If you are worried about if these amps are enough you might be better off with the Jadis JA80 power amps, the regular old version can probably be found much cheaper than new JA30 mkII's. I would look for those personally if I where you and worried about the power reserves, but I can't know for sure of course.
My amps have been working pretty much flawless so far during the years I've had them. And I love the looks, the feel, the sound, pride of ownership etc etc. Very cool amps. I also own an integrated Jadis Orchestra amp and it is lovely as well, I like the brand very much, definitely floats my musical boat. :-)
