tube amp dilemma with electrostats

Hmm...I'm not much for 'warm', because that turns into 'thick' VERY quickly for me, but I do prefer a little warmth to absolute tonal neutrality. I suggest a used conrad-johnson Premier Eleven-A. It's rated at 70 Watts per channel into 2, 4, 8, or 16 Ohms. Again, if the Mac 275 had enough power, the Eleven, too, will. Elevens are available for c. $1500 here. I just sold my 2nd or you could buy mine for $1450.

If the Eleven doesn't have quite enough power, you could buy a pair of Twelves ('the same' amp but single channel for 140 Watts into 2, 4, 8, or 16) or merely buy another Eleven and run both in mono. The Twelves show up here occasionally; the Elevens often.

If you have more money than I to spend on this stuff, buy a new Premier 140, which is a current-generation 140WPC stereo amp that EVERYONE loves.

WOW there's one right here--http://cls.audiogon.com/cgi-bin/cls.pl?ampstube&1113954455 . If $4700 is a little much, and BOY do I wish I had it, there's also a pair of Twelves here now--http://cls.audiogon.com/cgi-bin/cls.pl?ampstube&1114028794 , for a few-hundred$ less. Personally, I'd buy the Twelves because I LOVE monoamps, but if you have no unnatural attraction to single-channel amps, the 140 is the better buy, IMO of course.
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I forgot to say earlier that I'm driving a pair of Quad 989s with New Generation-brand 100-Watt tubed monoamps, switched to triode--see my System here. They have maybe 40 Watts in triode, and that's plenty for my fairly large room and my listening preferences.

Good luck in your quest.
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Well here's a thought for you. When you listen to an amp you are listening to a lot more than the power tube. An amp with 6550's can sound bright, dull, or quite nice and a lot depends on the driver tubes.

Years ago I got a Sonic Frontiers SFS80 and I didn't care for the sound of it with 5 different brands of 6550's including Svets - I was using Siemans and 6h23EB drivers. Just to much high frequency energy. I found it sounded quite plesant with Svetlana EL34's but I gave up half of its power. Page 2...

I got a pair of SFM Mono's (160wt's) they came with Svet 6550's and some Sovteks - didn't care for the sound, but this time I changed out the 6922's and replaced them with some EI's. Great result from such a minor change. All off the highs are still there but now they are clear as the proverbial bell, no undue emphasis or energy anylonger in the upper mids/highs. Page 3.....

I went back to the SFS 80, put in Svet 6550's and EI 6DJ8 tubes and I now have a great back up to the 160's. The SFS 80 is only a tad warmer.

Moral of the story, if you haven't got it by now - those small tubes make a huge difference. IMHO, as much or more than the power tubes everyone talks about. So experiment with them before you reach any conclusions about what an amp (can) sounds like. It ain't about how big it is, its what you do with it that counts. :-)

FWIW I've driven my Quad 63's with both of these amps. The results of my rolling these tubes is as apparent (and appealing) on these as on my dynamic speakers.

While I normally dislike making amp recommendations for specific speakers I haven't owned, I would say that I've seen both of the SF amps I mentioned selling for 1000 to 1500 respectively on A-Gon. FWIW

I would give a second strong recommendation for the ARC VT100.