I don't know if they are still in business, but check out Coastline. They made big powerful tube amps. There is also Tube Research Labs.
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While superb in build quality and sound, almost all Atma-sphere amps are output-transformerless and are thus intended to be paired with benign impedance loads - I do not know what the above poster was thinking.
The easy answer to your question is any of the CAT monoblocks. They have the best output transformers and stiffest power supplies of any tube amp I am aware of. They were designed to drive the mbl 101E, which is 83 db. efficient and features outrageously tough impedances. The original version, the JL-1, was all point-to-point wired and massively overbuilt, especially the $50,000 JL-1 Limited Edition version, which had crazy parts quality. Rated at only 100 watts per channel, they sounded like a 500 wpc Krell and could probably power an arc welder. Each monoblock weighed 192 lbs., 55 lbs. of which was the outrageous output transformers. The later version, the JL-3, uses circuit boards, as does the stereo version, the JL-2, but they are still great amps.
There have only been a small handful of regular production tube amps that have output transformers and power supplies of the quality required to properly drive low impedance loud speakers: the above described CAT's, the Air Tight Reference monoblocks (also $50,000), and some of the Audio Valve amps are in this rarefied category. The VAC Renaissance 140/140's also have excellent output transformers and can drive very low impedance speakers. Sound by Singer in Manhattan was unable to drive the big Pipedreams with the VTL MB 750 mono's, but had no trouble driving that speaker with the 65 watt/channel VAC Renaissance 70/70. The issue is not watts per channel, but the quality of the transformers and power supplies. The VAC Renaissance, the CAT's, the Air Tights and the Audio Valves are all point-to-point hand-wired, incidentally.
Putting aside whether they can drive low-impedance speakers, my personal opinion is that the vast majority of high-powered tube amps (and high-powered solid-state amps, come to think of it) sound like shit because they require some degree of negative feedback to control to circuit. With all of those tubes, they also require too much TLC and tend to heat up listening rooms. The safer and easier route is very high-quality solid-state, like the darTZeel, which can drive low impedances, yet retains ease of ownership and superior sound quality.
I think this is what you're looking for:
but that said, I'm wondering why you think you need so much horsepower to drive Sashas?
I also want to mention, that if you were driving your Quads through Cardas Golden Reference speaker cable, then the Quads didn't stand a chance of delivering truly great electrostatic performance, because electrostats need to be driven with very low capacitance speaker cable; less than 20pF (picofarads) per lineal foot. And if you'll go to the Cardas website and look up the specs for his Golden Reference speaker cable, you will discover it's capacitance is a whopping 216pF per lin.ft. -- about ten times what an electrostat should be looking at. Electrodynamic drivers (cones, domes, and ribbons) would prefer low inductance. And if you are using a tube amp (with output transformers) additional inductance in the speaker cable can (negatively) affect the amp's damping capability and thus its ability to produce really clean bass, no matter how much power it has.
Thanks everyone for your answers and suggestions! I think there is some very good wisdom in many of your responses and you got me thinking that I need to be more concerned with current versus watts. I wish I could afford some of the rarefied suggestions but they are just out of the question for now.
THE question of the thread is of course, "Why do you think you need a tube amp?" Great question and the answer is that nothing is wrong with what I have now, but I'm just looking for some variety to switch things up.