tube amps and electrostatics

You forgot to mention Dhcod that they also dive down to below 2ohms as well. And don't go by the Stax published impedance graph, it's fudged quite a bit, we measured it and it's far from what they pictured. Add to that it's capacitive loads and you have a speaker that is easy to drive at some frequencies and a down right pig at other frequencies.
And a quad esl 57 is even worse. And other ESL's are just as bad if not worse again, look at the Martin Logan Montise crazy amp impedance load and add to that the nasty phase angle, amps with current need only to apply.

http://www.avsforum.com/t/1454033/amp-for-electrostatic-speakers post number 12

http://www.stereophile.com/content/martinlogan-montis-loudspeaker-measurements

For over 40 years I've only used ESL's
Quads, RTR's, ML, Acustat, Stax. Sure some of my big tube amps will sound good into them, but nothing drives them like a strong current bjt output stable solid state can. Direct drive esl's can also sound good but that's getting into the deadly territory

Cheers George

Mr G- You may want to realign your blanket statement, re:
MOS-FETs
and
current. MOS-FETs are innately self-protecting, regarding
thermal
runaway, unlike bi-polar transistors
(http://www.onsemi.com/pub_link/Collateral/AND8199-D.PDF).
I sold(mostly modded)
David
Hafler products, for years, which all used MOS-FETs as
output
devices. As a sales point: I used to demo the DH-500,
measuring the amperage into a 2 ohm dummy load. I had read
as
high as 48 amps, without damage or overheating(and thermal
protection activation). You could practically arc weld with
the suckers! I, as well as a couple other customers, owned
Acoustat Model III's, and had excellent results with the
Hafler amps, at realistic SPLs.

Sorry but Mosfets can't do current like BJT's can. They can do watts no problem though.
Show me published specs on a Mosfet amp that can almost double it's "tested" watts output all the way from 8 to 4 to 2ohms and I'll show you a case for legal action.

Cheers George

George and Ralph, not really interesting in starting another discussion on the differences between Voltage Paradigm amps (generally solid state amps with very low output impedances -- high power SS amps can generate high current) and Power Paradigm amps (usually tube amps with higher output impedances).

Suffice to say that as Ralph and Al (Almarg) have said many times, if a speaker was designed and voiced to be driven by a Voltage Paradigm/SS amp, using a high output impedance Power Paradigm/tube amp will likely result in acoustic colorations. The reverse case also being true.

But hey, not all acoustic colorations necessarily sound bad. ;-)

MR G- I can't recall ever seeing anyone publish specs,
claiming to double output wattage, all the way to two ohms.
Nor did I claim that for the amps that I sold. re: Current
handling/MOS-FETs
vs BJTs: Maybe that first article wasn't clear enough, or too
technical. Here's something a bit easier to digest, perhaps:
(http://www.ixys.com/Documents/AppNotes/IXAN0061.pdf)