tube amps and electrostatics

And what you would have also heard was a more defined and extended treble because those quads and these (ML's Acustats and other els's) go below 1ohm in the treble and start that impedance dip at 10khz.
Tubes I aggree with these speakers still sound good but they are definately subdued in the treble compared to a GOOD s/s amp that is BJT output and that can do current into low impedances. Like you found with the ML2 which can almost keep doubling it's current down to 1ohm for each halving of impedance.

This is not entirely true. Quads and Soundlabs have a higher impedance at 20KHz. In the case of the ESL57 and ESL63, the 20KHz impedance is high enough that even our small M-60 (60-watt OTL) can drive the speaker easily with no loss of HF performance.

In the case of ML, later Quads and Sanders ESLs, because the manufacturer is wanting to open up their market to more transistor amps, the impedance is quite low at 20KHz (some MLs are only 0.5 ohm).

In cases like these, you do as Tomcy6 mentions- you get a set of ZEROs (http://www.zeroimpedance .com) which allow you to easily drive ML or whatever! We have several customers doing just that with our older MA-1s (12-tube version) that only make 100 watts/channel, and they have no problem whatsoever making high frequencies on the speaker, with proper response to 20KHz and beyond.

12-04-13: Frogman
OK, George, you win; clearly, I don't know what live music sounds like.

Hopefully Frogman won't mind if I provide some perspective on his comment by stating what he is too modest to say, that he is an accomplished professional musician in the classical, jazz, and other genres.

Regards,
-- Al

Just the Quad ESL57 impedance curve, my ML's and Acousats are even worse when I measured their impedances.
http://www.quadesl.com/quad_main.html
and add to this the highly capacitive nature of ESL's, and you can see why Roger Sander says Solid State is better than Tube or OTL Tube for ESL's

The only tube amp which is great match and is not worried by these impedance drops is High Volatge direct drive tube amps (up to 5000v at the speaker terminals). For ESL's like the oringinal Acoustat X. But these are difficult and hard and make safe. As you can imagine.

Cheers George

There's no question that when driving the many ESL's that have impedances descending from high values at low frequencies to very low values at upper treble frequencies nearly all solid state amps will provide an increased emphasis of the upper treble in comparison to nearly all tube amps (assuming the amps being compared are operated within the limits of their voltage, current, power, and thermal capabilities).

Which of those two kinds of amplifier/speaker interactions results in the most correct acoustic output from the speaker is a separate question, however.

Regards,
-- Al

I think Al got it right again, as usual. :-)