Using tube amp with electrostatic speakers.

Bag, The ORIGINAL ML CLS was a match made in heaven for a tube amplifier; it was a nominal 16-ohm load.  After I auditioned a pair in a store, I bought them immediately and loved them in my home system, although they were a bit bass shy.  I related this same story somewhere else earlier in this thread.  Very shortly after the CLS debut, ML could not leave well enough alone; they rapidly replaced the original with the "CLS II".  This is the speaker to which you refer when you speak of difficult to drive. Foolishly, I replaced my CLSs with CLS IIs without knowing much about the difference between them. Turns out, the II had a hellacious impedance dip at mid-frequencies, as you say, I think down to 2 ohms at something like 1-2 kHz. This was bad for any amplifier, and it sounded awful with my then Futterman OTL tube amplifiers.  ML got the message very quickly and replaced the II with the IIz, which was merely a bandaid on the problem they introduced when they went from the original CLS to the CLS II.  To my ears, the IIz bore no comparison to the original CLS in greatness. At that point in time (when the II was replaced by the IIz), I called the factory and asked them what was up.  They told me quite frankly that they did not care much that I could not drive the CLS II or even the IIz with my OTL tube amp; they were playing to the SS amplifier owners.  If you like the IIz with a tube amp, look around for a pair of original CLSs; they are Quad 57-like in their midrange transparency, only with more oomph.  Way better than any version of the CLS that came after them.

All flat-panel ESLs (and magneplanars too) will have issues with beaming, increasingly at treble frequencies.  I am not sure that the ML curve or the SL pseudo curve completely cures this problem.  If you love ESLs, you live with it.  I also don't think that the curvilinear design of the ML speakers is a "real" issue in causing audible distortion.  It's a theoretically real issue that a competing manufacturer, like Sanders, can use in advertising.  The original CLS was one of the lowest distortion speakers I have ever heard in my life.

I heard the Sanders amplifier (not his speakers) extensively driving my friend's large Acoustat speakers.  He and I were very underwhelmed, despite all the bloviating about voltage.  He sold the amplifier within a few months and replaced it with a Berning ZH270, a pair of them, in fact.

Ralph, It's amazing how you keep such a cool head and give such great responses.  How many thousands of times have you done this?

I hereby nominate you to the Audiogon Pantheon/Hall of Fame.

Having owned every kind of magnetic - Maggie type, ribbon ,ML, and 
Sound labs. The size also of the panel has a lot to do with demands.
by far these panels are far better controlled with the High Current of a Solid State
Amplifier, where Vacuum tubes are Voltage driven .Current is what you need 
to get ultimate control ,with a Vacuum tube preamp  you can still have the sonic signature  you want. I have used 100wpc tube smps with them but dynamics suffer say compared to a Pass labs 350 power amp.

Arrrggghhh.  Audioman, please read the earlier posts in this thread.  You're preaching a certain kind of gospel put out by false industry prophets, but you're not speaking the truth.  Think for yourself and do some reading, and most of all know that (1) Magnepans and ribbons are entirely different electrically from ESLs and therefore should not be lumped with them, and (2) NO amplifier can "control" an ESL, because ESLs, not being electromagnetic in nature, do not produce a "back EMF".   Back EMF is the phenomenon best dealt with by an amplifier of any kind that has a low output impedance relative to the input impedance of the speaker at the frequencies in question.  This does not necessarily mean that only SS amplifiers need apply to "control" the bass response of an EM speaker; the output impedance need not be so infinitesimal as that uniquely afforded by an SS amplifier; tube amps with low output Z can do it as well or even better.  You might know this as damping or "damping factor".  Neither term applies at all to an ESL. 

If you want to argue that you prefer SS amplifiers to drive whatever planar speakers you own, that is fine.  Nobody's perfect.

I'm not here to denigrate or deny anyone else's tastes or findings.

Firstly, I never owned any versons before the IIz, and only heard a friends I many times as he sought to find an amp to drive them - Jadis, ARC, Krell, yada yada - he sold them.  The Scintilla's are the only speaker that was harder to drive and that's my experience in my 45 years in the hobby. 

There are tube amps that can handle CLS IIz's but they are either very expensive, or they are hybrids (as of about 2004).  I have never heard any tube amp under $15k that does justice to the bass - IMO.  Now it's been a long time since I've had them, and the state of the art has obviously moved ahead, so quite possible, but not in my time.

After I sold the CLS's, I had brief flings with the SL-3, Maggie 3.x, Quad 998?, and lots in between.  Retubing costs for amps, sourcing fancy types, and prior unsatisfactory results/cost has pretty much cut me off from tubed amps as a viable choice these days.  A preamp? - perhaps but I have a Pass L - which trounced my ARC SP-15; - I mean it was sad (do miss the polarity switch however) Headphone amp - perhaps, but I liked the Ragnarok more than the warmer albeit colored tube options at similar prices.  Coloration levels a magnitude better, and bass?  much better.  Oh yeah, a nice integrated amp too boot.

My favorite speaker of this century is the Verity Parsifal decidedly not a panel and driveable by tubes.  Still like the Pass X amps better than anything else on them, but, nothing really sounds bad on them - the spiritual grandchild of the ProAc EBS.