It's a process with numerous SS or Tube amps to choose. You have to audition the Krell and Parasound A21 hopefully with the Acoustats to determine what fits your listening experience.
If your buy new or used what is your budget?
If you want an SS amp that won't freak out when faced with electrostats, consider the one from Roger Sanders (formerly of Innersound) http://www.sanderssoundsystems.com/
If you prefer tubes as I do (for driving electrostats) I recommend one (or possibly two as monoblocks) McIntosh MC275's. The McIntosh Unity Coupled Circuit provides as much current per watt as just about any amplifier made, so it's well suited for driving electrostats.
Any amp stable at one. ohm. These are not easy to rive becauze they do present 1 ohm laods but employ fonick transforms thst friend's melted with an Aragon m0n0 block palladium 1Ks.
Instead try a favorite for low ohm loads the ICE powered H2O brand.
i wanna spend $2500 or below.
If you want to use SS; find an amp with MOSFET outputs. They will maintain stability at low impedance levels. One can practically arc weld with some MOSFET amps. I used modded Hafler DH-500s with Acoustat Model IIIs(in the early '80's) with great success(was a dealer, back then). I much prefer tubes, but synergism with electrostatics is harder to reach. Here's a suggestion: (http://www.avahifi.com/root/equipment/amplifier/fetvalve_amps.htm) You don't mention your pre, but tubes would be nice there, and would give you the ability to tweak the system's presentation to suit your tastes.
If you want a great stereo (actually 'dual mono') SS amp for around $2500+ look for a Mark Levinson 23.5 (not a 23, a 23.5!) 200W @ 8 ohms, and worked beautifully into 0.7 ohms! of my MartinLogan CLS's.
If on the other hand you want a great tube amp which puts out a very "current rich" 90W/ch you can't go wrong with a McIntosh MC275 Mk IV or Mk V; which are now selling used within your budget.
You don't mention your pre, but tubes would be nice there, and would give you the ability to tweak the system's presentation to suit your tastes.
I think this has become a popular misconception. If you want to roll tubes to tailor the sound of your system, you need a tube amplifier. In a preamp (with the exception of a PHONO preamp), the tubes aren't used for amplification, and therefore have little effect on sonics other than adding a certain amount of tube hiss to the signal (even in the more expensive units.)
Ns said, "I think this has become a popular misconception. If you want to roll tubes to tailor the sound of your system, you need a tube amplifier. In a preamp (with the exception of a PHONO preamp), the tubes aren't used for amplification, and therefore have little effect on sonics other than adding a certain amount of tube hiss to the signal (even in the more expensive units.)" In my experience, I've found tube rolling worked wonders in quite a few pre-amps over the years(especially my own ARCs), and particularly in units with tubed power supplies. Voltage gain is the purpose of most tubes in a pre-amp(just as in a phono stage), and they are in the signal path. Any tubes used in a pre-amp(or phono stage) need to be screened and certified very low-noise, regardless of the unit's cost.
look for a used symphonic line amp or amps--I have used 3 diff ones with my modded spectra 33 and they are a great synergistic match
Rodman, I don't know which ARC preamps you've owned, but the later ones with onboard phonostages (like the SP-14) use a single tube for gain in the phonostage only. The other tubes in a "tube" preamp provide source input buffering -- thus leveling the (input impedance) playing field for the various sources. This makes it easier for all the sources (including phono after being amplified in the phono section) to drive an amplifier.
Further, because tubes are high impedance devices, many "tube" preamps actually use solid state output stages because of their low (versus high for tubes) output impedance. Why? Because the lower a preamp's output impedance compared to an amplifier's input impedance (1 to 100 is considered excellent, 1 to 10 is absolute minimum) the more faithful the frequency response to the original source signal, and the farther the distance over which you can run interconnects (even single-ended interconnects) without signal loss or noise pickup.
So Rodman, if you've "found tube rolling worked wonders in quite a few pre-amps over the years" I'm not saying you're wrong, but I'd like to know two things:
1.) What do you mean by "wonders"? For instance, rolling an ultra quiet tube in place of a noisy tube is not a "wonder" it's just common sense. The sonics really won't change because a preamp if it's any good will remain neutral. The sound will come through against a blacker background if the tubes are quiet; for a REALLY quiet background, a quality SS preamp is just the ticket IMO.
2.) Where in the ARC preamp circuit is/are the tubes in question? If they are in the phonostage, they don't count for this discussion, because that exception has already been noted. If they (actually "it") is in the power supply, you have to be talking about an SP-8 (introduced in 1981) which did have ONE tube in an otherwise solid state electronically-regulated power supply. All other ARC preamps before and to the present, had/have ss power supplies.
Certainly in some of the 'all-tube' (except power supply) ARC preamps, there is ample opportunity to try different brands/types of tubes, but even ARC is always talking about better performance in terms of lower noise tubes, not in terms of better sonics (i.e. frequency distribution, detail etc.) Of course ARC has the (dubious) reputation for making the most SS-sounding tube equipment there is ;-)
By, "wonders" I meant what I said in my initial post. Obviously eliminating noise is not a, "wonder". Here are some others that have found what I have with regards to the benefits of tube rolling in pre-amps:(http://www.6moons.com/audioreviews/tuberolling/tuberolling.html) (http://www.audiocircle.com/index.php?topic=35170.0) Be certain to read the third page of the Six Moons article, where changing out rectifiers is discussed(though most of his rolling in in the gain stage). I've rolled tubes for customers and friends in pre-amps from ARC, Cary, Dynaco, Joule, etc. Whether an input buffer, gain stage, output buffer or rectifier; I've found all to affect the presentation of the unit, and provide a means to tailor the sound to the individual's taste. In my ARC SP-9's line stage gain block; The input signal was applied to the gate of an n-channel FET, the drain of which was connected in a cascade manner to the grid of half of the Siemens E188CC dual triode I was using(very much in the signal path). In the SP-11, each signal "stage" consisted of a FET and a Siemens in a cascode configuration. I liked the transparency the German tubes(Siemens/Teles) provided. My apologies to the OP for having taken so much of your thread to explain my experiences with tube rolling in pre-amps. Hopefully, some of this info will benefit you in your quest for a more musical system.
Rodman, I've no desire to split hairs with you because first, you obviously have walked the walk, and second, you're a tube guy, and that's all good in my book!
But I'd like to express my POV more succinctly while at the same time addressing the OP's rather colorful inquiry as to whether he's "bringin a knife to a gunfight"!
So let me put it this way:
One can enjoy far more sonic variety (assuming that's what one is after) rolling the gain stage tubes in a tube amplifier (regardless of whether the preamp is tube or ss) than one can ever have rolling the tubes in a tube preamp and using a ss amp. And I think it a common misconception when people assume the effect can be the same either way. Further, a (decent quality) tube amplifier is just as quiet as any ss amplifier; whereas I have never heard, in my own necessarily limited experience, a tube preamp that was as quiet as a decent ss preamp. And so, the bottom line for me personally (and in the words of the Divine Miss Midler) is "why botha?!" with tube preamps.
As for the part about "bringin a knife to a gunfight", well, yes, one better bring a gun (e.g. a Krell or similar beast) if using a ss amp to drive an electostat; because stats will always try and eat even modest output ss amps. While a knife, in the form of a modest output tube amp, will generally do just fine driving even a large(ish) stat panel; and the worst thing that will happen if a tube amp isn't quite up to the job (probably under 100W) is it'll clip softly -- but not go into oscillation and then cardiac arrest!
And finally, as everyone who knows me knows by now, I just happen to think tube amps sound best with stats ;-) And I now realize a lot of other people think so too!
I agree on all points. It seemed the OP was leaning more toward SS, and thus my first response(regarding MOSFETs, high output, no thermal runaway). Knife fight? Bring an M-16(why waltz when you can rock 'n roll)! The AVA amps I suggested would still give him the ability to tweak their presentation, via their driver tubes(and perfectly fit his price range). Personally, I left tube pres behind years ago, first for a Placette Passive, then my TacT RCS 2.2X(a radical departure from my minimum-signal-manipulation/eschew-anything-digital days). I plan to keep running my modded Cary SLM-100 monoblocks 'til the wheels fall off(ya gotta love those TungSol CTL roundplates and Sylvania 6SN7Ws). Plenty of power, bi-amping Maggies with a SS/transmission line bottom.
Another best-of-both-worlds hybrid amplifier, which gregadd is planning for his new MartinLogan CLX's, is the latest Moscode hybrid from George Kaye http://www.moscode.com/
And while I feel this is a great way to bring some tube signal preservation to voltage hungry speakers like Maggies, I'm still not sure I'd want a ss output device driving stats, despite the ability to tailor the sound with the driver tubes.
Simple: PS Audio HCA-2. On my 2+2's I've tried McIntosh, TNT-200, and Hafler 9500 but none came close to the new technology in the HCA-2. No noise, no hum, no heat, no strain. Stereophile "A rated" for a reason.