tube amps and electrostatics

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)

Rodman99999,
this debate on MOSFET vs BJT has been duked out before many times & I do NOT want to get into it again. So, I'm writing this with a bit of trepidation -
both your references for MOSFETs seem to deal with MOSFETs used in a high frequency switching application (this is the key here - switching application) where MOSFETs are deemed better power devices than BJTs simply because MOSFETs are all-majority carrier devices (unlike BJTs which are bipolar carrier devices. hence the word "Bipolar" in BJT - both charges exist in this device - majority carriers in the emitter & collector & minority carriers in the base). Today's class-D amplifiers use power MOSFETs in their final output switching stage & for good reason as this stage operates at 10X the max audio frequency & we want to minimize the losses in this stage. For traditional class-A & class-AB power amplifiers, the output stage is NOT being used as a switching output stage; it's being used a continuously-variable analog output stage with high current capacity. I.E. the output stage is a gain stage & not a switching stage. There's a big difference here. You can definitely use power MOSFETs in the output analog stage as we see with Pass Labs, Threshold & many other brands. Not saying it cannot be done....

MOSFETs make better high frequency switches because at high frequencies we worry about the AC losses (CV^2f). These are the losses that are directly proportional to frequency & the parasitic capacitances of the device. Recovery time from off-to-on & on-to-off is also a big consideration in switching application & in MOSFETs this time is less than in BJTs as one does not have to wait for the majority & minority carriers to move from & get back to home base 'coz in MOSFETs there are no minority carriers!
MOSFETs are self-limiting current output-wise (higher temp means higher resistance, which means lower output current. BTW, if you did not realize this - this is negative feedback! But this negative feedback is localized to within the device) & all that is very well.
Output current-wise I also believe that BJTs do a better job - for the same amount of drain (MOSFET) or collector (BJT) current, the gain of the semiconductor device is higher in the BJT than in the MOSFET. Current in a BJT is linear relationship to circuit parameters like Vbe, circuit resitances, etc. In a MOSFET, the drain current has a square-law relationship to gate-source & threshold voltages.
At the very heart of it, the MOSFET is a voltage device (yes, it does convert input voltage to drain current, hence, the transconductance) but, naturally, it is a Field Effect device. And, intrinsically, the BJT is a current device. Yes, applying voltages to the terminals does create high electric fields but the applied voltages are meant to create electron flow (current) in a BJT & not setup a source-drain channel (like in a MOSFET).
MOSFETs have become very good power devices off-lately but I believe that BJts do a better job of high current delivery in analog circuits.

I am no fan of SS amps(except for driving woofers), but-
when someone makes blanket
statements, regarding MOS-FETs and ESLs; I have to take
exception.
Whatever their application; they still protect themselves
against thermal runaway, unlike BJTs, and can remain stable
in high-current situations. I
will side with those that have used them(past and present),
to great success,
in
their output circuits, ie: David Hafler's SS amps, Acoustat
TransNova TNT 200,
Van Alstine Synergy 450, Accuphase A-60, BAT VK-655SE,
Goldmund Mimesis8, Jeff Rowland M-9, to name a few(all Class
A or A/B). I've
not
heard any of those accused of being unstable, into any kind
of
real-world load. It's been my experience, as well as
others,
that MOS-FETs(in a correctly designed circuit) have no
problems driving ESLs. You mentioned PASS and I'll use the
following article, as my parting shot. Especially pay
attention to the portion entitled, 'Stretching Those
Muscles':
(http://dagogo.com/pass-labs-x350-5-amplifier-review)
Happy listening!

Rodman999999 You mis-read my statement on I vs R.
I said "that can almost double", the app word being "almost" you read what you wanted to see.
And here is the advertised specs of an Australian amp called and ME1500 and yes it can "almost" double all the way down to 1ohm 220-8 430-4 800-2 1500-1. And thats both channels driven at the same time!!

http://www.me-au.com/ME_1500_data_1.jpg

http://www.me-au.com/ME_1500_data_2.jpg

And even the smaller ME amps do the same amount of "almost" doubling. Show any Mosfet that can do these kind of figures, and like I said I'll show you a case for false advertising.

Cheers George