tube amps and electrostatics

Sure(the 303 being the first)- But not until 11 years after Walker demonstrated his first truly full-range electrostatic speaker(in 1956). Around the same time that everyone else(McIntosh, ARC, et al) was bowing to SS and the output power demon.

I will let the more technologically astute (Atmasphere) explain the reasons why, but one of the most eye-opening and educational experiences for me happened about twenty years ago. I bought my first pair of Stax F-81 electrostatics (known to be a highly inefficient and brutal load) after hearing them sound glorious in a friend's system. My amp at the time was a NYAL Moscode 600 capable of 300w at 8ohms and 500w at 4 ohms; it is a hybrid design with ss output stage. I thought, surely the Moscode can drive the Stax with no problems. Wrong! The Moscode sounded thin, flat, and DEAD DEAD DEAD, with no dynamic verve. I tried various cables; no better. Then, for the hell of it, I tried a rusty old Dynaco ST70 (35w) that I had bought at a local TV repair shop for $50 and was my first pure tube amp. I figured, what the hell? Result: MUSIC!! The Stax's suddenly sounded the way I remembered them; sweet, refined, detailed, dimensional, and within an admittedly limited dynamic range, very ALIVE and dynamic. I drive my current Stax's with Manley tube mono's with great results.

Frogman hi, the Moscode 600 you mentioned not being able to drive the ESL's very well.
I believe that the Moscode 600 is a hybrid employing Mosfet output stage, even though it has a lot of watts!!, mosfets don't do current like a BJT (bipolar)output can
This is why it wouldn't drive the ESL's, as with ESL's the impedance curve can dive to below 1ohms at places and very capacitive as well, and for this a solid state amp should have a BJT (bipolar) output stage that is high current and be very stable into capacitive loads.

Cheers George

Bombaywalla, yes, Roger sets the impedance of his ESLs quite low, to make them more compatible with solid state.

...the Moscode 600 is a hybrid employing Mosfet output stage, even though it has a lot of watts!!, mosfets don't do current like a BJT (bipolar)output can
This is why it wouldn't drive the ESL's, as with ESL's the impedance curve can dive to below 1ohms at places and very capacitive as well, and for this a solid state amp should have a BJT (bipolar) output stage that is high current and be very stable into capacitive loads.

Georgelofi, I'm pretty sure that is not the right explanation. Keep in mind that a much smaller amp with tubes, the Dynaco ST-70, was able to play the Stax, with only 35 watts. Those older Moscodes had problems (IMO) unrelated to the fact that they used MOSFETs (IMO the topology itself was an issue).

We had customers play the Stax with our original MA-1s (which back in those days made about 100 watts) and they seemed to play well together. The old MA-1 was an OTL with no feedback and a fairly high output impedance, yet sounded find with the Stax. So 'current' is not the answer. Stable into capacitive loads- that makes more sense as that is something true of both the ST-70 and the MA-1.