tube amps and electrostatics

Hi Atmasphere,
nice to have met you in person at RMAF2013. I always enjoyed listening to the Classic Audio Hartsfield & T1.4 & they were sounding very good with your amps.....

I believe that Roger Sanders has also done a great job with his s.s. amps - ESL Mk2 & Magtech - to drive electrostatic speakers. I listened to his speakers in the Sanders Sound Labs room & I really liked the sonics there as well. So, the s.s. world is not totally shut....
thanks.

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.

If you like tube amps and stats check out the virtual system of audiogon member Bruce_Weiland

http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1200440547

Really nice set-up he has there.

Play yes Atmasphere, but really you and I both know they were not able to give a flat 20hz to 20000hz into those hard loads.
They acted more like they had tone controls in them and made the FR look like a dogs hind leg.
I have a old friend that has two pairs of Stax F81's and not even his mighty Rogue Magnum 150 monoblocks drives them as well and with flat FR with a vice like grip as a good stable BJT amp can, like the big Krells and such.

Cheers George