Mosca said:
BH,
Those look like... Futtermans! I almost bought a used pair, back in the '70s.
VTL175 monoblocks here, the ones with the 6 807s per side....
They
are OTL's...but they are a far cry from Futtermans. Futtermans had huge troubles with extreme oscillations which could be caused by overload, component failure or even layout problems. In many cases, they had a tendency to destroy themselves along with an honour guard of whatever equipment they were connected to at the time.
You were wise in passing on the Futtermans. There was a reason they were for sale used, I am sure.
Present day OTL's, whether Atma-Sphere...Joule-Electra..or any of a number of others currently available, are a compleatly different circuit.
These in particular are five 6SN7s as cascode drivers feeding fourteen 6AS7G power triodes. A nice additional safety feature is that each side of the 6AS7G dual-triode has a fuseable link which will fail before anything
could get out of hand. Not that this is at all likely, anyway. AsI said, it's a different topology which is a
lot more robust. I can (and do, to set bias and offset) compleatly disconnect the speaker load while the amps are on and warmed without so much as a complaint from them. They are pretty bullet-proof, actually.
beastie said:
From a fellow electrostat owner (Acoustat 3).
Greetings from a fellow member of the Flat-Panel See-thru Society! Those are SoundLab Milleniums in the pic.
.....BH