ESL Amplifier

There were also two designs in Audio Amateur for tube based direct drive ESL amps.

I think the original post was about a solid state amp to drive ESLs... the problem with solid state parts is that they still do not do well with kV floating around...

I think the problems with the Acoustat amp revolved around heat and stability... both problems presumably could be overcome. I think it used "sweep tubes" in the output, but I haven't looked at it in some time...

Seems to me that you could make a decent ESL amp with some 4-65s or 4-125s or even 3-500s or 4-400s (larger than the aforementioned tubes) or similar transmitting tubes.

But it's probably easier and simpler to just do the xfmr step up routine in the end.

Beveridge made a direct drive amp as well... never saw one of them.


PS. a simple trick that has been published is to use the primary side of a tube amp (like a ST-70 or MkIII) with a light load on the secondary side (ie. 16-32 ohms) coupled from the primary with caps... gets you fairly large HV swing. Not as much as with a transformer in most cases, but surely enough to make 'em play.


2003-01-07 11:01 pm
Just my 2 cents, a direct drive esl amp would be pretty dangerous to have around. Thats a lot of voltage traveling through the speaker wires... if anyone who wasn't experienced were hooking them up there could be some serious risk.

I guess its not as much of an issue if you don't have kids or munching puppies or anything, but its much easier to isolate the high voltage with the use of a step-up transformer.