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In Reply to: RE: By only ~4% (5V out of 120V)? posted by Sondek on March 25, 2016 at 07:35:05
Are these direct-drive OTL amplifiers? Oh, I guess you did mention they are from your Acoustats. Very cool. I use Beveridge 2SW speakers in one of my systems, also direct-driven. Although such amplifiers do put out high-ish voltage, sometimes the output voltage is much further increased after the secondaries, by use of voltage doublers, which is at the expense of current. But very very little current (at very very high voltage) is required to drive an ESL directly. Anyway, whatever one might have expected in terms of the effect of the AC voltage on vibration of the transformer, I don't doubt your direct experience. And those are probably unobtainium transformers, should one of them blow, so you are right to be conservative. I feel the same way about the power transformers in the Bev DD amplifiers.
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BTW, Beveridges also very cool. Working ones are scarce as hens teeth. I'd love to hear them. Too damned bad we live so far apart.
You are right. Direct drive OTL's. In reading Jim Strickland's notes on the copy of the schematic I have, the transformers output ~2,200 volts. He then employs voltage doubler to bring what the tubes see to ~5,000 volts.
So, 3200V across the stators. But they are not like conventional ESLs in that the diaphragm does not carry a charge; the diaphragm is low impedance (coated with aluminum)and driven, I think, along with the stators. Why this works, I have to sit down and re-think every time. However, because of the lack of high tension on the diaphragm, in fact the panels have lasted for 30 years, by and large. It's the amplifiers that cause problems. I am endlessly thankful for the help of "Steve O", an inmate on TubesDIY, who is also an EE and an owner of Bevs. Steve held my hand long distance as I solved a vexing problem with one of my amplifiers, which after all was done turned out to be a bad solder joint on one capacitor in the output circuit. After a while, I figured out it HAD to be something stupid like that, because I had been through and rebuilt the entire circuit, pretty much, and the amp was still oscillating.
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