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Old 9th May 2005, 04:19 PM   #21
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Yes, Iíve seen this suggested somewhere before, but Iím not aware of anyone building one (someone probably has though). I figure that if you had an amp with a 5K primary, thatís a step down to 8 ohms by the ratio of 25:1. Say you then wanted to step up for the ESL by a ratio of 1:75, as a reasonable example. What you really need then is a single transformer that has a 1:3 ratio, from plates to ESL stators. This will have high impedances on both ends, but Iíll bet a better transformer can be made at 1:3 than the two others combined.
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Old 9th May 2005, 08:08 PM   #22
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This (1:3 or similar xformer) could also be done using hv transistors or mosfets - might be better than what is usually done. May be we need to take page out of Susan's book Zero feedback Impedance thread and make our own.

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Old 9th May 2005, 11:06 PM   #23
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Ouch, why use MOSFETS when you can use still use tubes?

You don't need to switch to MOSFETs just because the voltage requirement dropped to within solid state range. Granted, it may work. In my experience (Zen et al), even these simple MOSFET amps suffer from rather high levels of phase intermodulation distortion (think FM) due to the highly non-linear internal FET capacitances which vary wildly with signal swings. That's why we love tubes! I'll bet that starts some responses, like poking a stick into a hornet's nest! Have at me...
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Old 9th May 2005, 11:38 PM   #24
hermanv is offline hermanv  United States
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Default High Voltage and watches

Yep, I did that; picked up a 1KW ham transmitter we had built 1,400 Volts on the plate cap if memory serves. Touched my metal watch to that cap while holding on nice and tight to the metal chassis .

Wow, best described as having your arm hit with a sledge hammer. Left some little black burn holes on my wrist. Did a good job of making sure I never did it again though.

There are some spectacular new transistors, IGBT, and MOS-FETs that reach 1200V and well past, not cheap of course and maybe too slow but a lot more drive current than those 833's and you probably only dissipate 500watts in the room instead of a KW .

Powerex is the first high volatge solid state co. that comes to mind, there are others.

Didn't the old Beveridge ESL have direct drive?
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Old 9th May 2005, 11:52 PM   #25
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When I said might be better ... I meant better than using bjt or mosfets into a standard xformer - I was NOT saying better than tubes. But it does not hurt to consider all the possibilities!

It seems that for most of us that direct drive electrostsats are dream and somewhat impractical, this leads to a transformer. Just because most amps out there are designed for 8 ohm loads the commercial electrostats are designed to interface with them (with a few exceptions - I once repaired a Accoustat, it used questionable (even for the time) op amps to drive tubes seemed a strange choice of circuitry). We DIY folks should consider what might work better, tubes to transformer to transformer to panels never made any sense at all, an extra lump of iron in there. And silicon (as opposed to silicon dioxide) to iron to panel we should consider what the optimum configuration looks like. Our amps can be special purpose and be all the better for it.

Well I've explained my thoughts a liitle better, but I expect pulling the stick out of the hornet's nest might not help to much!

Of course then there is problem of sourcing the iron - so now you might have to build the panels, wind the xformer, and build an unusual amp ... triple the fun!
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Old 10th May 2005, 12:15 AM   #26
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The 1:3 turns ratio (or so) transformer idea for tubes-to-ESLs really does make a lot of practical sense. I never claimed that a DD ESL amp was very practical; I did it to learn and just for the fun of making something like an ultimate statement. I would seriously like to work with a transformer winding expert, which I am not, to make a decent low-turns ratio HV design. It ought to be possible to achieve very high coupling, high primary inductance and low leakage inductance. In other words high bandwidth, although the capacitive nature of the load will be difficult. But in any case better than the two transformer case, I would think.
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Old 10th May 2005, 12:18 AM   #27
hermanv is offline hermanv  United States
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I didn't mean to make any value judgments, there is a good reason tube amps are still popular.

On the other hand it is perfectly possible to make first class amplifiers out of sand it just may be harder.

Either solution with a step up seems possible and makes more sense than first stepping down and then up again. i.e. If I wanted to built a transistor model I'd start with a couple of hundred volts instead of 50V for my main supply.

One big problem is that the panels have anything but flat reponse and the commercial speakers most likely were tuned with transformers in place.

Of course if it was all easy we wouldn't need the forums.
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Old 10th May 2005, 03:59 PM   #28
405man is offline 405man  Scotland
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One of the main advantages of tube amplification for direct drive of ESLs must be that the primary voltage swing on the output transformer is of a similar order of magnitude to that required to drive the ESL. Attached is the schematic of the Quad ESL63 from which it can be seen that the input is connected to 2 step up transformers with primaries in parallel and secondarys in series effectively providing twice the voltage swing. If each transformer was replaced by tube amplifier and the 2 amplifiers fed in antiphase then each amplifier would only have to swing by half of the required voltage which for conventional ESLs may only be in the order of 1.5-2 times the primary voltage and even for the ESL63s may still only be of the order of 3 times. This then has the advantage that each of the amplifiers only has to deliver half the total output power. The other advantage of tube drive with the ESL63s is that the protection circuit could be retained though you would need 2 of them. I hope that all makes sense


http://www.euronet.nl/users/temagm/a...esl63_sch2.jpg


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Old 10th May 2005, 05:19 PM   #29
hermanv is offline hermanv  United States
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Default ESL schematic

Typical British product, obscure and possibly clever all at once.

After a quick look I'm guessing the purpose of the 555 is to protect the power amp from ES panel arcing by momentarily placing a short accross the amplifiers outputs? I didn't see where the trigger for TR3 comes from.

I thought I'd read in an earlier post that the required swing was still beyond most typical tubes, something over a kilovolt? So a step up might still be required for any conventional power amp design. i.e you couldn't very well adapt an existing 6550 or KT88 design for this job.

My point being that once you take the step of getting a custom transformer designed and built, other design options become available.

Again I make no value judgements for or against tubes it's more to say that either tube or transistor design may well be equally difficult. The cliche, "no free lunch" seems to the point.

Really old TV sets (1950 to 60's) had very high voltage windings on their huge power transformers, we got that 1400V I mentioned from a vacuum tube voltage doubler so that transformer probably ran 800 VRMS unloaded. Wonder if any of those are still gathering dust in someones attic?
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Old 10th May 2005, 05:26 PM   #30
405man is offline 405man  Scotland
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The trigger for TR3 comes from a wire antenna close to the diaphragm and detects ionisation which occurs prior to arcing.

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