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Old 20th October 2004, 02:41 PM   #1
Volenti is offline Volenti  Australia
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Default Tube amps and electrostatic speakers

Since tubes typically run at a pretty high voltage, could they directly drive electrostatic spealers?

Would be nice to do away with the transformers in the signal path...
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Old 20th October 2004, 02:56 PM   #2
SY is offline SY  United States
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Yes, but not easily.

"Normal" tubes can be used for swings of a few hundred volts (good enough for e-stat headphones), but ESLs typically require a few thousand volts. So, you can use high voltage tubes and high-power high-voltage supplies. Dangerous stuff, expensive, difficult to stabilize, and very difficult to make reliable.
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Old 20th October 2004, 07:22 PM   #3
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As SY says the real high voltage stuff is VERY dangerous.... but the idea of using a smaller turns matching transformer from 400-500 V up to the ELSs is an idea of haven't seen much application of.

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Old 20th October 2004, 07:39 PM   #4
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even before "Speaker Builder" (1980?) was published there were several articles in Audio Amateur concerning ESL's and ESL amplifiers -- here's a good reason to go to the audioXpress website, order the CD-ROM and keep Ed Dell in business , issue 3/1977 (geez, my oldest son was born that year!) has a hybrid amplifier using a pair of 8068's as the finals. 600 Volts.

I would take issue with the author's use of a backwards filament transformer to derive the HV -- most transformers don't have the insulation to take the high voltage.
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Old 21st October 2004, 12:54 AM   #5
Paul W is offline Paul W  United States
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Seems like a zillion years ago, but I used TV horizontal output tubes (6DN5's, 35LR6's or one from that club) class A @ 3kv to directly modulate a DC arc (creating the worlds most impractical tweeter). Quite certain it would work for ESLs...it's been done several times.

Be EXCEPTIONALLY careful...a second chance with a high current high voltage supply is highly unlikely. "Normal" ESL power supplies, while dangerous, are fleas by comparison. Build a shorting interlock on the power supply, work with one hand in your pocket, life is more important, etc etc.
Paul
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Old 21st October 2004, 05:56 AM   #6
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On this site you can find more information about a project like this:

http://www.ultranalog.com/
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Old 25th October 2004, 07:41 PM   #7
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Acoustat has made the X, which is a 3 panel system with a direct drive OTL power amp.

The last stage is a SRPP made with 6HB5 (TV sweep tube) tubes.

This is worthwhile to copy, I've done it myself.

But let me warn you again: this is not a beginner project.
The amp and or powersupply can easily kill you !

Dick.
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Old 29th October 2004, 01:55 PM   #8
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Direct drive OTL amps for ESLs have been done many times.

You should be aware that the VOLTAGES ARE DEADLY.

(actually the B+ is high voltage high enough current...)

And that they generally require equalization for a flat response for a wide band ESL.


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Old 29th October 2004, 08:27 PM   #9
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I currently designing such kind of amplifier

Be aware, the only 4 diy otl amp I seen on the web use choke load.

A capacitive load+choke load= very bad ringing issue

the acoustat X use a SRPP topologie with minimal current trough (about 6mA, not enough!!!) Also, srpp are srpp and in preamp, this configuration don`t have the sonic qualitie that I like

The only way to bulid a good otl amp is to use a pure classA and resistor coupling or tube ccs.

That will require twice the voltage and the effiency will be VERY low but that seem to be the only way.

For example, my amp will deliver about 2100VP-P, will run at 2500V and will consume about 1400Watts at idle (like a house heating plate(1500watts))

Martin
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Old 30th October 2004, 02:41 PM   #10
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Quote:
Originally posted by etalon90
I currently designing such kind of amplifier

Be aware, the only 4 diy otl amp I seen on the web use choke load.

A capacitive load+choke load= very bad ringing issue

the acoustat X use a SRPP topologie with minimal current trough (about 6mA, not enough!!!) Also, srpp are srpp and in preamp, this configuration don`t have the sonic qualitie that I like

The only way to bulid a good otl amp is to use a pure classA and resistor coupling or tube ccs.

That will require twice the voltage and the effiency will be VERY low but that seem to be the only way.

For example, my amp will deliver about 2100VP-P, will run at 2500V and will consume about 1400Watts at idle (like a house heating plate(1500watts))

Martin

Martin, why do you think that 6ma is not enough??

Also what tubes are you intending to use for your project??

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