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HELP! Looking for 807 PP OTL circuit for electrostatics
HELP! Looking for 807 PP OTL circuit for electrostatics
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Old 23rd May 2020, 02:15 AM   #1
haiqu is offline haiqu  Australia
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Default HELP! Looking for 807 PP OTL circuit for electrostatics

Recently I stumbled across a circuit for push-pull 807's that directly drove a pair of electrostatics. Unfortunately I omitted to bookmark or download the data and now I can't find it. I believe it was in a 1940s magazine but that's about all I can remember. I've checked the RTV&H index but it wasn't there.

Anyone?
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Old 23rd May 2020, 08:44 AM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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An amplifier employing 807s is nothing special, just a power amplifier with plenty of headroom is required for ES loudspeakers. The ESL has an audio matching transformer built in to isolate the input amplifier from the 6 or so kV static required to run the speakers.
See schematic attached.
The Williamson amplifier works really well with 807/6L6 as well as EL34/KT88 valves as the output stage.
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File Type: png Screenshot 2020-05-23 at 09.39.48.png (329.9 KB, 165 views)
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Old 23rd May 2020, 11:52 AM   #3
haiqu is offline haiqu  Australia
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Hi Jon,

The circuit I'm looking for drives the panels directly, no isolation transformers at all. I'm quite aware of how electrostatics work, having designed the electronics for a company in Melbourne which manufactured and serviced them. I'd like to use the 807 circuit simply because it would be an interesting exercise, not becaue I think it would be the optimum solution.

Cheers,

Rob
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Old 23rd May 2020, 12:13 PM   #4
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Sorry, I misunderstood you. It's a job to tell who knows and who doesn't.
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Old 23rd May 2020, 01:05 PM   #5
haiqu is offline haiqu  Australia
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Not a problem, you were just trying to help.
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Old 23rd May 2020, 01:47 PM   #6
316a is offline 316a  England
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Quote:
Originally Posted by haiqu View Post
Recently I stumbled across a circuit for push-pull 807's that directly drove a pair of electrostatics. Unfortunately I omitted to bookmark or download the data and now I can't find it. I believe it was in a 1940s magazine but that's about all I can remember. I've checked the RTV&H index but it wasn't there.

Anyone?
For the output stage , why not get a pair of 807/EL34 or similar power valves , strap as triodes and use an ultralinear output transformer ? Drive the UL taps and take the stator connections from the anode taps , make the bias supply negative . This works well in my limited experience with ESLs

316a
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Old 23rd May 2020, 04:37 PM   #7
RE 604 is offline RE 604  Germany
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Hello ,
I know only a circuit from the "Rennwald Hi Fi Stat" . It was from the sixties here in Germany . I cannot upload an attachment , I don´t know why , so send me a pm with your mail adress .
Kind regards , Alexander .
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Last edited by RE 604; 23rd May 2020 at 04:40 PM.
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Old 23rd May 2020, 08:57 PM   #8
RE 604 is offline RE 604  Germany
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Second try with another computer

Rennwald 01a.jpg
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Old 24th May 2020, 12:29 AM   #9
haiqu is offline haiqu  Australia
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RE 604: Thanks Alexander. Not the one I was looking for but still interesting. That gives me a place to start.

316a: I'm trying to avoid rare and expensive iron, which is why I'm looking for OTL.

BTW my original post is in error. Must have been a late 50's magazine article since electrostatics weren't invented until 1956.
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Old 24th May 2020, 04:03 AM   #10
haiqu is offline haiqu  Australia
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Stop looking, I found it filed under another category. The same magazine had two articles of interest to me. AUDIO June 1963.

Almost identical to the Rennwald circuit actually. In fact the article was written by Rolf Rennwald!
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File Type: jpg 807 OTL Electrostatic.JPG (92.9 KB, 104 views)
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Last edited by haiqu; 24th May 2020 at 04:15 AM. Reason: Add comment about article author.
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