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HELP! Looking for 807 PP OTL circuit for electrostatics

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haiqu

haiqu

Member
Joined 2005
#1
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?
 
#2
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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  • Screenshot 2020-05-23 at 09.39.48.png
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#3
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
 
#6
haiqu said:
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?
Click to expand...

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
 
#7
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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#9
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.
 
#10
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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  • 807 OTL Electrostatic.JPG
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#12
haiqu said:
.... AUDIO June 1963....
Click to expand...


Thanks for this. Direct driving ESL's with tubes is so elegant. So Ive attached the two other pages of this article addressing the theory and build of the DD-amp in case anyone is inspired to have a go.
 

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