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Old 15th Nov 2017, 9:30 pm   #121
Ed_Dinning
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Hi Al, have a look at CVT's, capacitor voltage transformers
Used on power grids to read the line voltage at much lower cost than a wound one for 400Kv. Basically 2 HV caps and a transformer from the junction.
It works on AC and can be pretty accurate (used for bulk metering) if the frequency is stable.

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Old 15th Nov 2017, 9:43 pm   #122
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

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Originally Posted by astral highway View Post
How did you apply the varnish so absolutely immaculately without even the slightest run? I can do this on a flat surface but I would struggle with a tube...

Were you slowly turning the lathe at the time?
You got it! I applied a thin coat of varnish to stabilise the winding, then, after 24hours to let that dry, several thick coats, letting it dry for a day each time. After each coat I switched on the lathe, turning at about 15rpm for about 4 hours per coat to stop the varnish running. It worked much better than I hoped it would.
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Old 15th Nov 2017, 9:43 pm   #123
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

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Originally Posted by Ed_Dinning View Post
Hi Al, have a look at CVT's, capacitor voltage transformers
Hey Ed, will do, thank you. Are you thinking for me to apply this to measurements around my circuit? I'm building an EHT probe , but it's for RF signals, so it would still be useful for me to also be able to measure the pulsed DC in the power supply. Is that a suitable application for CVT's?
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Old 19th Nov 2017, 11:24 am   #124
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

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Originally Posted by mole42uk View Post
You got it! I applied a thin coat of varnish to stabilise the winding, then, after 24hours to let that dry, several thick coats, letting it dry for a day each time. After each coat I switched on the lathe, turning at about 15rpm for about 4 hours per coat to stop the varnish running...
Well, it is a I say, stunning work,Richard, with not a single flaw.
What’s your preferred varnish? Thanks again for your diligent and incredible work!
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Old 20th Nov 2017, 7:44 am   #125
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

I use whatever varnish i have lying around though the outside stuff seems to have a better finish.

Good to see your making progress Al.

Andy.
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Old 3rd Jan 2018, 2:50 pm   #126
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

After all that work, the bottom line is, how long a spark will it generate?
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Old 3rd Jan 2018, 9:07 pm   #127
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

View master, that’s the thing! We’ll never know. There is an approximate formula for valve Tesla coils, based on power in. According to that , we’d expect 70 cm plasma from the anti node, but the circuit was never realised with its new transformer. So it’s a moot point.

Somebody may care to take on the challenge: I will offer all the parts except the secondary coil for sale here before moving on to a EBay to recoup some of my spend.
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