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Re: Paul's design (no subject originally)
Post sent to wrong address? I got it from tesla-request-at-pupman-dot-com?
Anyhow...
> Could you folks review my proposed NST protection circuit schematic?
>
> 10 amp 0-140v variac
> 12KV, 60mA NST,
> Tank cap: .01uF Fair Radio cap
> Primary: 16 turns .25" Cu tubing
> Secondary: 6"x24" 22 awg
> Toroid: 6"x18" (approx) heating duct
Sounds good and solid. Additional NST and 0.01uF (or so) will increase
performance in the future, without significant need to modify any other
system components-- good flexible design Paul! If your primary is a flat
spiral, my design tool says it will tune with the tap between 12.5 to 13 of
the 16 turns. Good margin for corrections.
> Protection/Power circuit (the part i need help with)
>
> -20 amp EMI line filter before variac
> -safety gap after NST, middle grounded to RF ground
> -2 460pf 30kv doorknob bypass caps, one from each NST leg to RF ground
> -2 1800 ohm, 113w resistors, one on each leg after bypass caps and
> before sparkgap
All sounds fine to me. That filter will roll off above about 192kHz. This
is a hair above the resonant frequency of the primary tank, when tuned with
the proposed 0.01uF cap and 6x18 toroid. Personally, I would burn off a few
extra watts in the resistors to get the frequency down an octave below the
tank (4k per leg), but this extra few dB could be a moot issue and would
waste even more power when upgrading to more input power (double transformer
current = quadruple resistive losses).
> Does that sound okay? Will this setup be okay if I decide to add more
> NSTs for 90mA or 120mA? The bypass caps seem to be about what
> everyone else is using but I'm wondering if the resistor size/rating
> is correct. . .
The power rating is fine. With the 60mA tranny, they should be dissipating
only 10-15 watts max. 0.06^2 * 1800 = only 6.48 watts, but the
near-resonant 0.01uF cap could cause more than 60mA draw...
-Adam
adamsmith-at-mediaone-dot-net