Re: [TCML] Primary coils

[DC Cox <resonance@xxxxxxxxxxxx>]

Yes.  A flat Archemedian spiral helps keep the coupling to a proper low
value (0.12 to 0.14 range).  Inverted cone primary setups, in many cases
(but not all), produce overcoupling which is the main reason for racing
sparks.

If your sec coil is 4" dia or larger, then always use a flat spiral.  A 1 or
2" dia coil works good with an inverted cone spiral.

You calculate the surface area of the plates, then using the surface area of
just one plate, use the classic flat plate formula (in the archives) to
calculate the capacitance of your capacitor.
Sometimes, it's easier to just go to a local university and ask a friendly
researcher to measure it for you with a capacitance meter.  Many TV shops
also have them and could do the measurement for you.

I know the Leyden jar approach is classic, but MMC type caps are a much
better choice.  The terrible power factor of glass at RF frequencies sucks
away approx 30% of your input power and dissipates it as heat.  It can heat
the glass and cause it to crack.  The MMC type cap, pioneered by Terry
Fritz, is a RF snubber cap and is designed to handle higher frequencies.  It
uses a plastic dielectric with low dissipation rates.

Dr. Resonance







On Sat, Jul 11, 2009 at 2:00 PM, Joel Torgeson <joeltorgeson@xxxxxxxxx>wrote:

> Dear Coilers,
>
>     I'm sorry if this question has already been asked, but why is it that
> coilers use spiral primary coils? Other than arcing from the topload, is
> there a reason that the spiral configuration is better than just wrapping
> the primary wire around a larger base fit over the bottom of the secondary?
> I'm trying to build my first coil, and I'm not sure about how to make the
> primary. this isn't a necesarily large coil, so does the spiral add
> something that will help?Also, how do you find the capacitance of a
> leyden-type capacitor?
>
> Any help would be greatly appreciated.
>
>  Sincerely,
> Joel Torgeson
>
>
>
>
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