Re: A 1/4 wave Tesla coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <paul-at-abelian.demon.co.uk>

Skip Greiner <sgreiner-at-wwnet-dot-com>:

> I thought that some of you might be interested in a
> true 1/4 wave coil.

Er, is there another sort of less-than-true quarter-wave?

> Wire length: 880'. This corresponds to about 280khz

Irrelevant.

> Free air resonance: 400khz
> Ctop: toroid 8" x 25" dryer duct with aluminum foil coating
> Ctop capacitance: ~22pf
> Secondary resonance with Ctop: ~280khz

> The output sparks are very thick and fat but only reach 60"(+).

Yes, your toroid is far too big. Why so big?  Perhaps you are
following an old myth and trying to pull the resonant frequency
down to that of the wire's straight-line resonance?

The original un-coiled resonant frequency of the wire is irrelevant.
Don't try to match this by piling on unnecessary topload. Instead, use
just enough topload to delay the onset of breakout. Reduce your
coupling before you try this to prevent damage to the coil. My guess
is you could gain up to another 25% spark length, with resonance
around 340 kHz, if you relieve the coil of its excessive Ctop burden.

See comments on the wire length myth in 
http://www.abelian.demon.co.uk/tssp/misc.html

A greater-than-optimum sized toroid is a recipe for hot, short, fat
arcs. Just what you want if you're powering an ion engine, but
probably not what the average coiler is aiming for.

BTW, Skip, your secondary is quite an interesting construction. I'll
bet it has a rather high Q factor and would make a fine CW coil.

Regards,
--
Paul Nicholson,
Manchester, UK.
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