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Re: 1500-3000 turn coils

Tesla list wrote:
> Original poster: "Metlicka Marc" <mystuffs-at-orwell-dot-net>
> antonio,
> i have often wondered if the shape of a inverse conical primary produces
> a somewhat inclined magnetic field? the reason i ask is that on my 10-1
> "candle stick" coil, an inverse cone produced a much better discharge
> then a flat spiral. i tried many diameters and tubing sizes for the flat
> spiral but the cone always did better. i thought that maybe this could
> be due to the field inclining into a point "so to speak" thus causing a
> stronger couple or density in the thin secondary windings? of coarse i
> could be wrong (it has been said that i think to much). if you could
> enlighten me it would be greatly appreciated.

An inverse conical primary produces a field that is somewhere between
the field produced by a flat spiral and a cylindric spiral. You can
say that the field is "inclinated" in the direction of the center of
the coil, and certainly the coupling with the secondary is higher 
than in a flat spiral with the same inner and outer diameters.
You can obtain the same results with coils of any shape, provided
that the coupling coefficient and the inductances are the same,
and the distances from coil to coil and from turn to turn are high
enough to prevent arcing. I believe that the original reason for
using a inverted conic coil was to keep the high-voltage end of the
coil far from the secondary and from the ground, in systems where
the inner side or the coil was grounded. Otherwise, I don't see any
special characteristic making it superior to a flat or cylindric
spiral. A cylindric spiral, that is rarely seen today, is not so
bad if made with enough radius to avoid arcing and excessive
coupling. It would minimize the length of wire required for a
given inductance, minimum radius, and turn to turn spacing.

Antonio Carlos M. de Queiroz