Tesla ? coil

From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Thursday, June 04, 1998 6:24 AM
To:  Tesla List
Subject:  Re: Tesla ? coil

Tesla List wrote:
> ----------
> From:  Terry Perdue [SMTP:terryp-at-halcyon-dot-com]
> Sent:  Wednesday, June 03, 1998 7:31 PM
> To:  Tesla List
> Subject:  Re: Tesla ? coil
> Raymond Koonce wrote:
> > Some time ago I visited the Science Place museum at Dallas Fair Park and
> > witnessed the "Electric Show".  There was a demonstration of a large VanDe
> > Graf generator (very impressive) and a coil quite unlike a conventional
> > Tesla coil.  It was a orizontally- mounted ~3 ft. diameter coil which
> > tapered to a ~4" disk from which the discharge (6-8 feet long) emanated.
> > The controller apparently had a rotary gap (completely enclosed).  The
> > only connection from the controller to the coil was by two thick cables.
> > Does anyone have an idea what type of coil this is?
> I've only been subscribed to this list a short time, but this is the first
> reference I've seen describing a tapered secondary. It reminded me of the TC
> I saw as a kid at Griffith Observatory, outside LA, I believe. I recall it
> as having a flat spiral primary of flat copper strap, and a tapered
> secondary with a round terminal with spikes on opposite sides. It discharged
> to the walls of the room, a few feet away. Does anyone know if there's an
> advantage to tapering the secondary this way?
> Terry
> terryp-at-halcyon-dot-com


Other than it's interesting appearance, there are really few advantages.
Some disadvantages include:

1. Lower Q and broader resonance band implies lower overall
primary:secondary transfer efficiency
2. The reduced coil radius of curvature at the top makes it more
difficult to prevent premature breakout from the top of the coil.
3. The tapered coil form tends to make windings want to slip a bit,
particularly on a plastic coil form

-- Bert --