Re: anyone? shortform and inner primary?

I agree with all that has been said so far, re the problem of a short form
secondary lacking inductance, likewise the small physical size of the
primary with the same problem. I did experiment with the idea a few years
ago and had exactly the same difficulties. In fact I've just got out some of
the bits. A few years ago I came across a commercial boiler igniter that
used a small tesla coil. The primary circuit included an enclosed gap,
filled I believe with inert gas under pressure. The primary was wound on a
short piece of ferrite. Rather than the conventional single layer secondary,
the coil was wound in a series of sections, each with a good number of
layers, all connected in series, and separated by insulating discs . To
ensure HT isolation between the primary and secondary, the former was potted
in epoxy. As far as I can recall the resonant frequency was in the low
hundreds of kHz., The secondary length/diameter ratio was about 1.5:1.
Unfortunately I no longer have the bits, they got zapped! By the way the
current outpu was only a couple of mA or so.
----- Original Message -----
From: Tesla List <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, October 19, 1999 1:21 AM
Subject: Re: anyone? shortform and inner primary?

> Original Poster: Marco McClean <memo-at-mcn-dot-org>
> Tesla List wrote:
> > Original Poster: arrie <solva-at-xs4all.nl>
> >
> > Want to build my primary inside the secondary. Believe that with a tight
> > coupling much less input power is needed and a much higher q is
> > Tuning the primary will be more hassle but lifting will be easier on the
> > other hand.
> >
> > and: who has experience with very large diameter and short forms?
> > who?
>     Arwin, the inductance of a coil depends on diameter. Wide secondary
> would mean greater inductance, lower frequency of oscillation. And narrow
> primary coil would mean lessened inductance, higher frequency of
> oscillation. So to tune such a Tesla coil you'd have to tap the primary at
> much higher number of turns, resulting in less voltage gain per turn of
> secondary coil.
>     Then there's the internal arcing problem. And the waste of your
> painstaking work and half-a-mile of wire on a huge secondary coil-- unless
> the short form you're talking about is really short, in which case there's
> not much voltage gain going on.
>     These are some of the reasons nobody does this. Cool image, though-- a
> self-contained Tesla coil: just a squat black cylinder --like a lady's
> hatbox-- with a cord coming out the bottom.
>     Or a whoopee cushion!