On Sat, 27 Nov 2004 13:52:07 +0000, Paul Burridge
wrote:

Hi gang,

Anyone know what differentiates a Tesla coil from any other old coil?
Is it simply that they all seem to be EHT types or is there some
particular quirk concerning the way they're wound? IOW, what sets 'em
apart?

thanks,

p.
Primary coil is a tank circuit (parallel LC usually) resonant with
the secondary coil. The secondary is usually placed inside the
primary coil.

While the primary is a parallel resonant circuit with a coil and
capacitor, the secondary is just a coil and series resonant, or a coil
with a large metallic body at the end to serve as a capacitor (spheres
and toroids are used to minimize corona loss)

A few turns of relatively large diameter wire or tubing in the primary
and a lot of turns in the secondary. 6:400 turns ratio is typical
enough for small systems, but that ratio isn't carved in stone.

The primary is wound as a helix or spiral, the secondary is wound on a
tube form, much longer than the diameter as a rule. Tuning the
primary to the secondary's resonant frequency is achieved via tapping
the primary coil with a movable tap.

Tesla or Oudin coils can easily produce hundreds of thousands of
volts. Lots of different forms and techniques are used to maximize
the output voltage - that's where it gets interesting.

The theory is simple - but building good coils takes experience.

They can be driven with high voltage transformers and spark gaps (the
most common technique) or vacuum tubes or solid state devices.

They are simple to build, good for high voltage experiments, producing
ozone, great visual effects, X rays, produce some RFI, etc..

There is a Tesla coil mailing list on the net that is very good. If
you want to build one (and I recommend it) they can be an invaluable
resource. http://www.pupman.com/ Lot of links to working tesla coils
and construction ideas.

Lindsay Publications www.lindsaybks.com is another source of books on
the topic (among others). Lindsay reprints books published at the
turn of the century (that would be the 1900's) on technology. It is
fascinating reading about tesla and induction coil construction - and
you can still build the stuff today with more modern materials. They
did have a paper catalog of their books in print - may still have it.

I built a few coils and a 1KW induction coil to drive them.