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Re: Miniature Tesla Coil???

>Date: Sat, 02 Mar 1996 14:27:45 -0600
>To: tesla-at-grendel.objinc-dot-com
>From: paynet-at-interaccess-dot-com (Tedd Payne)
>Subject: Miniature Tesla Coil???
>
>I'm a high-voltage enthusiast and am slowly gathering info and parts to
>build my first Tesla coil, probably a "typical" coil of 2-foot or so output.
>
>This question, though, is a little different.  While I often hear of coilers
>wanting to build bigger and bigger units, I've never heard of anyone
>building a miniature TRUE Tesla coil (not just a little "flyback"-type
>circuit).  So here are my questions:
>
>1. has anyone done this, with the goal of making a very small coil with
>performance proportional to larger, high performance coils?  In other words,
>for example, maybe a 3-inch tall secondary with a 3-inch output discharge.
        My smallest coil is about 12 inches tall.  It produces about 2
inches of spark.  The problem with small coils is that as the secondary gets
smaller, the inductance goes down quickly, and high inductance is necessary
for good coil performance.  
        In addition, low inductance means higher operating frequency.  This
increases skin effect, thereby reducing the efficiency of the coil.  Also, a
high frequency coil tends to radiate more power as R.F. than a low frequency
coil.  Each of these reduces the performance capabilities of a small coil. 

>
>2. what would be appropriate specs for such a thing?
        Unknown, perhaps others will add insight here based on their own
experiences.
>
>3. what might be suitable sources of priamry high voltage (analogous to neon
>transformers in typical units)?
        I used a 6 kV 30 mA neon sign transformer for my little coil.  You
need enough voltage to operate a spark gap efficiently, unless you opt for a
tube or solid state coil.

>I think such a little coil would be very interesting to build, play with,
>and show off!
        My motivation for building one was so I could use it for
demonstrations and teaching purposes.  The one I built is still a little on
the large side for carrying around.  Perhaps an FET driven helical resonator
would be a better system for a mini coil.  Comments anyone?
Regards,
Mark S. Rzeszotarski, Ph.D.