>  I just ripped out the power supply from a microwave oven that
>  was rated for 700W and operates at about 15-20kv.

>  Has anybody had problems with this? because I was thinking 
>  that the spark gap arc could draw too much current from the
>  transformer an it would over heat too rapidly.

A good reference book to read on current limiting is:

Henry L. Transtrom, orginally published: 1913, second edition
1921, Joseph G. Branch Publishing, Chicago; Reprinted 1990,
paperback - 247pp, ISBN 1-55918-054-4. Available from: Lindsay
Publications, Inc., P.O. Box 12, Bradley, IL. 60915,  Voice -
815-935-5353 ; Fax - 815-935-5477... 
Lindsay order number # 20544, $ 11.95. Lindsay also offers a good
selection of Tesla literature, classic electronics publications,
reprints, and T-Coil Design software.

Anyway the transformers that are covered in the book are
constructed identical to a microwave oven transformer, if wound
for a slightly higher output voltage. Several adjustable
inductive current limiters are pictured (with construction
details) for use with these transformers as Tesla power supplies.
One current limiter is made from a stripped down spare xfmr core.

I like the use of some resistance in series with inductive
current limiting to "smooth" out the inductive delay. 

... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12