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re cap size
Stephen,
I would bet that your problems result from bad caps and bad gaps.
First, the caps. Plate glass turns out to be lossy. Also, the edges of
the foil have fairly high corona losses. Try running the thing in the
dark. You'll see the cap glowing purple. (I used to use glass and foil
too since I got it for free). Probably your best bet is to make the
Richard Hull style rolled caps. They are very successful and very
robust. You should be able to down load the instructions at the ftp site
ftp.funet.fi in /pub/sci/electrical/tesla. The commercial caps are
better I'm sure (still haven't verified that personally, but will
eventually (still making my rotary gap)), but the RHRC (Richard Hull
Rolled Cap) is fairly cost effective and you can probably have one sooner
than a commercial. Be sure to check the price total of all the materials
first though, because some people have found that a commercial cap isn't
much more expensive. That's probably due to their materials suppliers.
Next are the gaps. The best gap that I have used is an air blast gap.
However, I already had the compressor. You can get excellent results
from a very simple static gap.
Here's what I did: take a 1" rigid Cu tubing and cut it into 7 3"
lengths. Then take a piece of scrap wood that's about 6" wide and 8 to
10" long (2x6 works well). Make some little "fingers" that hold the
tubes down. They will stick in the tubes. These fingers need to be able
to move a little so that you can adjust your gaps. Next, set the spacing
to about 0.030" between each piece of pipe using a feeler gauge.
Finally, attach both your leads to the pipe using bulldog type clamps
(Kind of like an overgrown alligator clip) or something reasonable and
fire up the coil. Most people will say "what about air cooling?". My
answer is "I didn't have a muffin fan when I made the gap, and it works
for short runs anyway." When the gap gets hot, the coil basically stops
working and I need to wait a bit. C'est La Vie.
Chip