SMALL COIL

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

Finally have a TC project to report.  Built a small coil this weekend
with the following specs:

Secondary winding:	1.75" OD, 5.6" long
Wire size:				#36
Top load:				"Semi-toroid"*, about 3.5" OD and 1.5" thick
Approximate turns:	750
Resonant frequency:	Approximately 650 kHz
Primary:				3.5" OD x 1.4" long
Primary capacitor:	4 x 1900 uufd, ceramic filter caps in parallel
Primary transformer:	3 kV, 18 ma
Spark Gap:				Victoreen SGCA-2500D sealed voltage protector
Spark Frequency:		Not measured yet, probably several hundred/sec
Construction:			Rather crummy, I fear.  This is the "breadboard".

Results:

	2-1/2" plus streamers from #26 "breakout wire" taped to top terminal. 
Without said wire about 4" very hot streamers to a screwdriver in the
hand.  Get similar results with a 2" round brass doorknow for upper
terminal, but get a lot of discharge around the top of the winding. 
Almost no sound when there are no streamers.

	With the Victoreen gap replaced by a static gap set to "just fire" with
the capacitor disconnected get significantly greater streamers, but the
gap gets hot and stops quenching well so haven't made any measurements. 
Need to make a cylinder gap and give it a try.  Also have a problem with
occasional inter-turn arcs.  Don't think there are any crossovers in the
winding, but nor sure although I can't see any.  Winding this little
secondary by hand took over two hours.  #36 wire is strong enough to
handle, but small enough to cause problems when laying it on the form.

	All in all, a satisfying effort.  I'm sure others have gotten much
better performance from little coils, but this one pleases me.  One
thing I haven't done is to measure the primary current.  Although the
capacitor is well below resonance there must be a fair amount of input
power, as the Victoreen gap gets hot in a few seconds, the the spark in
the open gap is very, very bright.

Ed