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Re: Top Terminal Experiments
From: ghunter-at-mail.enterprise-dot-net[SMTP:ghunter-at-mail.enterprise-dot-net]
Sent: Monday, November 24, 1997 4:33 PM
To: Tesla List
Subject: Top Terminal Experiments
I've been experimenting with different sizes & shapes of top
terminal on my 4.5" x 23" coil. The setup is a "bargain basement"
classic. Power supply is a 15kv-at-30ma neon. Primary is ten
turns of stranded #8 copper wire wound on a plastic cake keeper lid.
Secondary is 460 turns of stranded #22 hookup wire wound on sch
40 pvc. Cap is four wine bottles (yeah, I'm that bottle cap guy) in
parallel for .0056uf. I'm using two spark gaps made from spherical
brass drawer knobs. Protection is chokes, power resistors, and
safety gaps. Local juice is 50Hz. While some more vocal
subscribers might disdain my "hillbilly" approach to coiling, I had
to stay within my means, so compromises were neccessary.
The first terminal was a 9" x 2.5" toroid. The foundation was 2.5
inch round flexible foam (this is sold in variety stores as a
floating pool toy) bent into a donut and covered with aluminum tape.
I put in a center disk covered with foil. I rubbed it down to a
fairly smooth finish. I mounted it several inches above the top of
the secondary on an upturned plastic tumbler. On first firing the
coil produced much corona but only about 6" sparks. I also
had a bad case of top turn corona. After seeking advice from this
list, I lowered the toroid so that its bottom lip barely overlapped
the top secondary turn. This eliminated the corona leakage, but
increased spark length no more than an inch.
Following more advice from the list, I made a bigger (13" x 2.5")
toroid from the same material. This one turned out even smoother &
nicer looking than the first. I had to increase primary inductance
to get sparks, so the bigger top hat obviously lowered the secondary
frequency. I only observed a marginal increase in spark length,
mostly 6" with an occasional 8" streamer. On both toroids, sparks
originated mostly from the outer rim of the donut and moved outward
and slightly upward.
The latest terminal is a 7" plastic toy ball covered with foil.
Smoothness is not as good as on the toroids. Tuning for this
terminal is the same as for the big toroid. The first thing I
noticed was that breakout streamers were both longer and thicker,
with many forked sparks exceeding 12". Spark direction is mostly
random, but the biggest sparks tend to break out near the very top
of the ball and move upward at a steep angle. Top turn corona is not
a problem, despite the lack of shielding. The ball is just sitting
on top of the pipe. The ball has a couple of "hot spots" which
produce many long sparks. I plan to cover these with teflon tape to
see if I can coax even longer sparks from the sphere. I can't
believe the dramatic improvement in performance from such a minor
change in setup.
I've also been "mapping" the RF field around my coil with a
florescent tube. I've noticed a very marked change in the shape of
the RF field just from changing from a toroid to a sphere top
terminal. More on this later. Thanks for all the help.
Greg