"The Mighty Corona Cone" (fwd)
---------- Forwarded message ----------
Date: Sat, 14 Feb 1998 11:57:28 -0500 (EST)
Subject: "The Mighty Corona Cone"
Chuck Curran wrote:
>Your secondary dimensions are close to my unit that is 15"
>dia. x 56". I use a 10 1/2" x 56" toroid whose centerline is
>12" above the top turn of the secondary. I have not seen
>any discharge in the top turns at all--so far!
>I would suggest that you may need to make a larger toroid,
>if your system has the power to handle something like
>40"-60" in diameter.
If I add a larger topload that will reduce the secondary resonant frequency
even lower, meaning I will need to add capacitance to keep the primary in
tune, which I believe will result in a serious mismatch to my half-a-15
>It would help to have more detail on your coil design--maybe
>I already missed that?
15 kV 30 ma neon xfmr with half of the secondary in use (ground to one end).
Capacitor : four old heat-sinked mica caps from 1920's Navy spark
transmitter in parallel - marked .004 each at 12.5 kV. Ought to end up with
.016 but I measure .02 uF cold, so I've been using .018 uF in my
Primary: 11 turns of 3/8" copper tubing, 26" inches in diameter, 1 turn per
inch, solenoidally-wound, ends up about 12" high.
Secondary: 5' long, 16" diameter cylindrical form made of narrow wooden
strips air spaced. 48" of #22 coated windings, space-wound for about 13
turns per inch. Secondary sits about 2/3 of the way into the primary.
>I ran through several checks on the
>resonance of your secondary bare and with toroid similar to
>yours. I would "estimate (guess)" that the toroid provides an
>additional 18 pf which would suggest that your secondaries
>resonant point of 134 Khz would drop to around 101 Khz--
>I'm curious why you indicated yours is 119 Khz with
toroid, pretty big difference.
A Tesla-coil design program I downloaded calculated the secondary at 148 kHz.
I measured the secondary's resonant freq as134 kHz bare and 119 kHz with
the top loading. But it is certainly possible that nearby metal objects
were loading the coil down. Since my garage is over-stuffed clearance is no
more than 4 feet between coil and other objects. I run it out in the
driveway, of course, but I was measuring with the nearby objects.
>Did you run the wire from your secondary all the way up and connect it to
the toroid?? Yes, I even confirmed it by ohming-out the connection between
top of the coil and the toroid (since I cannot see the wire when it ducks
behind the wooded form-end).
Thanks for going over this with me -- I'm eager to get more dramatic results
(you know, I've got the spark "fever"). I just borrowed a .05 uF at 15 kV
oil-filled cap from work which I could place in series with the .018 uF
parallel combination for a higher voltage capability with .013 uF value.
This would allow me to use the whole neon secondary at 15 kV. Hmmm... I'll
have to figure out how to handle the center-tap grounding versus grounding
the low end of the primary to get that circuit going...