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Tesla ? coil - Griffith Observatory
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From: D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent: Saturday, June 06, 1998 1:31 PM
To: Tesla List
Subject: Re: Tesla ? coil - Griffith Observatory
to: Terry
The advantage to slowly tapering the coil is to slowly reduce the
turn-to-turn capacitance as you go up the coil. This diminishes the
problem of corona from the top turns of the coil where in a solenoidal
inductor the last turn abruptly reduces the capacitance to 1/2 its normal
value and corona streams off the top turn breaking down the insulation and
eventually the coilform. The complete evolution of this process was
discovered by Tesla and goes like this: solenoid --- triangle -- flat
spiral (shrunken form of triangle). Many flyback type high voltage
transformers also wind the outer few layers with reduced turns or spacewind
the outer turns to reduce the capacitance slowly to prevent these problems.
I had once seen a photograph of the Griffith coil in its dual triangle
configuration operating in a horizontal mode but can not remember where I
saw it. There is a group locally that does occasional work on the coil and
might have more information. I think Bill Wysock might know who does it or
perhaps he is a member of that group.
DR.RESONANCE-at-next-wave-dot-net
> From: Dan Murphy [SMTP:danmurphy-at-1stnetusa-dot-com]
> Sent: Friday, June 05, 1998 6:48 PM
> To: Tesla List
> Subject: Re: Tesla ? coil - Griffith Observatory
>
> Good memory, Terry -
> Having visited the Tesla Coil at Griffith Park recently, I can
> attest to the accuracy of your description. Gene Waldo and I went there
for
> the specific purpose of viewing the coil, and watching it demoed. It does
> indeed have a round discharge terminal at the top of its tapered
secondary,
> with 2 spikes on its circumference, right and left sides, to focus the
> output. There are grounded plates mounted in the walls on either side, 4
or
> 5 feet from the terminus, to which the sparks fly unerringly. It uses a
> rotary gap, I believe, but the only parts of the apparatus that can be
seen
> are the primary, secondary and terminus. Attempts to gain access to the
> inner sanctum for a look at the power supply, etc, were unsuccesful. The
> tour guide gives a canned speech about Tesla and the principles of the
coil,
> but it seemed like something he memorized, and he didn't really know all
> that much about coils and their underlying principles. Still, it's a fun
> show, lighting up neon and flourescent tubes with no wires, and
> demonstrations of the skin effect. Still, nothing like KVA Effects and
Brent
> Turner, the Million Volt Man. Now, THERE'S a Tesla demonstration!
> As for the original Griffith Park coil, we were told it came from a
> carnival, and that it was 60 or 70 years old. Nothing was mentioned about
it
> being half of an original dual secondary set-up. No one could shed any
light
> on the efficacy of the tapered secondary, other than it might lessen the
> chance for arc-over discharge, as it isn't equipped with a strike rail.
> Might have some effect on coupling, also. We decided it wouldn't be worth
> the effort to build a tapered coil form for winding such a beast... But
who
> knows, maybe it is!
>
> >----------
> >From: Bill Noble [SMTP:william_b_noble-at-email.msn-dot-com]
> >Sent: Thursday, June 04, 1998 11:45 PM
> >To: Tesla List
> >Subject: Re: Tesla ? coil - Griffith Observatory
> >
> >the coil at the Griffith Observatory (in griffith park, in the Hollywood
> >hills) is half of an older coil - it is run daily for visitors. There
is a
> >data sheet available on the coil - perhaps the observatory has a web
site??
> >I haven't checked for that. The original coil had two tapered
secondaries
> >and the primary in the middle, if I remember the brochure correctly.
> >And,yes, the coil is still there.
> >-----Original Message-----
> >>
> >>I've only been subscribed to this list a short time, but this is the
first
> >>reference I've seen describing a tapered secondary. It reminded me of
the
> >TC
> >>I saw as a kid at Griffith Observatory, outside LA, I believe. I recall
it
> >>as having a flat spiral primary of flat copper strap, and a tapered
> >>secondary with a round terminal with spikes on opposite sides. It
> >discharged
> >>to the walls of the room, a few feet away. Does anyone know if there's
an
> >>advantage to tapering the secondary this way?
> >>
> >>Terry
> >>terryp-at-halcyon-dot-com
>