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"The Mighty Corona Cone"
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From: Esondrmn-at-aol-dot-com [SMTP:Esondrmn-at-aol-dot-com]
Sent: Wednesday, February 11, 1998 5:43 PM
To: tesla-at-pupman-dot-com
Subject: Re: "The Mighty Corona Cone"
In a message dated 98-02-11 04:58:37 EST, you write:
<<
I added a 17" dia toroid made of 4" aluminum duct to the top of my 16" dia
48" long secondary, yet the top few turns are still streaming with corona.
In fact, the effect may be stronger with the toroid than without. It is a
solid, sharply-defined, glowing vertical cone streaming up and away from the
coil and topload.
Using my URM-25 signal generator with Hi-Z output and built-in VTVM indicator
(perfect for this job!) I measured the secondary's resonant freq as134 kHz
bare and 119 kHz with the top loading. My 11-turn primary is resonant at
about 116 kHz with my 0.018-0.020 uF tank cap, so it should be tuned OK. I
distrust the primary measurement to some degree, as I would expect the
resonance of the secondary to affect the primary .
Breakout was suppressed with the toroid in place until I used an inch of wire
to encourage the discharge out the side. The strikes and streamers from the
toroid were only slightly stronger than with just the top insulator bolt or a
vertical wire as top terminal.
As I increase the input voltage, the corona from the top few turns of the
secondary increase proportionally more than the streamer and strike length
from the top terminal. Before I redesign the exciter for increased output,
it looks like I need to supress this wasteful discharge from the top turns of
the coil.
Initially, I mounted the toroid directly on the top of the six inch ceramic
insulator. This placed the bottom of the toroid within a few inches of the
top of the coil. I raised it up at least 8 inches higher on a feed-thru
insulator stud - no difference, I was still running "The Mighty Corona Cone".
Short of submerging the entire coil in mineral oil, any suggestions?
Steve Johnston
>>
Steve,
Something is not right in a couple of areas here. First, I think the resonant
signal readings are suspicious. I have a 6" dia. secondary that is resonant
at 270 khz with no top load and at 132 khz with the large 5" x 40" toroid. If
I put your toroid (est 18 pf) on my coil it would still drop 100 khz down to
about 170 khz. Your coil is much larger than mine and adding the toroid would
not have as much affect as the self c of the coil is much larger - still I
would expect it to drop about 25 to 30 khz.
I don't understand how the bottom of the toroid can be within a few inches of
the top windings of the secondary when it is on a six inch ceramic insulator.
Still, I have mine mounted 10.25" above the top winding and have no problem
with corona. Is the coil extremely over coupled? Are you sure it is tuned
properly? I like to tune at about 1/2 power for the longest, hottest spark
(to a ground rod from a bump on the toroid) then move the tap out another
quarter turn for full power operation. What are you using for a power supply?
With a large toroid and a beefy power supply this coil should produce some
serious sparks. I would think 9 to 10 feet with a pole pig and rotary gap.
Ed Sonderman