FW: Miniature coils contest?
Anyone built a small, <8" long secondary and < 0.5KW, coil
with high performance? By high performance I'm thinking
2x or more than the secondary length. Robert impressed me
with the following after my initial inquiry. For me it's a challenge
I can afford $$.
Did you hear about the coiler that stayed out to late. The first thing
his wife say as he walked through the door was, "Wire you insulate"
Sorry I think it's an old electrician joke.
From: Robert W. Stephens[SMTP:rwstephens-at-ptbo.igs-dot-net]
Sent: Wednesday, May 08, 1996 10:42 PM
Subject: Re: Miniature coils
>From: huffman <huffman-at-d0tokensun.fnal.gov>
>To: "'rwstephens-at-ptbo.igs-dot-net'" <rwstephens-at-ptbo.igs-dot-net>
>Cc: "'David Huffman'" <huffman-at-d0tokensun.fnal.gov>
>Subject: Miniature coils
>Date: Wed, 8 May 1996 11:51:04 -0500
>There doesn't seem to be much interrest in miniature coils in the
>I would like to summit my guess as to your small coils
>output. Would 8" streamers be close to what you got? This
>is truely a guess on my part. I was able to get 4" sparks from
>the "poor" system I threw together and it would seem that with
>a good capacitor and more sec. turns it would do much better,
>say by a factor of two.
>I hope to some day see a 'real' coil in operation in the flesh.
>One that exceeds its secondary length. I am an electrical eng.
>and this stuff still seems like science fiction.
Yup, not too much interest out there, but I thought there would be
more academic interest Guys!
Your posting got my own interest peaked so I threw together a
different little coil as follows. Secondary was #29 enamel copper on
the same size (1 & 7/8 inch OD black ABS) wound to a length of just
6.5 inches. Primary was 3 to 4 turns of #14 copper, solenoid with
diameter of 4.5 inches. Dual fixed gap spark gap with small blower.
Full 10KV -at-23 MA furnace transformer, two of my increasingly famous
Stephens Mega-Henry brand air core chokes, with safety gap across the
transformer, and a large aluminum topload made from two plastic
frizbees cupped together and covered with alluminum foil tape. For
caps I used two good transmitting micas, .0039 mfd-at- 20KV each yielding
0.0078 mfd. Operating frequency was about 850KHz. The streamers
walking around the topload were a full 10 inches long!, but you need a
darkened or totally dark room to best appreciate such a low power display.
Also the ozone and oxides of nitrogen from this little baby filled up
the lab with a very obnoxious and unbearable odor very quickly, an
effect which (luckily) I don't get with my large multi kilowatt coils interestingly
This was the best I could coax out of it with the furnace
transformer, perhaps with a 30 MA neon it would have hit my
guesstimated 14 inches posted earlier. Still, 10 inches represents
1.5 times the secondary length. Not bad.
The little guy I had mentioned before that was complicated by the
insertion loss of a coupling loop produced 6 inch streamers, and was
run from just 1/2 of the furnace transformer secondary.
Congratulations, your guesses where entirely within the infield of
I think there might be merit in establishing a contest, pick some similarly small
size as to length and diameter only, and also specify the transformer
which could be used (like a 15KV 30MA neon, or a 10KV 23MA furnace
transformer, operated at exact primary nameplate voltage rating) and let
participants do whatever they wish to do within only
those constraints to make the longest repeatable and therefore
verifiable streamer to a grounded target.
Since the very idea of a contest should be to inspire original thought
and creativity I think I would even open
up the field to allow derivatives of the two coil classical design or
even a typical 3 coil design now increasingly known as a magnifier.
However if multi coil designs are allowed, then the size restraint
becomes somewhat meaningless unless you were to, for example, specify
that the measured inductance of the final resonator must be equal to
or greater than the sum total of all preceeding inductances within
the rf circuit, but then there are clever ways of increasing system
charging voltage by resonating the RF suppression chokes with the
transformer secondary, so should these be included in the RF circuit?
Or should the ONLY criteria be the size of the transformer at rated
voltage and all other parameters be available to be freely
investigated? I think that might be the best.
What kind of prize could be awarded besides peer group status? Would
that be enough?
What do you think of this contest idea? Go ahead and post a copy of
this communication to the net if you wish Dave and we'll see what if
any interest there might be out there. Or maybe a contest of sorts
is already going on informally and the group doesn't have time or
finances for another one?
As always, Happy coiling!, rwstephens