Tesla List wrote:
> >From richard.quick-at-slug-dot-orgWed Jul 31 21:47:56 1996
> Date: Tue, 30 Jul 1996 23:49:00 GMT
> From: Richard Quick <richard.quick-at-slug-dot-org>
> To: tesla-at-poodle.pupman-dot-com
> Subject: help
> Quoting ZODAPOP-at-aol-dot-com:
> > HAS ANYONE TRIED TO BUILD THIS COIL?
> > I am having trouble with the IRF511 burning up.
> I have never built the driver for this project, but the
> resonating coil I have some experience with.
> > I have a 15000 volt neon-at-60ma. Can this coil be salvaged to go
> > with it? Or do i start over? I have the info from Walt Noon
> > (Tesla View)
> ... Big Snip, then quoting from the project notes:
> > The Tesla coil itself is constructed from a 3 foot piece of
> > 4" PVC pipe (if you go the hardware store & want to impress
> > them, tell them you need 3 feet of 4 inch Schedule 40).
> This resonator falls into the skinny "candlestick" type design
> that I really dislike. Coils work better when the physical length
> of the winding (not the wire length) are balanced against the
> coil form diameter. The ratio between the actual winding length
> and diameter is important. The ratio of the winding length to the
> winding diameter is known as the ASPECT RATIO (height : diameter)
> where the diameter always equals 1. Aspect ratios may be
> expressed by a single number such as "3.21". Please review the
> simple chart that I prepared (below) when selecting a coil form
> and the proper wire gauge: (All dimensions are in U.S.A.
> measurements, inches, feet, AWG, etc..)
> Coil Form Diameter Aspect Ratio Winding Length
> 3 inches 6:1 18 inches
> 4 inches 5:1 20 inches
> 5 inches 4.5:1 22.5 inches
> 6 inches 4:1 24 inches
> 7 inches 3.5:1 24.5 inches
> 8 inches 3:1 24 inches
> larger than 8 inches 3:1 multiply the coil diam. by 3
> This chart is a guide, not a definative last word. The data
> provided is the derived from actual resonator comparasions. You
> will find it hard to beat the actual "in use" performance of a
> coil based upon this simple chart. The coil outlined in the
> "recipe" we are quoting from has a calculated aspect ratio in
> excess of 8, closer to 9. This is off the chart. In this diameter
> coil (four inch) I have found that aspect ratios in excess of 7
> made miserable resonators.
> The other problem with this coil form is the excess plastic used
> in the construction. Schedule 40 PVC is very thick and heavy. Use
> thinner wall plastic tubing for the coil form. The thinner the
> wall, the lower the loss. This is even more important when
> winding resonators that are designed for excitation from lower
> powered CW or solid state driver systems.
> > Now drill a small hole each end of the PVC about 1/2 inch
> > from the top and bottom. Shove one end of the wire thru one
> > of the holes and leave about a foot of wire on the inside.
> > Take some tape and put it over the wire so you don't pull it
> > out like some dummy I know did (me). Now comes the winding...
> Don't ever make this mistake. I learned the hard way. Drilling
> holes and introducing wire inside of the coil form are lethal
> errors. While the coil may function fine with a CW or solid state
> driver system, when properly excited in a Tesla tank circuit the
> coil will fail internally. Now with this "candlestick" design
> advocated by the author you will never be able to properly couple
> the coil to a Tesla tank circuit (due to the high aspect ratio)
> IF you could if would short out through the inside of the tube.
> Having no experience with the solid state driver system I am not
> qualified to comment on any of the material past this point. I
> have no qualms about stating that secondary coil, built as
> described previously, would perform best if it was sawed in half,
> properly capped (no holes in the sidewall & no wire inside of the
> coil form).
> That is my two cents.
> Richard Quick
Everyone, re-read this post! It's worth more than two cents! In blown
time and effort, alone, it is worth many, many dollars. Not to mention
the valuable materials lost. This mimes our own experiences here in
Richmond. The table of aspect ratios is a real valuable asset to young
or beginning coilers for a good performing secondary right out of the
chute! Another good "Quickian" post.
R Hull, TCBOR