Re: secondary coil form materials

[FutureT-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 7/9/00 10:46:22 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original poster: "John Morawa" <morawaj-at-interaccess-dot-com> 
>  Hello everyone,
>  
>  Can anyone recommend a material for secondaries coils?  Something that can
>  be found in a 4"-6" diameter.  Normally I use PVC but I understand that 
it's
>  RF qualities are not that great.  Of the two which would be better, acrylic
>  or polyethylene?  Or is there something that is similar in $ but better for
>  secondaries?  Also, for a coil of that diameter, what is the minimum wall
>  thickness to keep it rigid enough to wind.  Is 3/16" ok or is that too thin
>  or thick?
>  
>  Thanks for any comments,
>  John M.
>  

John,

Polyethylene is one of the best, acrylic is not as good, and pvc is
worse.  But the good thing is, it doesn't really matter.  You'll get 
the same sparks using polyethylene as with pvc.   I'm using a pvc
form now, and getting 42" sparks using a 12/30 NST.  However, it
is important to use a good dielectric for the tank capacitor.  In one
test, I replaced a polypropelene cap with a mylar (polyester) cap, and
had to use more than 15% more power to get the same spark length, 
and the sparks looked wimpier anyway.  Another important secret
for obtaining long sparks is to use more than the usual amount of
secondary turns (by using thinner wire).  This permits more primary
turns to be used, and reduces the gap losses.  I use 1300 to 1600
turns in my secondaries.  This technigue can add 10% or more to
the spark length.  Most TC books are riddled with errors and myths.
My coil can be seen at:

   http://hometown.aol-dot-com/futuret/page1.html

Cheers,
John Freau