Re: sizes of the coil

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

In a message dated 7/28/00 3:48:18 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> are there standard sizes or dimentions to be used best for a TC.
>   
>  with this I mean like :
>   
>  space between primary windings

Jeroen,

THe difficulty of answering a question like this is that there are
various different basic approaches to building the TC.  For instance
if you use copper tubing for the primary, it will be spaced wider than
close wound PVC insulated #12 wire.  A person may decide to use
copper tubing not because it works better, but rather because it
looks nicer, or is easier to make a tap connection.  I found in my
work, that my coil when built with a close wound #12 wire primary
gave much better performance than built with copper tubing as a
primary, because I was able to use more turns, which raises the
tank surge impedance, which reduces gap losses.  I also had to
use more secondary turns of thinner wire to tune of course.

>  space between primary and secondary

For a smallish coil, this can be 1" to 1.5" or so.

>  ratio between primary and secondary

This will depend on the size of the capacitor, etc.  If you use a low bps,
which I've found gives the best "efficiency", then the ratio will be higher,
because you'll need a larger capacitor.

>  ratio of the secondary in with and length

This is not super critical, but the best "efficiency" will be obtained with a
rather small secondary which is somewhat tall, uses relatively thin
wire with high inductance.  The tradeoff is that a small secondary is
more likely to breakdown, or arc to the primary (from the toroid).

>  size of tank cap with secondary/primary size

This depends on the desired bps.  I found the best "efficiency" at low
bps, but folks may chose a higher bps for the sound effects, or because
they have a small capacitor, or want to vary the bps over a large
range etc.

>  turoid size to secondary size

Toroid size depends more on the bang size and input power than on
the secondary size.  A large bang size calls for a large toroid, but
the secondary could still be somewhat small, etc.  

In summary, there is no one best way to build the coil because the
best design will depend on the specific needs and application of the
TC.  For instance the builder may decide to use a toroid that is a
little smaller than optimal for longest sparks, because he wants to
get a lot of multiple streamers.

My coil which gives 42" sparks using a 12/30 NST can be seen at:

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

The design I use is basically the only way I was able to get 42" 
sparks from a 12/30 NST.  Using thicker secondary wire, a larger
secondary, a copper tubing primary, a smaller toroid, etc, will all
*reduce* the spark length somewhat.  (For best results, the 
secondary should be a little taller on that coil, 23" vs. 19".  I made
the secondary coil a little shorter to make the coil more compact
since it's a tabletop TC, but it hurts the performance some.)

Cheers,
John Freau