Re: Location of Primary relative to Secondary???

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Justin Hays by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pyrotrons2000-at-yahoo-dot-com>

Hi Dan,

> Where should the secondary coil reside relative to the flat plane
> of the pancake primary coil?  Should it be level with the base of 
> the secondary coil or is this something that has to be adjusted 
> during operation.

Most people like to have their primary coils aligned on the same
plane as the bottom secondary coil turn. With tiny coils and monster
coils, this will always give OK results.

Other ways of doing it include raising or lowering the secondary
relative to the primary to adjust coupling. I've found that flat
pancake coils actually undercouple somewhat --- this is cured by
either raising the primary or lowering the secondary depending on
your construction techniques.

With SSTC's such as yours, lots of coupling is necessary for good
results as it is continuous wave. But with spark gap coils, you'll
soon find that that degree of coupling is destructive to the
secondary coil, and that the system will be very inefficient. You
want a very loosely coupled tesla transformer with spark-gap types.

Flat Pancake: Reliable "always works good" results, but may not be
enough coupling for optimum performance. Coupling can usually be
adjusted easily by raising or lowering the secondary in relation to
the primary.

Inverse Cone: Gives more coupling than a flat primary, but may be too
much if overdone. TCBOFW's (of Fort Worth, TX) Warthog coil has a 19"
secondary and a very large 30 degree inclined primary. The arcs are
extremely hot and white. I favor this type of primary...the more
power you can cram in the secondary the better. I think about 20 to
30 degrees would be optimum, but it depends on your setup.

Helix: Great for SSTC's, horrible for spark gap types...period!

Spacing between the primary and secondary: Doesn't really matter. For
coils under 1kVA, 3/4" is good. For coils between that and 5kVA, I
use an inch to 1.5 inches. For our 12" coil running 15-20kVA, we used
about 1.5". Of course if you're running high primary voltages (28.8kV
or higher), you'll need more spacing to prevent flashovers.

So that's primaries in a nutshell!

Take care,

Justin Hays
KC5PNP
Email: justin-at-hvguy-dot-com
Website: www.hvguy-dot-com