Re: Spherical vs. toroidal top loads on tube coils

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 10/2/01 10:47:36 AM Eastern Daylight Time, 
tesla-at-pupman-dot-com writes:

> I'm pondering the construction of a tube coil using a pair of 833As, and a
>  roughly 4: diameter
>  x 24" long secondary.  I've noted that several current VTTC designs use a
>  small toroid on the secondary, just like a SGTC.

Dave,

The small toroid on a VTTC serves two purposes.  First it
acts as a corona ring to prevent the sparks from flaring off
the top turn of the secondary, and secondly it generally may
add 1" or so to the output spark length.   If the sparks go
over 29" or so, it is likely that sparks will flare off the top
turn of the secondary if a toroid or corona ring is not used.
The toroid does not have to be fancy.  I once used a cover
from a box of imported butter cookies, and that worked fine,
but didn't look very fancy.  A 7" diameter sphere would
probably work fine.  It will need a breakout point attached to
the top to permit spark breakout most likely.  I always use
a breakout point with VTTC's, otherwise, they give problems,
such as tube arc-over, and other voltage stresses, and they
may fail to breakout at all unless the coil is severely detuned.
Also, the sparks will probably be short without a breakout
point.  Solid state CW coils behave differently however.

John