Re: HV wiring

On 03/02/99 17:12:41 you wrote:
>Original Poster: Bob Misiura <misiura-at-nccoast-dot-net> 

>What may be an elegant solution is something I saw in a publication (but
>haven't tried).  Someone has built a top terminal using a plywood
>support to hold what looked like 1/2" copper tubing rolled into a
>generally spherical shape for the top terminal as well as the final
>turns of the coil.  The sphere over shadowed the top turns by about one
>diameter of the coil.  The tubing seemed to be spaced at roughly two
>diameters apart.


I place a rather small toroid about 2"-3" larger in diameter than the 
secondary coil form about 1"-2" above the last wire turn.  The big toroid 
is placed several inches above the small one.  Results are excellent ---
no upper coil or small toroid break out.  My favorite one is a 9" metal 
plate with a 3/4" metal pipe welded around the circumfrence.  I came out 
of an old x-ray machine where it was used for corona suppression.

The idea is shaping of the electrostatic field at the upper end of the coil.
To avoid a huge increase in terminal capacitance design and use as small 
of a toroid as it takes to do the job.  A little trial and error helps here.  
Annealed soft copper tubing filled with sand and gently bent around a
form is an easy way to go.  Or, of course, any small commercial plastic or 
styrafoam toroid covered with Al foil is a less permanent, but effective 

Richard Wall