Out on a limb: 3/4" will only hold off 16 - 17kV anyway (or am I reading my
tables incorrectly?) So, is that not the appropriate gap setting already?
But, since this safety gap firing concerns you I will hazard a guess that: 1)
you have created a resonant condition in you RF filter which produces RF in
excess of the neon secondary voltage; or 2) your RF filter does not stop the RF
from the TC primary from getting back into the neon.
In my system I use a pair of (here's the plug, Robert!) Linsay Scientific
"Mega-Henry" RF chokes (which were developed for just this application) and a
safety gap AND NOTHING ELSE. These chokes work remarkable well - I can draw a
one inch gun-fire-loud arc off the TC primary end but only a regular 1/4 inch
neon-hiss off the other. My safety gap is set at 1/2 inch just in case (its
only an 11kV system) and seldom fires. In fact, since I reached optimum tune, I
don't think it has fired at all! So, my advice is (here's the rest of the
plug!): BUY THESE CHOKES!
Thinking I should be in Marketing,