Racing sparks

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

Original poster: "Tom Luttrell" <tom-at-pwrcom-dot-com.au> 

I rebuilt my blower spark gap, 
http://www.webclot-dot-com//high_volt/images/toms_new_gap_2.JPG

This has allowed for a considerable improvement in airflow and streamer 
length. I'm now getting the occasional hit to the strike rail, something 
that did not ever happen with my previous gap.

This new gap just fires at a setting of 8mm with only the NST connected, as 
opposed to about 5 to 6mm for my previous gap. I put this down to the 
sharper rim of the pipefittings as opposed to the flat brass rod face of my 
first gap (http://www.webclot-dot-com//high_volt/images/toms_gap2.jpg).

Unfortunately it's too good. After about 5 to 10 seconds of operation I 
start to see racing sparks on the secondary.

My primary is an inverted cone (30°) and the coupling is probably a bit 
tight (JAVATC calculates it to be 0.17).

The way I see it I have the following options:

1) reduce input power via my new yet to arrive variac

2) reduce the spark gap (and hence firing voltage)

3) cut down the primary supports so it becomes a flat pancake coil

4) raise the secondary height.

Options 1 and 2 have the advantage of being easy but would negate the 
recent gain in streamer length.

Options 3 and 4 would require some major rework, including modifications to 
the mechanical method by which a 1/4 turn twist of the secondary locks it 
in place.

I'd be interested in reading any thoughts you may have on this matter.

Tom.