RE: Strange gap action

I didn't understand precisely where this 2.5" spark was.  It sounds like it
was arcing across the surface of your flattened PVC pipe?  If so, the
explanation is that surface arcing distance is much larger for the same
voltage as free-air arcing.  Surface arcing across PVC also tends to leave
permanent carbon tracks which promote further surface arcing.

The 0.5" gap may be somewhat on the large side and allowing your cap to ring
up to very high voltages.  On my single gap, set at 0.34", the breakdown
voltage was measured at 24KV.  Your tungsten electrodes may have sharper
edges which will tend to reduce their breakdown voltage, so it's hard to

I'm not sure the PFC cap you added in series to your tank cap is a good
idea.  I assume you meant that its value is 1 microFarad -at-18KV.  Since 1uF
is so much larger than your .02uF cap, the voltage division between the two
is going to put only 1/50th of the applied voltage across the 1uF cap, doing
very little to relieve the stress across your .02uF cap.  Further, PFC caps
tend to have very poor dielectric properties and will add considerable
series resistance to your tank circuit.

Regards, Gary Lau
Waltham, MA USA

		Original Poster: BunnyKiller <bigfoo39-at-idt-dot-net> 

		Afternoon all,

		    Just recently I have noticed my spark gap doing
something different that I
		have never encountered before. As the coil is running, the
spark gap fires
		between the electrodes as normal and then about every second
or two, it fires the complete length of the electrode assembly ( 2.5" ). Gap
type is a single set ( 2 electrodes tungsten 1/8" dia set approx.  .5"
apart, the tungsten is set into
		1/4-20 bolts (( used for adjusting gap width)) these
bolt/electrode assemblies
		are mounted in a 2" pvc pipe that has been heated and
"squished" to form an oval shape ). this is the reason for the 2.5 "
opening. Air is drawn over the gap
		assembly via a shop vac. Obviously the system is not
suffering from a lack of air
		flow  :) . btw  main system is  4 NST's -at- 15KV -at- .030 A
all parallel wired
		outputs (( 15KV -at- .120 A ))  primary is 3/8 Cu tubing -at- 15
degrees 13 turns .25
		bewteen turns. Secondary is 8"X30" (30" of windings)22awg on
		tubing. Caps are 1 homemade P.E. & Al plate for a measure of
.0224 mF (vertical form .060 " PE plates) run in series with a power
correction cap from the power company. ( it is rated at 18KV 1mF ) did this
to relieve voltage stresses on homemade cap. Toroid consists of 1-at- 4X10 and
on top of that one is a 6X16  ( both are aluminum flex duct)  and for
grounding  2 Cu clad rods 8' apart joined by flattened 3/8 soft Cu tubing.

		back to the problem ...  why do I get these long arcs ( from
furthest points
		inside of tube) when the actual electrode gap is only .5 "
and btw  these long arcs are above the gap set by at least .5" also.  ( very
loud sharp cracking noise  alot louder than the normal gap noise)

		Is it possibly a least resistant path due to slower airflow?
or is there some
		other mystical reason??

		hope i included enuf info

		Scot D