Toroid Speculations

>From kasper-at-kaiwan-dot-com Fri Dec  2 01:13 MST 1994

>It was Halloween.  I was getting ready to take my small Tesla Coil to a 
>friends to scare some kids [1] and I had just got a brand new torroid (20"). 
>I happily placed it on the top of the secondary, turned on the power, and...
>and...lots of noise, but no spark! At all!

>What happened?

	Assuming that the torid is metallic donaut thing, and large:

	Two things come to mind:
		The JOB of the toroid in conventional HV engineering is to
		provide a smooth, curved surface, with the highest voltage
		before breakdown possible.  It may have suceeded.  The
		volts are still there, they just don't jump clear, because of
		the toroid raigin the breakdown voltage.

	(This may be faq fodder:
		A point breaks down at the lowest voltage, an infinite flat
		surface at the highest, for a given "size" (diameter, roughly,
		a smooth sphere is usually highest, with toroid a good

		If teh coil was well and truly sharply tuned, chaning the
		top _will_ have detuned it.  detuned enough and the voltage
		will fall.

		Both of the above.

		Something else entirely....

>If I put the old top back (an upside down metal lamp cover), it works just fine
>(18" sparks).  When the new torroid is on, nothing at all, not even little
>sparks. (The noise was from the spark gap) 
	Clearly it was the toroid, then....

>This coil is powered by 15KV -at- .06A (neon sign trans). The secondary is 8"
>diameter, 3 feet tall, (500KC resonant freq). The primary is 5 turns 1/4"
>copper tubing around a 16" diam form. The primary cap is .007uf. 
	Sounds like a nice job...

>I know that this coil is not matched and has a low Q, but I still did not 
>understand the response from placing on the torroid.

>Does anyone have any ideas?
	using all safety precatioins, see what the spark at the top is NOW.
	The normal streamers are in part a function of the breakdown limits set
	by the shape of the upper electrode.  As Above, the toroid MAY be
	enough better at not breaking down that the voltage is not streamering
	(wotta word) off.

	If the voltage (spark length) IS lower,	I should juggle with the Tesla
	primary, as the easiest thing to change, to try to get it back in
	resonance.  If the toroid is bigger than the previous electrode, the
	secondary plus torid will be at a LOWER frequency, most likely.

Did i mention that i took my coil, which fits neatly under a table, which table
had a hole in the top, set the candy dish on top?  As each set of urchins walked
in, i hit the switch, I pulled small spark to me, as i grabbed the dish,
then a larger to the candy dish as i picked it up....