Re: Spark Gap Replacements

To: tesla-at-pupman-dot-com
Subject: Re: Spark Gap Replacements
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
Date: Wed, 01 Jan 1997 10:06:26 -0800
Subscriber: bert.hickman-at-aquila-dot-com Wed Jan 1 21:42:58 1997
Tesla List wrote:
> 
> Subscriber: FutureT-at-aol-dot-com Tue Dec 31 22:56:47 1996
> Date: Tue, 31 Dec 1996 16:02:10 -0500
> From: FutureT-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Spark Gap Replacements
> 
> Bert,  All,
> 
> Bert, you also mentioned (in your TCBA article) your interest in using solid
> state switches to replace a spark gap at low voltages.  Lou Balint and I,
> (working independently), have done some very preliminary work in this area.
>  We both used horizontal output transistors to replace a spark gap in the
> tank circuit of a TC.  This was not a typical solid-state TC, --- there was
> no oscillator circuit operating at the resonant frequency.  The design was
> exactly like a typical spark-gap TC, except that the spark gap was replaced
> by a transistor.  The capacitor was charged by the power supply, then the
> transistor was turned on using a pulse generator, transistor "on" time could
> be kept on for various time periods to simulate a quench time.  When the
> transistor was turned on, the tank resonated until the energy was depleted
> (damped waves).  I was unable to obtain any spark output from the secondary
> coil, although I was able to draw off a 1/2" spark using a screwdriver.
>  Power input was low, and DC power supply voltage was about 150 volts.  Best
> spark occured when "quench" occured at the first RF notch.  A small neon bulb
> placed at the top of the secondary coil lighted most brightly when "quenched"
> at the the first RF notch.  Resonant frequency = 500 kHz, Pulse rep. rate =
> 200 to 1000 PPS.
> 
> Lou Balint of PA, found the same results as I did, however he was able to
> obtain a 1/16" spark from the top of the secondary (spark emitted without
> being "drawn off" ).
> Unfortunately, at this slightly higher power level, the transistors ( 2)
> burned out in a couple of seconds.
> 
> In our work, we did not use back to back reversed transistors, I used one
> transistor, Lou used two in parallel.
> 
> The purpose of this work was to explore the benefits of fast "quenching", and
> avoid the difficulties of 1st notch quenching in actual spark-gap TCs.
> 
> Happy New year, and Happy Quenching!!!
> 
> John Freau

John and all,

Thanks for the update! This is an area I'd like to further explore when
time permits, though probably with power MOSFETS or IGBT's instead of
straight bipolars, for the same reason - investigating quenching. In
your work, did you see any surprises, or did experiment seem to match
theory? 

BTW, the "article" in the TCBA was actually a copy of my original letter
to Harry requesting membership back in May. At that time, Harry asked if
he could publish it, I agreed, and was pleasantly surprised to see it in
the latest issue!

Safe coilin' and happy New Year to you, John!

-- Bert --