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Re: Spark Gap Replacements


<< 
 >Subscriber: bert.hickman-at-aquila-dot-com Wed Jan  1 21:42:58 1997
>Date: Wed, 01 Jan 1997 10:06:26 -0800
> From: Bert Hickman <bert.hickman-at-aquila-dot-com>
 >To: tesla-at-pupman-dot-com
 >Subject: Re: Spark Gap Replacements
 
 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.
 > 
  >> 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? 
  
 >-- Bert,  Richard --
  >>
No surprises, but I really need to improve the system before real conclusions
can be drawn.   Richard Hull's hydrogen thyratron method may be  the "ticket"
to answering these quenching questions. 

 BTW, Bert, did you measure the quench-time of your system when it quenched
on the 1st notch?   More details such as  k value, frequency, and
 quench-time, would be appreciated.  I guess what I'm asking is the same
question you asked me, were there any surprises?   There seems to be a
question in my mind about what's really happening waveform-wise, during
pre-first notch times.  My quench time  was about 4 uS at k = .09, at 550
kHz, or somewhat longer than TC tutor advocates, yet I saw no "wave packets"
in the secondary RF.  This quench time gave me the longest sparks.  

Bert, did you try "degrading" your quench to the 3 rd notch (down from the
alternating 1 st or 2 nd), to gauge the effect on the spark length?

Happy coiling,

John  Freau