Re: Pulsed Tube Coils

To: tesla-at-pupman-dot-com
Subject: Re: Pulsed Tube Coils
From: FutureT-at-aol-dot-com
Date: Sat, 4 Jan 1997 14:55:26 -0500
Subscriber: FutureT-at-aol-dot-com Sat Jan 4 21:50:03 1997
In a message dated 97-01-02 02:57:37 EST, you write:

<<       Hi John,
   
>snip
  >>  I was thinking of building a tube coil using a pair of
  >572-B's (basically heavy duty 811's) with a filtered DC
 > >plate supply of about 2500 volts,  the power supply would
  >have a output filter capacitance of about 15 UFD and the
  >>circuit would be the typical link coupled feedback setup.
  >>  But I was going to use a square or triangle wave signal
  >to drive a power mosfet (IRF-511) switch in the filament
  >center tap (cathode return) to gate the tubes conduction
  >> much the same as what a variable rate/dwell rotary gap
  >would do in a disruptive coil, or even use a audio 
  >source to modulate a fixed bias reference in the cathode
  >>return. Any thoughts on this approach?
   
  >>			Mark Graalman
   >>
 
 > Hi Mark,
 
 >Thanks for the suggestion,  I did some preliminary tests of your idea today
 at a low power, using a standard (12" spark) AC tube TC, and the results
were
 >excellent!   I used a horizontal output transistor because I didn't have a
 power mosfet.  I connected the collector to the tube filament, and the
 >emitter to ground (after of course opening the original filament-to-ground
 connection).  Then I connected my pulse generator across the transistor base
 >and ground.
 
 >I only turned up the main TC power part way because I was concerned about
the
 possibility of kickback destroying the transistor, the (TV-type) filament
 transformer, or the pulse generator.   But I did obtain a 5" spark, which
 >showed a nice staccato pulsing.   
  
 >In general, your technique may greatly simplify the pulse control circuitry
 >compared with what I've been using, and eliminate any potentially
undesirable
 >interactions with the grid-leak network.  It remains to be seen if a DC
 pulsed tube coil using this system will still require a tetrode and AC (or
 >other up-ramping voltage) on the screen grid for long spark production.   I
 definitely recommend pursuing this cathode-type control technique.  If you
 >try this technique Mark, I'd definitely be interested in your results.
 
>    John Freau
  
Mark,  All,      (update)

Today I did two experiments:  First I turned up the voltage all the way, and
got a nice 18" staccato spark most of the time, but since I was still using
the non-sync, pulsed AC system, sparks sometimes "broke into multiple spikes"
and lost spark length, due to incorrect pulse timing.   

 Next, I hooked up the DC power supply, and ran the system.  I only turned up
the power part way so far (I don't like seeing my components burn up!), but
the sparks seemed to be maybe a little better than using by grid controlled
DC staccato (neither case here using the "AC on the screen-grid" voltage
technique).  What I mean by "better" is the sparks seemed less "plasma-like".
 But it's hard to judge at low power.
But the spark was always shorter and broken up into multiple fingers, so I
suspect that the AC screen technique, (or something else that gives the same
result), will still be needed for long DC tube TC sparks, using this "lift
the cathode" control method.

John Freau