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Re: Pulsed tube TC work


From: 	randy-at-gte-dot-net[SMTP:randy-at-gte-dot-net]
Sent: 	Sunday, November 09, 1997 1:19 PM
To: 	Tesla List
Subject: 	Re: Pulsed tube TC work

Tesla List wrote:
> 
> From:   FutureT-at-aol-dot-com[SMTP:FutureT-at-aol-dot-com]
> Sent:   Saturday, November 08, 1997 5:09 AM
> To:     tesla-at-pupman-dot-com
> Subject:        Pulsed tube TC work
> 
> All,
> 
> I did another test of a tube pulsing technique suggested by Mark
> Graalman some time ago.
> 
> Previously, I used a negative 500 volt
> pulse to the tube grid to keep the TC *off* for a few ac half cycles
> between TC *on* times.  Mark suggested using a solid state
> device to *lift* the cathode from ground to create the *off* times.
> Previously, I tested this idea, but used a pulse generator to
> control the tube coil.  Using the pulse generator, the on/off times
> were not synchronized with the incoming ac, which can cause a
> lot of distructive kickback to occur, and required extra choking
> and bypassing in the supply circuit.
> 
> In this new test, I used a timer circuit to turn the TC off for a
> adjustable number of half cycles, and then allowed the TC to run
> for one half cycle, and the process repeats constantly.  The
> result is a steady pulsing of the spark, and the rate of pulsing
> can be adjusted from 30 pulses per second to as few as 2 pulses
> per second.  The appearance of the spark is the same as in my
> original grid controlled method, only the method of controlling
> the spark hold-off is different.  This cathode lifting method is
> simpler than the grid method because a negative 500 volt DC
> supply is not needed.
> 
> The cathode is lifted by installing an ordinary transistor between
> the cathode and ground, with emitter to ground, and collector
> connected to the cathode.  The timer circuit controls the
> transistor base.  Transistor switching occurs only during TC
> *off* times.  The transistor used is a TX-183S, but any suitably
> rated transistor would work.
> 
> As the pulsing rate is slowed down, the number of spark
> streamers decreases until there is only one 17" long straight
> swordlike spark which pulses rapidly with a rat-tat-tat, or
> *staccato* type sound.  As the pulse rate is varied, the sound
> and spark appearance changes in an interesting way.  The
> coil oscillator uses a 4-400A transmitting tube.  This TC is an
> ordinary tube TC with the control circuit added.  The transistor
> does not act as a spark gap replacement.
> 
> Besides the advantages mentioned above, the pulsed method
> allows for a less robust tube to be used, since cooling occurs
> between pulses, also the average input power is much lower
> since the TC is off most of the time.
> 
> In another previous test, I ran the TC on every positive ac half
> cycle, but allowed it to run for only part on each half cycle and
> varied the spark duration between 1/10th and 1/3rd of an ac half
> cycle, but this caused three disadvantages:
> 
>    1.   sparks decreased in length
>    2.   sparks lost brightness
>    3.   power input decreased only slightly
> 
> John Freau


John:
Can you give us some idea of the duty-cycles and PPS in your
experiments? I am thinking of playing with a 4-1000A or maybe
two.

Also, does anyone have knowledge as to whether a tapered secondary
would work? I have to believe that it would, but cant see any advantage
except that I can lay my hands on a seriously long fiberglass form...
approx 27', 8 inches tapered down to four.

Any thoughts appreciated.

Randy