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Pulsed tube TC work
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