New TSG results

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

Hello all,

Using a modified setup, I had excellent results using the STSG
today on my TT-42 TC.  In a direct comparison with the sync rotary,
it was hard to tell the difference.  Both seemed to hit the 40" 
measuring wire with equal ease.  The rotary sparks may have been 
a little stronger and bushier, but it was subjective.  There was not a
clear-cut nor easy to see difference.  I have a lot of burned spots
on the secondary from previous TSG tests, so there may be a
short in the secondary, but I'm not sure.  When I set the 
measuring wire at 42" the rotary setup spark reached the wire
one time, the TSG sparks did not.  There are probably greater
losses in such a long gap arc, but it doesn't seem to affect
the coil's spark streamer length very much.  My gap spacing is
about 9/16".  I didn't try adjusting it differently, but it's possible
I may be able to adjust it a little closer.  

I had to use a small house fan blowing on the main single static
triggered gap to prevent power arcing.  Without the fan, the coil
sputtered and sparks were unsteady and weak.  Even using
the fan, the coil sputtered occasionally, so it may have needed
a little more air flow.  I'm still using the heavy copper electrodes
with thick silver faces as the main static gap electrodes.  The
spark gap is very bright and gives a white-hot arc.

I built, and am now using John Tebb's phase controller circuit design
which uses a 555 timer, a zero crossing detector, a few transistors,
and some other parts.  At first I was not getting a powerful enough
spark from the HEIC, but it turns out that the microwave oven diode
I was using in place of the damper diode was reducing the HEIC's
output.  I didn't try using a different diode, rather I just ran the
circuit without the diode for these tests.   The HEIC gives about a
9/16" maximum length spark with my setup.  I used a rather
small power transformer but it seems adequate.  I used about
1.3 ohms in series with the HEIC.  An 18awg 6 foot zipcord connects
the  controller to the HEIC.  The controller circuit is built onto a
3.25" x 5" perfboard, which is in turn mounted onto a 6" x 8" wooden
base which also holds the small power transformer and the phase
control pot and knob.  All the parts run cool or just slightly warm.
Only the transformer, the input power rectifier (I used half of a
bridge), the HEIC series resistors, and the H.O.T. run slightly
warm.  The H.O.T. is mounted onto a nice heatsink.  John's
design performed excellently overall (thanks John!).

For best results, the phase adjustment is quite critical.  If turned
one way, the coil stops firing, if turned the other way, the coil
sputters.  Before when I used the lamp dimmer type controller, I didn't
have quite enough phase range as I suspected.  The limited
phase range prevented me from turning up the coil to full power.
Now, with the John Tebbs controller, I'm able to turn up the
variac all the way to 140 volts.  I didn't monitor the gap firing 
with a scope, but there should not be much or any jitter.   

In future work, I plan to monitor the gap firing, measure the
quench time, and build a spark gap similar to Gary Lau's vortex
gap, to use with the trigger electrode.  I want to try to keep everything
as compact as possible.  Finally, a variable break-rate TSG
would be an interesting project.

The STSG is clearly an excellent gap choice for many coiling
situations.  For small coils, no air flow is needed, so the gap
can be quite compact.  The use of a triggered multiple gap
also may eliminate the need for cooling/quenching airflow, up
to some particular power level.  

Cheers,
John