TSG update

["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, 

I did some more tests using the TSG.  I wanted to test the 
arrangement that Weazle mentioned of grounding the HEIC 
core, and using a capacitor from the HV terminal to the 
trigger electrode.  I tried this, but the safety gap still fired 
even with the TC not running.  The spark is seeking ground 
though the safety gaps.  It seems that most folks use a 
Terry filter and the filter gives enough blocking to the 
pulse so the safety gaps don't fire.  I never use any kind of 
protective filters on my coils, I just use safety gaps.  It's a 
good idea to use a filter though, because the RF is not good 
for the NST windings, although I've had no failures.  Coilers 
who don't use filters need to consider this issue of the safety 
gaps firing.  I find that most NST failures result from setting 
static gaps too wide, so they fire unsteadily.  I generally use 
a sync rotary rather than a static gap because of the great 
smoothness and performance of the sync rotary. 

To solve the issue of the safety gaps firing using the TSG, 
I connect the HV terminal directly to the trigger electrode, 
I ground the HEIC core, and I connect a capacitor from 
the HEIC core to each electrode of the main spark gap. 
This lets the trigger electrode "see" ground though these 
caps, and it seems to work OK.  The safety gaps don't fire. 

I'm able to turn the power up to about 116 volts on the variac, higher 
than that, the coil runs unsteadily.  I'm not sure if there's a quenching 
problem, a phase range problem, a jitter problem, or gap adjustment 
problem.  As a test, I shut off the fan, and then I could only turn the 
variac up to about 113 volts before the unsteadiness began, 
and the sparks were shorter.  So it's quite possible that 
quenching is becoming an issue.  I think I need more phase range 
too.  I tried various gap spacings, and I couldn't really get it to 
work any better than it is now.  This TT-42 coil may draw 
almost 800 watts or so, and I think some folks have said they 
needed a good airflow at 800 watts.  This suggests that it may 
not be possible to build a TSG which quenches well at 800 
watts or higher without special techniques, such as using a 
multiple gap, an air blast, or certain electrode materials.  I'm 
using silver gaps which may not be the best at these powers. 
If the TSG needs such extra parts at high powers, it may no 
longer be compact or simple to build.  I can't help but believe 
that the ferocious brightness of the TSG spark, along with the 
purported loudness, signify substantial gap losses compared 
to a sync rotary.  A sync rotary gives a much more muted gap 
arc.  As it is, my rotary is a lot smaller and simpler 
than my combined TSG setup.  Rotaries are very simple devices, 
but the required machining to build them scares off some folks.   
Nevertheless, until I obtain adequate quenching, and phase range, 
I can't complete my comparison of TSG vs. sync rotary.  I may 
need to build the John Tebbs 555 timer based circuit so i can 
get enough phase range, and cure any possible jitter problems.   

Cheers, 
John