Uniflow TSG tests

["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,

As I reported recently, I had good results with a silver faced 
TSG gap, but it needed to have a fan blowing on it.  I wanted
to try varying the gap spacing, but I forgot and took the gap 
apart and built a new gap. 

I call the new gap a uniflow gap because it
has air flowing through one hollow brass electrode against a 
solid brass disc with a heatsink.  The hollow electrode is a
pipe fitting which is about 1" OD.  The solid disc is about
1.3" x 1/4" thick.  The air flow is provided by 
an old-fashioned hairdryer (blowdryer).  I'm using the same 1/8" 
tungsten rod as a trigger electrode.  Everything else is the same
as I reported recently.  My reasoning for using such a setup is, 
a) a lot of air may not be needed, b) I wanted to build a compact 
simple system.  

I simply attached a lucite plate over the hairdryer nozzle.  The
hollow electrode is mounted into the lucite plate.  I removed the
heating elements from the hairdryer because they could not be
turned off.

I first used a 1/2" spacing between the gaps, this worked, but
if I turned the phase pot to get long sparks, the TC sputtered.
I tried 9/16" and it still sputtered some.  I tried 5/8" and it was
better, and I also tried 11/16 and 3/4" spacings.  Using the latter
two spacings, I was able to adjust the phase to get full length
(40") sparks with no sputtering, or little sputtering.  The sparks
may have been a little stronger with a 5/8" spacing, but the
coil made a sputtering sound every so often while running.
With the narrow spacings, if I reduced the airflow, the coil
sputtered much worse.  With the widest spacings, I was able
to shut off the air, and the coil continued to run OK, although
it occasionally gave a bad sputter, but would tend to recover. 
Some air flow prevented this occasional stumble. 

The hollow electrode stays cool due to the air flow though it.
The heat-sinked disc gets warm.  The trigger electrode which
is air-blown, but not heat-sinked, gets very hot.  During these
tests, I ran the coil so long that the Maxwell cap got warm, and
the tuning may have changed a little, because the sparks 
emitted from more toroid areas, but the sparks were shorter.
This is usually the result of a tuning shift. 

I don't particularly like this method of triggering the gap with
a tungsten rod at the side and half-way between the main
electrodes, because the main arc srikes through
the trigger, and the trigger electrode gets hot.  The heat can
probably be cured with a heatsink.  Still, I figure that if the
arc is going to pass though the trigger tip, then I may as well
use a more massive element as the trigger.  For example, 
a 3 section hollow gap could be made, sparking end to end,
with the trigger pulse applied to the center section, and air
blown through them all.  An alternative would be to use a
triggatron or other field distortion type gap.  I have the feeling
that much needs to be done in these areas for best results.
It would seem that cooling, airflow, and quenching, are concerns
with TSG's, but that is no surprise.   These issues are usually not 
much of a concern with sync rotary gaps.  I think my tungsten
trigger electrode which gets kind of hot, is causing the slight
sputtering that I'm hearing.  It's very possible that this system
could run well without forced airflow in a properly designed TSG.
At least now the gap system with HEIC is as small as my SRSG.
If I can run without any forced air with a new gap, it may be smaller. 
I may try something with 3 heatsinked sections.

Finally as a test, I tried running the coil without the trigger by closing
up the main gap spacing some, but this gave only feeble 15"
sparks, with much motorboating.  This is to be expected because
the 0.0147uF LTR cap is too large for static gap operation with the
12/30 NST.  

For anyone who may have just joined the list, this is my TT-42
coil which can be seen at:  

  http://hometown.aol-dot-com/futuret/page3.html

(however there's nothing about the TSG there)

Cheers,
John