sword like sparks, new info???

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Original poster: "Steven Ward by way of Terry Fritz <teslalist-at-qwest-dot-net>" <srward16-at-hotmail-dot-com>

Hi All,

Since Dan was getting such awesome output from his dual 833A VTTC, it 
sparked my interest in my dual 833A VTTC ;)

So today i played around with some stuff.  I found something that may be 
useful in determining what causes the swordlike appearance.  Heres what i 
found.  The smaller the voltage doubler capacitance, the lower the voltage 
input needed to achieve SP (sword sparks), but also, the lower voltage 
needed to ruin the effect!  This is going by input voltage from the variac 
(i dont know what it happening in the tank circuit).  With 2 caps in 
parallel, the SP was ruined at about 80% input. Sparks were thin compared 
the the normal ones and only 20".  Then, with 3 caps, i needed about 83% 
input with thicker sparksthat were maybe the same lenght or slightly 
longer.  Then 4 caps, about 90% and maybe 21" sparks.  Finally 5 caps, 100% 
needed, and 24"+ sparks ;)  At this point the sparks looked about 2X the 
brightness as with 2 caps, and were hitting 24" several times a second.  I 
also noticed that each trial needed slightly different grid feedback levels 
(maybe +/- .5" of sliding the grid coil above the primary).

So, it seems that my coil (and Dans, since he noticed that the SP were 
ruined at too high of a setting) needs a special voltage to current ratio 
to create the proper spark formation.  I think the voltage plays the role 
of the correct spark formation, and the current gives it its lenght and 
brightness.  This is also assuming that, less voltage doubler capacitance 
requires less voltage from the MOT to reach this ideal voltage level.
Meaning, a large cap will produce less voltage output since it loads the 
transformer down more when charging a larger cap.

Ok, but now i need to know why this voltage is causing the SP to be ruined.
Could it have something to do with the grid feedback?  ie, too much is 
produced?  I would say no.  It seems that if i reduced the grid feedback 
(raising the grid coil further from the primary) did nothing but make the 
sparks worse.  Maybe, when the voltage into the primary is too high, the 
sparks have a tendancy to branch since they have enough voltage TO branch?
This is what im thinking.  It makes sense!  When the sparks branch, they 
seem to form 2 or 3 sword like branches, each about 12-18" in length.  All 
of those streamers individually would add up to one awesome spark!

So, as of now, im thinking that more current and just the right amount of 
voltage is needed to achieve the maximum sword like sparks.  Now its time 
to log some precise data ;) I plan on taking lots of pics of the RF 
envelope at various styles of output.  I think this would be helpful.  I 
wish i had some HV probes to see what the grid feedback, and primary coil 
are seeing.

Im sure John Freau has something to say about this ;)

Steve Ward.