Re: sword like sparks, new info???

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

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

Another thought . . .

Could the field produced at the top of the coil (produced by whatever RF
envelope is present) greatly affect the direction and appearance (swordlike)
of the arcs themselves??  I was wondering this because basically no matter
how I orient my coil (I tried all directions but upside down due to obvious
reasons), the sword like
arcs always shot out in the direction of the secondary . . .

Hmmm . . . .

The Captain




 > 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.
 >
 >
 >
 >
 >