Re: Sword-like VTTC spark pix at my website

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

Hans, David, Bill, all,

Thanks guys for the nice comments.  A normal VTTC running on raw
AC is pulsed at 60PPS.  In this coil, I omit some positive 60Hz half
cycles of operation.  The coil may run for 1 half-cycle, then be off
off for 3 positive half cycles as an example.  I can select the number
of "off" cycles.  In the photo the coil is pulsing fast enough so
the spark appears continuous to the human eye.  I can go as low
as about 1pps or lower.  I use an SCR in the cathode circuit to
disable the oscillator for off cycles.  I call this type of pulsed operation
the "staccato mode", because of the weird machine gun like, rat-tat-
tat sound the coil makes at certain pulse rates.  

>  Looking at the pictures, I would think that the dimple in the
>  top of the e-field of the torid combined with the breakout point caused the
>  sparks to be perfectly vertical.  

I'm not sure if the toroid is needed to get this effect, but it may help some,
I'm not sure.  The breakout point is probably essential.  I used to use
a smaller metal object on top that was 3" dia, below the breakout
point and it still worked, but it still may have influenced the field 
enough.


>  Is this correct, and if so can the effect
>  be duplicated with a "conventional" coil.  If I place a breakout point on
>  the top of my small coil with a spherical topload, I get something similar,
>  but the arc usually branches a few times and waves around.  I estimate the
>  breakrate of my static gap to be about 400.  Thanks for sharing that with
>  the group.

Yes, my understanding is that a higher bps of about 400 is best for
producing these types of effects in spark gap coils.  But there will
be more wavering in a spark gap coil usually.  If I turn up the power
on this coil, a little more, it branches at top, and the whole spark
dances back and forth.  Side to side I mean.

I have a schematic for a similar coil at David Trimmel's website. 
There are also schematics for my TTL staccato controller, and
for Dave Sharpe's 555 based staccato controller.  The 555
controller is more resistant to RF interference.
There's a link from my page to his page.  In this coil, I removed
the shunts from the MOT for more power, and used Dave Sharpe's
level shifter circuit.  This is an old project, I guess I built this about
a year ago, and parts of the coil are about 8 years old.  I just wanted
to show the swordlike sparks, which many folks may have heard 
about, but not seen before.  The photo is taken with a cheap
digital camera.

John Freau

>  
>  Hans
>