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3-1000z VTTC - Record breaking final run

Original poster: "Ross Overstreet by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ross-o-at-mindspring-dot-com>

Hi Guys,

I set a new arc length record with my 3-1000z VTTC.  I managed very solid,
repeatable, multiple arc per second hits to a ground rod located 28 inches
above my breakout point.  I discovered that a toroid on top of the VTTC
provides field shaping and forces the arcs to be more vertical.  I managed
4-6 more inches with the toroid but they weren't nearly as pretty as the
"bushy" arcs that I get without the toroid.  I got these results by letting
the VTTC cruise at its max plate ratings of 700ma & 3KV and then surging the
variac up to about 5+KV, 1+A plate.

The coil started tripping the breaker after the first couple of tries doing
this.  I noticed thermal damage to the side of the plate and knew that the
tube was pretty much history.  After a breaker-tripping episode, I would
have to turn the power up really high to melt the short between the plate
and grid so I could run it again!  I didn't want to miss out on documenting
the 28" arcs (or tube death) so I grabbed my camera and got some stills and
about 30s of video.  I even managed to get the VTTCs final run on video
along with a massive flash over inside the tube!

I hate the tube is dead but I learned a great deal by abusing it.  I now
have a data point as to what is "too much" for a tube.  I also have a good
understanding of "best practices" when building a VTTC of the conventional
configuration.  Remember that is the first time I've ever built anything
with a tube in it!  (or even seen a tube up close, for that matter)

I feel that my knowledge is still deficient in understanding exactly what is
going on in the grid circuit.  I hope to document the waveforms in this
mysterious place as soon as my fiberprobes are complete and I find another
tube.  I'm also quite disappointed at the prospects of instrument tuning a
VTTC.  I had lots of room to adjust L(p) and C(p) and never really found a
point at which performance would abruptly drop off on either side.  The
values that I found with my scope and signal generator didn't seem to agree
with what the VTTC preferred.  There are so many variables in these machines
that finding the optimal tuning point can quickly turn into a seeming
impossible job.  Any advice in this area will be appreciated.

Pics and video of the final run can be found on my site.  Thank You to Terry
for hosting my large video clips.