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Re: Building A VTTC

Original poster: FutureT@xxxxxxx In a message dated 8/21/06 4:07:27 PM Eastern Daylight Time, tesla@xxxxxxxxxx writes:

It seems that you have made a quantum leap in
the stacatto controlled VTTC that probably hasn't been pa-
ralleled since the 1990s when John Freau himself first intro-
duced the stacatto controlled VTTC, capitalizing upon the
higher output from the same power input through the
priciple of lower duty cycle firing. And I also think that it
should be pointed out to the rest of the list that this is your
very first VTTC project, so basically you've made these
advances as a VTTC beginner!

Keep up the good work,

Cameron, David,

Yes, Cameron has obtained very impressive results from his
VTTC project.

My original coil that gave the 36" sparks, and later
the one that gave 38" sparks didn't have a staccato system
attached, so they ran at 60 PPS, and drew a lot of power.
These early designs were unable to give the straight sword-like
sparks, so the sparks tended to get a lot shorter when the
staccato feature was added.  I did at some point add the
staccato feature but the sparks got shorter when the staccato
was operating.

One of my early coils gave the sword-like sparks.  In this
coil the spark length did not decrease in the staccato mode.
I could reduce the pulse rate to 1 pulse per minute, and the
sparks remained just as long.  But this was a smaller coil
which produced 20" sparks from a single 4-250A tube

When I added the staccato system to my coils in general
I didn't go back to modify the coils to take advantage of the
staccato features, so the sparks didn't get any longer, the
input power simply decreased.

When I had spoken to
Steve Ward and others, I suggested that they modify their coils
(compared to mine) by lowering the plate impedance to take
advantage of the staccato capabilities.  This is what I was planning
to do but I got involved in other work.  Also around that time I had
introduced the zero-crossing staccato circuit which helped a lot for
staccato stability.  I sent this schematic to Steve Ward and he
incorporated it into his coil and placed the schematic at his
website.  He did optimize his coils to take advantage of the
staccato, by lowering the plate impedance.  Cameron has
done that also.

Some later coils that I built did give the sword-like
sparks, so they were able to maintain their spark lengths
while running at a slower staccato pulse rate.  One later design
coil (circa Feb, 2001) produced 24" swordlike sparks in the
staccato mode and also without staccato.  This coil used two
833A tubes and was capable of running without staccato
without overheating the tubes.  It produced 24" sparks.
When running without staccato it drew 2400 watts while
producing the 24" sparks.  By using the staccato, the
power draw could be dramatically reduced depending
on the pulse rate.  For example if the coil was run at 30 PPS,
Then it drew 1200 watts (somewhere around 10amps).  If the
coil was run at 15 PPS, then it drew 600 watts (~ 5 amps).

I use a similar formula to my formula for spark gap coils,
for VTTC's without staccato.

     spark length inches = 0.5*sqrt input watts.

This formula is for VTTC's which are running at the full 60 PPS
(no staccato).  The coils will of course be much more "efficient"
in staccato mode.

As an example there is my 2nd large VTTC coil which gave the
36" sparks at around 5500 watts.  So if we take the sqrt of
5500 = 74.16.  Then multiplying this by 0.5 gives 37" which is
very close to the 36" I obtained.  I think I turned up the power
a little higher to get the 38" which I eventually obtained.

Now we can do an example with staccato mode.  Consider
my coil that gave 24" sparks both in or out of staccato mode.

without staccato:

   24.49" spark length = 0.5*sqrt 2400 watts

So it can be seen the formula is quite accurate for this coil also.

  But with staccato at 20 PPS the formula must be modified.

  24" spark length = 0.76*sqrt 1000 watts

note I used 1000 watts instead of 800 watts to allow for the
filament power for the two tubes.  In some of the calcs here
I didn't bother accounting for filament power.

  At 15 PPS:

  24" spark length = 0.86*sqrt 800 watts

I think at some particular slow pulse rate
the spark length diminished some.  I'm not sure though.
If the staccato pulse rate
is very slow, the spark will not appear continuous but will
appear pulsed when viewed by eye.  When speaking about
the efficiency of a staccato tube coil, it's best to give the
staccato pulse rate because the pulse rate has such a
dramatic effect on the power draw.  When the coil runs
at 30 PPS, the sparks look almost as full as at 60 PPS.
At 20 PPS the sparks look good too.  Each pulse rate
has it's own interesting appearance and sound.  When
the rate gets slow enough, down to 15 PPS or so, only
a single sword like spark will be seen.  This sword spark
will waver back and forth slightly as the coil runs.  This
type of spark can be seen at my website, as well as
other types of sparks.

Basically if you optimize the VTTC for staccato, then it will
not be able to run continuously without staccato.  The tubes
will overheat.  So there's a tradeoff.  Either use a high plate
impedance and permit the coil to run at the full 60 PPS
(no staccato), and limit the spark length (even with staccato
turned on).   Or use a lower plate impedance and only
run in the staccato mode at 30 PPS or less to prevent the
tube from burning up.  But longer sparks will be obtained.
The coil can be turned up to full power without staccato
for short durations, but not continuously.  Keep an eye
on the tube plate and watch for excessive redness.  Turn
down the power very quickly as needed.