Re: Tube coil, level shifter madness

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

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

Dave, all,

Without staccato, I re-compared level shifter with the 2kV
secondary vs. 3.6kV without level shifter.  The sparks are 
stronger with the level shifter as would be expected, since
it's giving about 4kV, and better utilizing the xfrmer power.
Regretfully, my original observation was made too hastily.

Regarding the weaker staccato performance with the level shifter,
I have some thoughts.  I had noticed in early
staccato work using mechanical staccato, that RF 
envelopes which rose quickly, or were long in duration,
tend to cause the sparks to branch.  This is not as important
in steady (non-staccato) operation, since the sparks create
a frenzied torch of spark activity anyway, along with quickly
repeating ion trail re-ignitions.  However, for staccato 
operation, longest sparks are obtained with one straight
sword-like spark.

In earlier work with 24" level shifted staccato sparks, I was
only able to obtain the straight sword-like unbranched
sparks when using an MOT with the shunts removed.  This
type of transformer tends to produce a very narrow RF 
envelope, with perhaps a slower rise time despite the
level shifter.  I'm not sure if the rise time slows (compared to
a normal xfrmer), but I know the RF envelope is narrow.  This
combination of xfmer, level shifter, and coil design, gave 
excellent level shifted staccato sparks.

It seems that as the power is increased, it becomes more
difficult to maintain the straight sword-like sparks which are
essential for maintaining the longest lengths during pulsed
(staccato) operation.  My smaller (16") staccato coil uses an
ordinary power transformer, not an MOT.

Even without the level shifter, staccato sparks tend to
be shorter than steady sparks, unless the sparks are
straight and sword-like.  Tuning and other adjustments, as well
as the coil's design, also tend to affect the type of sparks, 
making them more or less fuzzy, branched, or pointy.  My
large 38" VTTC always gave fuzzy sparks, and this may have
been affected by the poor Q of that secondary too (maybe).
Work being done by solid state coilers will also be helpful in 
solving these kinds of questions.

Regarding the operation of my TTL staccato controller, it
seems to be triggering cleanly despite the addition of the
level shifter, since this is still a small coil.  Higher RF power
levels do tend to disrupt the TTL circuit.  When I added staccato
capability to the large 38" tube coil, I was forced to use the 555
timer based controller at the highest power levels.

In conclusion, tube coils are critical beasts, especially when
features such as level shifting with staccato, are added.  Best
results require a careful combination of components, design,
and adjustments.

John Freau