Re: More tube coil stuff (Carl Willis)...

[cwillis-at-guilford.edu (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

>>>Are you using a very long time constant in the grid leak network to
>>>create pulsed operation (grid blocking)... what I used to call the
>>>sputter mode?  I no longer use such a mode.

Yep, I use the sputter setup still- 40 kOHM, ~.002 microfarad.  That is
indeed a big RC.  I can select my sputter frequency by selecting more or
fewer parallel capacitors for C.  I get characteristics of disruptive coils
when the sputter frequency is low (capacitance high, like .004).  There is
a lot of bluish-white corona and white thin streamers from my breakout
point.  With less capacitance, I get tube-coil-style fiery arcs and
discharge.  These get thicker and shorter (.0001 microfarad) as I keep
increasing capacitance and the coil moves towards more of a CW oscillator.
I like to run somewhere in the middle where the arc is thin but still
substantial and violety-orange.  this is also where I get the longest
sparks with my sputter arrangement.

>>>Are you sure the coil is tuned very precisely?  I would expect at least
>>>a 19" discharge using the nail.  Streamers should be somewhat straight
>>>not too fuzzy.  Also grid feedback, grid leak resistance, etc, are all
touchy
>>>adjustments.  I never run without the breakout point, except at low powers.

It is capable of being tuned precisely (with a transmitting air variable
submersed in mineral oil in parallel with an MMC), but the tuning that
works well for one type of discharge (20" horizontal arcs out to my hand
from a point) does poorly for the other (brush discharges). I can make a
brush about 20" long come off horizontally from the nail when I retune to a
higher primary frequency.  Its multiple branches are long and thin, not
fuzzy, straight, pretty much as you describe.  They will hit my hand if it
is in range, just like the brush hitting Robert W. Stephens' ground
terminal in his pictures, but they act like "they don't care" if your hand
is there or not- they get no longer to reach out to it and they don't bend
around to hit it.  They are more or less straight, and if they are already
headed towards the conductor they hit it. Whereas, with the tuning I like,
the brush is small but when my hand comes out towards the coil it lengthens
and goes for contact, forming a single streamer. 

I think tube coils are extrememly sensitive to tuning as opposed to
disruptive coils. Brushes and streamers are going to have different
impedances, and maybe this is reflected by having to retune the coil to get
better results with one or the other.

>>>I never run without the breakout point, except at low powers.<<<

I avoid this also, because it corresponds with flashover in my tube.  Makes
a spattering, barely visible breakout all over the toroid and the top lead
of the secondary, usually accompanied by the occasional "ping!" from the
tube. When it is all tuned up to do this, I can't bring metal or hands
toward the coil without detuning it enough that the breakout stops.  I run
at low power with no breakout (variac at 70-80 volts) to light up discharge
tubes and play with the radiation field.

>>>I find a fine tuning adjustment range over which the spark length will
>>>remain the same, but towards the sides of which will reduce the tube
>>>plate redness.

My plate does not get red to any extent at all, perhaps because of the
low-duty cycle of sputter mode.  It does redden up considerably as grid
leak RC is lowered towards CW mode, and when it is CW (I haven't run it
like this for a couple years)and it is being heavily loaded by discharges,
the plate gets dangerously orange hot.  This is why I made a heatsink that
I still use for the plate pin out of aluminum to protect the seal, though
it is completely unnecessary and unsightly.


>>>You may remember my recent disappointing VT-27 VTTC experimental
>>>results.

I have missed out on a lot of list activity this past summer because it
takes eons for the modem at home to download the 100's of posts (literally)
this list generates.  I'd like to know what you tried to do and what
happened.  You can direct me to the threads in the archives and I will read
about it. 

I have another question for John or anyone else who wants to add their two
cents.  There was a small synchronous motor in the physics dep't trash
today (still works though), which has a disk on its axle with a little
cutout on its circumference that momentarily closes a 450-volt, 15 A switch
every time the axle makes a complete rotation.  I don't know what this
arrangement was for.  But I have an idea about where to use it- as a
cathode grounder for a staccato mode operation in the tube coil. I know
nothing about SRSG's, but I wanted to be able to synchronize the switch-on
pulse with the positive AC wave peak.  Comments, suggestions?  I need them!

Thanks,

Carl