Ed,
I am not currently metering the grid (or plate) current
in my setup, so I cannot answer the current question. I
am really pretty dumb on vacuum tube coils and this one
was based loosely on Steve Ward's 833A VTTC that
is supposed to yield 22" sparks in stacatto mode. The
only difference is that I am using 2 seriesed MOTs
through the voltage doubler circuit, just like Cameron
Prince did on his. As a matter of fact it was my perso-
nal viewing of Cameron's coil's output that convinced
me to take on this as my first VTTC project. Anyway,
I have used two or three different used 833As and always
got about the same output. However, I decided to or-
der a new (Taylor) 833C because Cameron had pur-
chased a used one on eBay and had reported good
results, mainly the plate stays cooler at a given power
level. However, when I tried my new 833C tube in
my circuit, it had a very limited spark length output and
the spark output would not increase beyond about 40%
on the variac knob but would instead start to take on
a "crackly" sound. BTW, the output at this point is only
about a pitiful 6 to 8", in continuous mode! Further ramp-
ing up of the variac beyond this point does not increase the
spark length any further but it is apparent that there is more
plate current as the graphite plate will begin to take on a
glow. BTW, the output sparks will continue to grow pretty
well linearly with increase in the input via twisting up the
variac knob when using the old 833A until I can't really
turn it up much past 60% on the variac knob due to ex-
cessive plate glow (in continous mode), but the spark length
at this point is around 16 to 20". Any more suggestions, I'm
all ears :^)
--
David Rieben