Hi Bart,
The SISG coil seems to like a "large" tank cap. When run on the 3
MOT's, I can set the tank cap up for 200nF. Running on the pole xmfr, I
configure the cap for 133nF @ 30KV. I’m gonna buy a bunch of 942C's and
add another 100nF to it. I watch the firing with an O'scope, and then
tune the primary accordingly. With the SISG coil, the proper tune point
is VERY easy to see. The firing voltage is approximately 26KV peak to
peak. Of course the 1st fire pulse is 14.4KV(16 modules), the ring down
pulses are of lesser voltage. I have the SISG modules in a plexi duct
with a fan. They run hot as hell. I am VERY careful to use the fan as a
warning. If I hear the fan, I don't touch. I have an IR thermometer to
check the transistors. The 1M resistors across the sidacs discharge the
tank cap after 60 seconds or so. I monitored the high voltage for the
first few runs. I also use a check list to be sure the SISG coil won't
pop me.
I have a large VTTC powered by a 7.2KV pole xmfr and a 3CX3000F1
tube. The secondary is 6.25" X 32" wound with #28 wire. The pole xmfr is
FW rectified (same rectifier as the SISG) so the VTTC runs on 120Hz
full-wave. I consider the Toob coil much safer, even though I have to be
careful switching the high voltage off. The switch is close to the
"action". It makes noise and corona at almost any high voltage setting.
The big VTTC has a spark length of 36-40 inches, while drawing 60A. I
can crank it a bit higher, but I get external flashover on the tube. 1st
time it happened, I almost wet myself. Sounded like a Cherry bomb.
I like playing with the SISG coil. It's quite a bit of fun to
observe the sparks, without that dazzling light from the SG. I have been
setting the variac on the SISG coil to 220-230V. I may be able to add 1
or 2 more modules and still have necessary voltage to fire. 18 modules
will require 16.2KV to fire. We'll see. Later, James