New project status
I finally got everything put together Saturday morning and got this project
lit up. It works great! This coil makes the first one I built (in high
school many years ago) look like a toy. This thing makes serious sparks -
and a hell of a lot of noise. I think I should wear hearing protection - if
my hearing wasn't already shot.
Here's the details:
Secondary 27.6" long, 6.0" dia, #22 mgnet wire, measures 32 milliheneries.
Primary 14 turns 3/8" copper tubing wound at 30 degrees on a plastic form.
8.0" dia at base, 27.5" dia at top measures 82 microheneries.
Discharger is 14" dia x 4.0" thick made of styrofoam covered with foil tape.
Tank capacitor #1 is .0186 mfd, # 2 is .0178 mfd.
Bypass cap # 1 is 698 pf, # 2 is 675 pf.
RF chokes are 650 to 700 microheneries.
Running at this time with two 12kv 30ma transformers in parallel.
I ran it with the two tank capacitors in series tapped at 14 turns until
Sunday afternoon at increasing power levels. I did get it up to full power
finally. I never did see more than 4 small air bubbles come up in one
capacitor and none in the other. It seems to tune with the two capacitors in
series right at 14 turns. With one capacitor it seems to tune at 10 turns.
I calculate the frequency to be the same at these two points - exactly 185
khz. I don't seem to be able to tune it within a turn (i.e. 9.5 or 10.25
turns) although I can tell the difference between say 9 turns and 10 or 11.
I do seem to get more power out of it with one cap tapped at 10 turns.
This brings up a point that I have seen discussed. I calculate the quarter
wave frequency of the secondary to be 150 khz. This must be the frequency
that will produce the highest voltage at the top of the coil. Does the
discharger and the loading of the primary actually bring the primary
frequency down by 35 khz to 150 khz?
I noticed that I can increase the discharge length by sitting a 10.0" dia x
2.0 " tall stainless steel pan on top of the discharger. Which I imagine
tells me the discharger is too small, correct? When I do this, it forces all
the discharges to go downward - none off the top -- curious. Can you tell
me why? At full power in this configuration I get strikes down into the
primary causing very loud pops which in turn causes the safety gap to fire,
and of course I immediately turn the power down. I assume these pops
indicate the primary is being shorted by the ionized air. I can't figure out
how the strikes are getting past my strike rail. It is also copper tubing
mounted about .75" above the last turn on the primary. I only have the
strike rail grounded to the RF ground with a #12 copper wire. Is this the
problem? I can raise the discharger by a few more inches but I don't think
this will help much.
By the way, what do you do with the metal case on the cylindrical spark gaps?
Because of its close proximity to the AC line (inside the motor) I did not
want to connect it to RF ground and I did not want to connect it to AC line
ground either so I finally just built a shield over it and connected it to RF
ground. What do you do?
Talk to you later, Ed Sonderman