2nd light (it was better)
Tonight I tried out my new double poly thickness (.12 thick total) plate
cap on my 8" coil. In the last episode the .027 uF .06" thickness plate
cap blew with about 60 volts on the variac. The new cap, now .01uF
worked like a champ at 130 volts. I'm now getting 42" sparks using
15kv-at-90mA. What a joy to behold....after 6 months of work. I don't have
a vacuum pump so the cap was assembled under transformer oil to
eliminate air bubbles, what a mess, but it worked.
The primary was re-tuned for the new cap by measuring the resonant freq.
of the secondary/toroid using a signal generator, resistor in series,
and a Fluke 87 "true RMS multimeter". The peak current draw through the
resistor came in at 167.9 KHz and was quite sharp. I could not get an
accurate Q measurement. I'm guessing 100 to 500. Sound reasonable?? The
measurement was very sensitive to me walking near the coil as you would
expect. The measured L of the secondary was 28.5 mH, translating into a
Ctotal of ~33 pF (toroid size 7"x30"). For a reference point, this was
somewhat off from the calculated numbers from Ed Sonderman's Tesla
designer which calculated Ctotal= 43 pF.
I recalculated the primary circuit and needed ~2 more turns to make 88
uH or 168 KHz. The coil came right up with the 42" sparks.
Now for the fine tuning!!