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Re: [TCML] LTR/STR
particularly with beginners, folks find that the wider they open their
gaps, the better performance becomes, so setting the gap width PROPERLY is
often not done.
I do have the safety gap set according to how it's been explained here, no
caps attached, and I even set it close enough that it starts to fire around
90, 95% power from the variac. I'd rather be conservative in this situation.
Now to your situation. With a 15/60 NST, the mains-resonant cap would be
.01uF, or 10 nF. So your 4 nF cap is significantly STR. That's OK as far
as avoiding mains-resonance, but it's limiting the performance of your coil.
I have found that the optimum cap size for a 15/60 NST is .02uF. Spark
performance correlates with "bang size", or the amount of energy that the
cap discharges each time the gap fires. This energy is calculated as 0.5 *
C * Vgap * Vgap. The higher the capacitance, the bigger the bang.
That would explain my noticable jump in performance. I started out with 2nf,
and only recently added more to get me to 4nf. Then I doubled the size of my
toroid (dryer duct type with foil tape), sparks got better. THEN, I
completely rebuilt my spark gap(s) from scratch. My original attempt had the
components mounted on a wood base. Yeah, yeah, I know now. Wood bad, plastic
good.
If you are planning to downsize to a MOT (not what I would call table-top
sized!), you will need an even larger nF cap size, since the voltage is much
less. For my table-top coil using a 4/20 NST, I use a 25nF cap. Are you
locked into the 4 nF cap?
I initially thought mot for the lower voltage, but maybe an obit would be
more appropriate. However, based on what you're telling me re: my current
coil, I think I still have a lot of room for improvement. Re: capacitance;
no, I'm not necessarily locked in at 4nf. I think before I downsize, I'm
going to tweak my 4" some more, sounds like I have room to grow there. So,
in a nutshell; less voltage requires more capacitance. And, as long as the
safety gap is set properly, capacitance is less of an issue, at least as far
as not frying components. Much more improvement, and I'll outgrow my little
space in the basement, but that's an "inconvenience" I plan to strive for!
Thank you very much Gary, I'll let everyone know how things work out,
Neal.
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