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Re: Got my 6-incher going!
Original poster: Ben Buxton <bb@xxxxxxxxxx>
Tesla list wrote:
Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
Hi Ben:
That's a nice, neat coil layout your have - I tip my top-load to you ;-)
Thanks, glad it's not just me that thinks it's neat :)
1) On the NST protection circuit, replace the RF chokes with large,
ceramic-cased wire-wound resistors, 500-2000 Ohms, 50+ Watts. It has
been shown that L-C filters as you have actually make matters worse,
creating their own resonances. I suspect that's why you saw the
flashovers on the caps. I know - they won't fit into the footprint of
your chokes :-(
Ok, I will go hunting for these resistors. They will probably be too
big for my existing filter, but not to worry - I've made it modular
for that reason, and there should be enough space left on the base in
the 'filter spot'.
2) Your doorknob tank capacitor uF value sounds good, but as you said,
their 20kV rating sounds too low to be safely used with a 15kV NST. I
see that you found them to get warm after use. Do you have a
capacitance meter to see if their value drifts when warm?
I will check that, and I'll also be on the lookout for parts to make
a MMC. I'm running the SG a little smaller than I could, which I'm
hoping will keep the tank voltage a little lower to save the caps.
3) If you're using a 15/60 or 15/90 NST, you should be able to use a
much larger top load than a mixing bowl. Could it be that you just
didn't have enough primary turns to tune a larger top load?
Likely yes. I had about 66cm (almost 26") of winding on the
secondary, but I've just taken a few dozen turns off in the hope that
the frequency ups a bit, enough that my primary can get resonant with
a bigger topload. I've also lowered the secondary a little, from 4cm
to 2cm above the primary, so hopefully that will give better performance.
Thanks for your comments, and I'll keep you posted.
Ben