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Re: [TCML] poor coil performance again- help!



Sorry I sound so depressing, but the more I looked at it, the more trouble I realized. I've been down your road with a small coil a while back. It sucked! I had a couple hundred more turns than yours, but the coil was even smaller. Primary was fixed at 4 turns and I tried it with a 7.5kV 20mA NST. I eventually installed a 12/30 to force some power into the coil, but it was still dismal. I ended up giving it to a buddy. He thought if he wound another layer of turns on the secondary he could get it working better. Too bad he didn't ask me first. Oh well.

If you want a good performing coil, then you need to design with the following in mind:
1) 900 to 1300 turns.
2) H/D ratio between 4 and 5.
3) A coil diameter of 4" or larger.
3) Good static gap with lots of air cooling or srsg.
4) A transformer about 12kV or near with at least 60mA.
5) An MMC cap designed for LTR operation (it's value) for the static gap or srsg (and those values are different).
6) A primary that tunes between 10 and 15 turns.
7) A toroid sized appropriately for breakout, loading size, and as smooth as you can get it.

The above are just some very basic preferences. Your coil hits #2 and slightly #3.

I'm sure if you worked with the coil, that you can get it performing better, but there is a limit with the coil and that's what I'm trying to get across. I guess if it were me trying to get the coil working better, I would ditch the bottle caps and build an MMC with a larger cap size. But this would require a larger turn primary, so I would have to build that also. I would also upgrade the NST and install a toroid top load which will help lower the frequency (which helps in other areas).

It of course takes work, time, and money to make a decent coil. It's not rocket science but there are pit falls to watch out for and experience is the best teacher.

Take care,
Bart
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