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[TCML] Terry Filter Problem
I constructed a Terry Filter for protection on my NST, and have been having
some weird issues with it. The the first time I ran, I had the 120v input
for the NST going through a dimmer switch like this one:
When power ran through the coil with filter, I left out the caps to test the
safety gap on the filter. It only made a low humming sound from the NST, no
sparks, no nothing. After some toying with the filter connections I reduced
the spark gap distance/safety gap distance to only a few mm of air. It
seemed to be working. I started to increase the spark gap distance back to
the NST's "unstressed" capacity, and the Terry Filter made a cracking blue
arc around a cap. I also noted that only one safety gap seemed to be
firing, the other did nothing regardless of its spacing. I wanted to
pinpoint where this arc occurred, and after running it again, the first cap
of each string exploded on the side closest to the NST hot lines! "Not a
big deal, I lost two $1 caps, let's try again tomorrow."
I decided it was an isolation problem and hot glued down thin plastic sheets
all over the board where arcs might break out between components. Not a
great idea I suppose, but it worked on my cap bank.
So I give it another go, this time with only 5 caps in each sting instead of
the original 6. With very little amounts of air to break down, it works
fine, but once I start increasing distances to what the coil should be
running at, I get this arc in the same place, on the same string of my
I'll post pictures tomorrow when I can borrow a camera. What kind of
problem does it sound like? My friend thought is was arcing to the ground
wire....could be, my ground line is running down the center of the PC board,
lying directly on it.
The Terry filter's "RF ground" line is running to the RF ground, the
filter's "NST ground" line is unconnected because the NST case is also
ground to the RF ground.
The holes on my PC board are copper one one side, but so are the holes on my
cap bank, and I never had arcing problems there.
I'm pretty lost here, and if I don't wanna risk killing my NST over
anything, so any advice will be helpful. Pictures will be coming soon.
Thanks for the help,
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