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Re: [TCML] frailty of NSTs
NSTs are engineered/designed to produce a high potential long enough to
ionize gas in the neon tubes. This process usually occurs in a few
milliseconds, then the output voltage drops under the tube's load to around
500 volts or less. At this point the NST becomes a constant current source
delivering 30 or 60 mA to keep the plasma ionized and conductive.
NSTs operated in their intended service mode work fine in a tar-like
insulation. Put some kickback RF into this type of insulation and it forms
"spiderwebs of hv tracking" all across the secondary windings. These small
streamers find a ground, and then the insulation quickly breaks down as the
more powerful 60 Hz currents begin flowing across this lower resistance
NSTs were never designed to hold 12,000 Volts for several minutes at a time,
e.g., the length of time your coil is running.
NSTs were also never designed to be used in resonant circuits that might
produce overpotentials. This is why some "kickback" protection is required
in all NST powered Tesla oscillator circuits.
No, sec wire size is not the problem. In many cases experimenters have
removed the shunts and operated NSTs at 200-250 mA with no problems. I do
this and definitely immerse them in transformer oil for better insulation
and cooling. They handle the higher currents without problems. It's
the voltage that kills them.
On Sun, Mar 23, 2008 at 11:30 AM, mark olson <kc5gym@xxxxxxx> wrote:
> Hello all,
> Happy Easter to those who celebrate.
> What is it about NSTs that makes them so fragile? I suspect it is the
> current through a secondary wound with
> inadequate wire size.
> I have a couple of E I laminate core transformers 1.25 inches wide by 3
> inch stack, six by seven o.d.
> that I am considering rewinding. I believe that winding separate primary
> and secondary would be better
> than secondary over primary or even primary over secondary.
> Any thoughts on this?
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