RE: half filter?? and what all I need before primary circuit

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Original poster: "Godfrey Loudner" <ggreen@xxxxxxxx>

Hello Gary

Indeed, the measure of success in depotting a NST is patience and
delicacy. The only evidence I have is my construction of two neon like
transformers. I started with two large identical filament transformers
for x-ray machines by stripping off the filament windings, but leaving
the 240 volt primary windings intact. The cores are rectangular with the
primaries on the bottom legs. Two plastic containers were constructed so
that the top legs could slide down   plastic channels. Otherwise, the
cores would not come into contact with the oil. In each transformer I
installed two HV coils from dental x-ray transformers. All the HV coils
are identical. In each transformer, the two HV coils are connected in
series and isolated from the core. For oil expansion, a small hole was
drilled on top of each transformer, dabbed with Vaseline, and a small
piece of plastic pressed on. After filling with transformers oil, I was
lucky to have no leaks. The primaries were connected in parallel and the
HV sides in series, with center grounding to an earth rod. The power
supply consisted of a heavy variac and a 120/240V shop transformer. With
pointed electrodes set six inches apart, the gap would break down at
less 100V from the variac. The sparks were loud and white. With an arc
established, the variac could be pushed up to 140V, where the white
sparks become laced with flame and more quiet. With the outfit working,
I decided to lock the gap at six inches. I ran this outfit a lot with no
breakdown. Because the primary and secondary windings are on different
legs, the transformers are current limited. However, at a certain
voltage level, the oil begins to sort of quake and looks very disturbed.
So I now think it was a mistake not to submerge the cores under
oil---well its working for now.

Godfrey Loudner





That's sort of like asking if you could run the marathon faster if you
had a heart transplant.  Depotting an NST is a substantial, unpleasant,
and messy project, and success is not guaranteed.  The secondary
windings are very fragile and easy to damage, and I'd not recommend
attempting it unless the NST was otherwise a lost cause and
irreplaceable.  Mine was a 15/60 - useless in its present state and
fairly precious.  Had it been a 15/30 I probably would have just tossed
it and found another.

I would guess that an oil-insulated NST would be more robust than an
old, used, asphalt-insulated unit, particularly since the asphalt tends
to crack with age, but I have no data to back that up.

Regards, Gary Lau
MA, USA