Re: Repotting NSTs

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Scott Kraus <plymouth_4406@xxxxxxxxx>

Jonathan,

I have unpotted several NST's and several checked out as you found 
with the good side reading higher resistance than the bad side. After 
unpotting I found that the bad winding seemed to have overheated and 
ruined the insulation on the wire in the center of each layer that I 
examined. These were obtained from neon sign shops and had failed 
most likely under normal service so heat may have been more of a 
factor than in your case. The ones I fixed I was able to take two 
transformers and make one good one but a 120ma. would be hard to find.

Scott


Tesla list <tesla@xxxxxxxxxx> wrote:
Original poster: "Jonathan Peakall"

Hi All,

Well, I finally destroyed an NST. I wouldn't worry about it, except that it
is a 12/120, and the 120's are rare. I was using it to power a Marx bank. I
get full spark from one side and a wimpy spark from the other. The good side
reades a few ohms higher than the bad side, which is probably how it was
before. This makes me believe that the cause is carbon tracking.

So yesterday I melted the tar. It was quite easy. I used an old metal pot,
the kind used for canning. I cut a hole in the side large enough to fit the
barrel of my heat gun in there. Put some old clothes on and around the pot
for insulation. Took a few hours to melt the tar, but very little stink and
low chance of fire. Anyway...

I let it cool, and while it seems a little improved, it is not fixed. So I
have to empty the NST of tar, use solvent to clean it, and then I want to
repot it. I don't want to use oil. This NST is going to get moved around,
going to school and so on. I don't want to be dragging around a leaky oily
mess.

I have concenrns about re-using the tar. First, it will be hard to keep it
perfectly clean. And then there is going to be some loss of tar, so even if
I tried to save it I might not have enough. Anyone know where to buy such
tar?

I am assuming that the NST must be potted. Can they be run dry?

Many thanks,

Jonathan
www.madlabs.info