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Re: An easier way to revive an NST?

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Garry,

I think Gary Weaver (?) used to recommend simply heating the NST tar till it
was molten and then letting it recool to fill up such cracks.  He did this with
his NSTs and always got excellent life from them.  The fact the many
manufacturers are trying other things besides tar also suggests that cracking
is a big problem.  I guess the only reason they use tar is because it usually
works and it is really cheap.

I think some people have also tried adding oil to the hot tar to help it stay
softer and also avoid cracking.

So it sounds like you are on the right track here.



At 12:57 PM 5/20/2001 -0700, you wrote: 
> I have gone thought several NST's that were shorted and I note one thing that
> seems to be in common with all of them.
> Cracks in the tar. This leads me to suspect that it isn't just the presence
> of tar that is the culprit but cracks in the tar that allow a channel of air
> to become ionized and conduct a spark that burns a carbon trail in the tar -
> shorting the NST.
> I also note that the unpotted NST I am using that is inside a mineral oil
> bath had copious amounts of tar in between the windings. The mineral oil is
> quite black and yet the NST works like a champ with no signs of trouble.
> I have an idea I am going to try if I ever need another NST. I think that
> this might be a very long time at the rate things are going with the NST
> lasting so long and having a spare too so maybe someone out there can give
> this a try and put an nst through a workover to see if this idea works
> revives and prevents further breakdown. ....
> The idea ... Melt most all the tar you can get out of the NST, leaving the
> NST core inside the case. If successful, the carbon track will be melted
> away. Then pour mineral oil inside the NST, replace the top and seal it up
> with silicone seal and just try to get it to break down again.
> What I suspect will be found is that the oil will soften the tar helping to
> prevent further cracks and the oil will fill any cracks as they form and you
> will not be able to cause another short in the NST.
> You see, I have this unpotted one, and it apparrently had plenty of tar left
> in between the layers of the secondary and yet, it never has shorted. 
> Could someone try this on one of their dead NST's and let me know the
> results?
> If this pans out, there will be no more need to depot and fuss with a lot of
> messy tar and solvents, no more dinging of windings, no more NST's destroyed
> because I soaked them so long in mineral oil that the paper layers in the
> secondaries disintegrated. If this works as I expect, it will be the best
> thing since sliced bread.