Re: More destroyed NST's How do I remove stubborn tar?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steve Rosenthal by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sdrosen-at-cwia-dot-com>

What brand did you say those were? Are they identical models? Document this,
it may be valuable information.

____________________________________________________________________________
____
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, January 17, 2001 5:03 PM
Subject: More destroyed NST's How do I remove stubborn tar?


> Original poster: "Garry Freemyer by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <Garry-at-NDFC-dot-com>
>
> Well, today I destroyed my fifth NST out of six tries and I am at whits
end
> on how to prevent this nasty problem from recurring over and over and I
want
> to ask people out there a few questions.
>
> The problem - When I try to disolve the tar off of an NST I continually
run
> into the same problem where about 80% of the tar disolves redily but about
> 20% of it is like hardened concrete and these mounds of tar are so
resistant
> to solvents, so hard to remove that the toothbrush I was using to brush
away
> the tar was literally wearing through the cover of the windings exposing
the
> wires below which allowed the wires to be swept to and fro until I had a
big
> mass of snapped and broken wires that were being obscured by the tar
> blackened solvent. I was just scrubbing at a stubborn wad of tar on the
> windings and suddenly, I see a busted wire sticking out.
>
> What I was wondering is has anyone else had reasonable success in
depotting
> or are we all failing misereably when trying to depot an NST? I have
> recieved a number of emails from people who have told me that their
attempts
> at depotting were just as abysmal. I suspect a few are embarrassed to say
> they failed and so they don't say anything, thus giving the false
impression
> that depotting is simple, easy and has a high degree of success.
>
> As I recall, there are lots of sites describing depotting as being very
easy
> and simple to do successfully.
>
> Claim: One book I have says just three days of soaking in mineral spirits,

> kerosene or gasoline removes all traces of tar or that what is left is
> easily removed by bit of solvent and a toothbrush. The book also says it
> take only a gallon to clean an NST. I have heard this claim from several
> sources.
>
> My own experience is FAR from anything like this. I spent SIX WEEKS
soaking
> a transformer in mineral oil. I consumed 7 gallons of the stuff and the
NST
> still was so full of tar in the windings that immersing it in a fresh
gallon
> of solvent reminded me of the sight of an octopus spewing "Ink" all over
the
> place. The entire gallon was instantly black as night.
>
> For those who have tried depotting, what is your experience? How many
> gallons did you go through to clean an NST?
>
> Many sources say one can melt out the core and most of the tar by putting
it
> into an oven at 200 degrees. Mine sat there for hours at 250 degrees and
it
> was still hard as a rock. Nothing even began to melt until 300 degrees and
> that was only half. The rest was like concrete.
>
> It is said to split the case at the corners but the ones I tried to split
> were double walled at the corner with a PFC in one corner that got hit
> because I couldn't see it.
>
> One source said to turn the NST upside-down and lay a hot plate on the
> bottom and let it fall out. This sounds great, but the allanson I tried
this
> on, simply spewed tar out the tiny cracks of the case and never did even
> begin to loosen.
>
> Maybe I should try gasoline. I am going to try resoldering these broken
> wires by winding a copper wire around a thin needle to make a kind of
sleeve
> and slip the ends into the sleeve and solder it together. I doubt this
will
> work well tho as I can't see myself soldering this small of a connection
> with my thumbs shaking like a blurred shaver head.
>
> I haven't tried the freeze method. I guess that is next. I have my doubts
> about this too tho but heck, I've destroyed all but one of my NSTs I have
so
> whats one more.
>
> Any suggestions?
>
> Anyone interested in depotting an NST for pay?
>
> I remember Terry had a lead on a possible source of unpotted NST's from a
> factory. I replied but I guess it fell through as I haven't heard anything
> more.
>
>
>