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

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

Original poster: "Mike Novak by way of Terry Fritz <twftesla-at-uswest-dot-net>" <acmnovak-at-email.msn-dot-com>

Garry,
snipz below...

> 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.

This problem can be solved by another batch or solvent and some PATIENCE!!!
Brute force and fragile depotted NSTs do not mix! I've run into the same
problem, but I just changed the solvent. Also, read my post about unpotting,
it says to use an aquarium bubbler. That's what has worked best for me.
Although, it's best to do that part outdoors.

>
> 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.

He he he... that's what I first thought. It takes time, solvent, time, and
more time. I've had one TERRIBLE unpotting experience which led to all my
revisions of the process. If you put in a little thought you can find easy
ways to do the most dreadful tasks.

>
> 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.

Obviously the author never actually attempted to unpot anything.... My first
attempt took 5 gallons of gas to dissolve HALF the tar!

>
> My own experience is FAR from anything like this. I spent SIX WEEKS
soaking
> a transformer in mineral oil.

Hate to break it  to ya, but mineral oil is a POOR solvent!!! Mineral
spirits is what you'll want...

>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?

All I have to show for my unpotting days is some NICE  clean cores. I'm
making a saturable inductor for current limiting using a 12/60 core and 80
turns of #10 wire.... If I had a decent bobbin, you WOULDN'T be able to tell
the difference between mine and Richie's! (other than the number of turns :)

>
> 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.

That is such a stupid thing to tell people! I don't think ANYONE should try
this method. I did, and it was messy and fruitless.

>
> 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.

Hey, that's your fault. They said split the case not the entire corner. Take
your time and stay to the edge next time.

>
> 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.

I tried this with a waffle iron and I managed to remove about 1-2 pints of
tar after 4 hours, but it obviously wasn't worth the time spent in the cold
garage.

>
> 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?
>

Read the last post about unpotting and you won't have such a hard time.


Best of luck,


-Mike Novak

> 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.
>
>
>
>