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



Original poster: "Garry F. by way of Terry Fritz <twftesla-at-uswest-dot-net>" <garryfre-at-pacbell-dot-net>

Replies below ...


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, January 18, 2001 6:53 AM
Subject: Re: More destroyed NST's How do I remove stubborn tar?


> Original poster: "Bill Vanyo by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<vanyo-at-echoes-dot-net>
>
> I've depotted one 15/60 Franceformer - successfully or not, I don't yet
> know.  It looks pretty clean, and I don't see any damage, but I haven't
> tried it out yet.  I'm a little unclear about what to do next - I've
> read they can be run dry, but I'm skeptical.  It seems like it would be
> pretty easy for the secondaries to arc to the core.
>

I have been told that one runs great coated in spar varnish. There should be
some sheets of plastic between the windings and the core to prevent the
arcing you are talking about. If these are not present maybe they melted.
Its been suggested to place sheets of poly between the windings and the
core. Heat the poly in hot water to make it more pliable. I haven't tried
this yet, but I am going to.

> It certainly isn't (or wasn't for me) as easy as most descriptions make
> it sound.  I used a hotplate, and as you described, got tar dribbling
> out of the bottom seams.  Then I used the hotplate on the two sides, and
> scraped out the tar when it got  soft.  It took a while, and there were
> layers of mica and junk to pull out.  Then I split the case at the seams
> with a chisel - rather easy, as it was spot welded.

Now this IS interesting. I remember reading from that book to split down the
corners but I wonder if the author didn't mean to say split down the seams.
Or maybe I kept repeatedly misreading the word seams as the word corners. I
woudn't put it past me.

>  With the help of
> heavy tin snips, I got the case off (destroying the case, unlike
> descriptions I've read where you just repot it  with vaseline in the
> original case).  I chipped away as much tar as I could with a
> screwdriver, but always being careful to drive it at a tangent to the
> surface, especially near the coils.  Some large chunks peeled away from
> the core rather easily when hot.
>

I think here is where I fail a lot. I have only one good eye and its bloody
hard for me to see angles. I am convinced that at least once, I though I was
scraping away tar along the surface but was actually digging into the
windings without knowing it.

> Then, I soaked it in mineral spirits (you said mineral oil - did you
> mean spirits?  I wouldn't think oil would work).

Yes, I meant spirits. I have mineral oil stuck in my brain and I can't get
it out.

>
> Soaking took about three gallons of mineral spirits, and two weeks, with
> repeated taking it out and removing what I could however I could -
> mostly screwdriver, some toothbrush near the end.
>

All of mine seemed to take at least 7 gallons to get it half clean.

I note that the allanson cores are very very simple. No confusion in putting
these things together.

> So now I've got it all clean, but I haven't yet figured out just how I'm
> going to reassemble it, as far as insulating the secondaries from the
> core.
>

See above. I hope it works for you.

> It would be nice to be able to buy the basic parts from the factory -
> the core, shunts, primary and secondaries> BTW, I don't have a coil yet -
I'm moving along slowly but surely toward
> that.
>

yes, it sure would be nice. I have a feeling its hard to get them because of
insureance issues. A company starts selling these and someone who isn't in
the know or careful or just plain unlucky gets electrocuted and they might
have a lawsuit on their hands.

I have heard of NST's filled with epoxy. I wonder if these hold up better
than the tar filled ones.

> -  Bill Vanyo