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Re: Unpotting techniques...
Original poster: "Albert Hassick by way of Terry Fritz <twftesla-at-uswest-dot-net>" <uncadoc-at-juno-dot-com>
Hi Mike. Excellent post! You have covered all the dirty details. Amen.
Al.
On Sat, 13 Jan 2001 14:21:29 -0700 "Tesla list" <tesla-at-pupman-dot-com>
writes:
> Original poster: "Mike Novak by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <acmnovak-at-email.msn-dot-com>
>
> Hello Everyone,
> I thought I'd take a moment and share with you some of the little
> secrets
> that I found make unpotting MUCH easier.
>
> 1.)Modified Freeze and Chip Method:
> The original "Freeze and Chip" method was NOT as easy as everyone
> claimed.
> It's dangerous for the windings and extremely messy as well. Here's
> what I
> did; First, chizel off the case using a good sharp chizel and an
> angle
> grinder to weaken the corners so they break easiily. Unclip the
> insulators
> and disconnect their wires before removal. Then place the
> transformer
> outdoors to aquire a good freeze (or in a freezer if you live in a
> southern
> climate). Next, Using a chizel (or sharpened screwdriver in my
> case:) chip
> off the thin layer of tar on the top to reveal the core. This IS as
> easy as
> it sounds because the transformer's silicon steel doesn't bond with
> the tar
> too well. Now that you've revealed the top of the core, locate the
> two pairs
> of hot wires and the GND wire. Hook the input and the GND to a
> grounded
> plug, and hook both HV leads to the core or GND connection. Once
> plugged in,
> use a plumber's propane soldering torch to heat the core. If you use
> a fine
> point flame, and stay to the center of the core, you can unplug it
> and turn
> off the torch when the tar nearest the core melts to a real thin
> liquid (and
> I emphasize THIN liquid, if you just soften it, it won't work as
> well). With
> everything unplugged, use that sharp chizel and start removing
> chunks of
> tar. It should come off real easily, and you should be able to pry
> off LARGE
> sections at a time. If it didn't cooperate, just plug it in and
> apply heat
> for another 10 mins of so, then try again. Now that you're done
> getting all
> the tar goblins off your beautiful NST, we're ready to throw her in
> solvent!!!
>
> 2.)Solvent Secrets:...
> I've had a bit of troubles with solvents in the past. For instance,
> I always
> have tar left in every crack which must be tediously removed by
> hand, and
> when I'm done, there's a big old pail of solvent which must be
> disposed of
> :( If you're using solvent to get rid of the entire block of tar,
> you'll
> have a REAL hard time getting rid of it. The best way to minimize
> the amount
> of dirty solvent is to use the smallest possible container. What I
> suggest
> is a 1-2 gallon rubbermaid container with a really tight fitting lid
> (i do
> all my unpotting indoors during the winter so the lid is a MUST).
> Completely
> disassemble the core before soaking, as It will save you time later.
> After
> you've removed the bulk of the tar from the core and coils, you
> should be
> able to put it in the sovent right away, just as long as the
> transformer is
> cool enough to touch, although a warm transformer helps the tar
> dissolve,
> you don't want it *too* hot because of the low flashpoint of pretty
> much any
> solvent. If you have access to a heated garage, then here's one
> thing you
> can do to speed up the process: Cut holes in the top of the
> container to be
> used, place a couple peices of some kind of metal (must be at least
> 1"
> thick) in the bottom of the container followed by a coarse screen.
> In the
> space created beneath the screen, place a "bubble stone" (the kind
> found in
> aquariums to add oxygent to the water) and run the tubing through
> the lid to
> an elevated position in respect to the container so the solvent
> won't
> "crawl" up the tubing. This bubbling action will act as a automatic
> stirrer
> (if you can't afford a refugee from a third world country to do it
> for you
> :).
> Now that you've got a relatively clean transformer, you *could*
> immerse it
> in oil. However, the oil will inevitably turn a lovely mud brown
> colour due
> to the tar hiding in the cracks in the laminations. Of course, in a
> acrylic
> enclosure, that gets quite unsightly. So, we're going to take the
> solvent
> process one step further. Get yourself a new gallon of solvent and
> transfer
> the contents of the used container to a milkjug using a big funnel.
> Now,
> take apart the core from the coils. Separate the shunts and the
> laminations
> into piles to be cleaned. Aquire a bit of coarse sand (or maybe even
> aquarium gravel might work). Start stacking alternating layers of a
> single
> lamination, and some sand. You'll only be able to do half of the
> laminations
> at a time if you've got the "optimal" sized container. If you've
> made the
> bubbling assembly (or the heatless boiler as i like to call it:) you
> can
> just turn it on and wait. However, if you didn't see the necesity of
> doing
> so, you will now because you'll have to sit and stirr it for an hour
> or so
> before the laminations are thoroughly cleaned. Repeat the process
> using the
> other stack of laminations and the shunts as well. Once they've all
> been
> cleaned, wipe the excess solvent off with a terrycloth rag ( paper
> towel is
> just a total pain here).
> Re-assemble the transformer the way you found it (minus about 6
> leaves per
> packet of shunts) and you've got a spotless transformer that's ready
> to be
> mounted in any kind of enclosure you desire. I suggest HV oil, but
> Vaseline
> is the next best thing.
>
> Hope that helped you brave souls who dare to venture into the dark
> black
> sticky depths of your NSTs...
> Good Luck!!!!
>
>
> Safe coiling !
> -Mike Novak
>
>
>
>
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