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Re: Unpotting techniques...



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

Thanks Al, but there's still more to be said...
For instance, Ii found out what happens if you do not heat the core and
coils before chipping: the secondary remains as brittle as the tar and will
chip off along with it!!! Just a moment ago I was hacking an Allanson I was
hoping to parallel with my 12/60 Franceformer, but I lost a part of the
secondary without even touching it!!! Also, I noticed that although
Allansons are not a bad type of NST, they have small cores (about the size
of a 15/30 core on a Franceformer in my 12/60).
Now, I've got only one 12/60 which is not unpotted yet, So it looks as
though I'll have to go NST hunting tomorrow.  I want 15kV units REAL bad.
I've been using 12/60s almost exclusively  : |
So, in conclusion, make sure you heat the core and coils BEFORE BEGINING to
chip the tar off!!!! Lesson learned : (

Best Wishes,

-Mike Novak


PS- If anyone would be interested in an unpotted 12/60, drop me a line at
mailto:acmnovak-at-msn-dot-com
I'll consider trades, but I'm really broke so $ is preffered. :-\



> 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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