Warning about Magnetek(sp?) Jefferson NST's and a depotting question.

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

Original poster: "Garry Freemyer by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Garry-at-NDFC-dot-com>


About a month ago, I acquired a used but relatively new brown 12/60 NST from
Magnatek Jefferson or something like this and it fried immediately when put
into service despite having a safety gap and two chokes like the ones
reccommended by the coiler that wrote a book on making coils. I forgot his
name but I've heard the book highly reccomended.

During the course of depotting I noted a few significant things. ....

The tar was severely cracked and dried out compared to the other trannys
that were in the same sign and were of the same age.

The tar did not extend around the entire transformer. The sides were clear
of tar which led to the third observation ...

One of the secondaries of the tranny was arching to the case that was MUCH
LESS THAN AN EIGHTH OF AN INCH AWAY!!

Obviously, the transformer should have been much farther from the case or a
sheet of insulation should have been placed between the secondarys and the
case. 

When the unit fried, I could HEAR the arching inside and smoke arising out
of the transformer after the lid was removed. Had tar been present, the unit
might not have shorted so easily. 

The arching of course melted the windings at the point of arching.

I am posting this to warn coilers that if you get one of these units, don't
try to run it in the pot, depot it at once because you might ruin the unit
by trying it out in a tesla app. 

I also have my suspicions that the reason the sign failed and had to be
dismantled was because this particular tranformer was shorting to the case.

---

Also, what is the correct temp for melting tar out of a tranny in an oven
without having the tar smoke a lot? I seem to remember 200 degrees, but the
tar wasn't even soft with this temperature after 45 minutes.