Re: weird nst

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

Original poster: "Scott Hanson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <huil888-at-surfside-dot-net>

Antonio -

These "pressed together" core assemblies need some special tooling to get
them apart without bending or spreading the laminations. A hydraulic press,
or a large arbor press is best, but a large machinist's vise can also be
used with a bit more difficulty. Basically, you need to support the outer
core at two places as close to the "joints" as possible. Machinist's
parallels work great. Then, you need to fabricate a U-shaped "pusher piece"
(or stack up suitable pieces of heavy steel stock )that will press down on
the inner core structure, again as close to the joints as possible. Try to
see which direction the core was originally assembled from, and press it
apart in the opposite direction (press it back out). Usually there will be
some minor distortion of the outer laminations so you can see the original
assembly direction. All of the transformers I have seen that utilized this
"pressed together" construction also had integral shunts, so if you are
looking to increase output current its a bit more difficult than with
removable shunts. Grind about 1/2 of the shunt face area 3/16" to 1/4"
shorter, and you should see a 30-40% increase in current.

This construction seems to be common in the smallest, cheapest NSTs, like
the non-potted "indoor" variety.

Regards,
Scott Hanson
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, November 19, 2002 4:10 PM
Subject: Re: weird nst


 > Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>
 >
 > Tesla list wrote:
 >  >
 >  > Original poster: "Andy Cobaugh by way of Terry Fritz
 > <twftesla-at-qwest-dot-net>" <kb3ewy-at-rcn-dot-com>
 >  >
 >  > That looks like the Jefferson 12/30 that I depotted.  The core has to
slide
 >  > out.  Well, slide is an understatement.  It took probably two hours
with a
 >  > hammer and screwdriver to drive the core apart.  Even then, I had to
grind
 >  > the core to make it fit back together because all the pounding spread
and
 >  > deformed the laminations.
 >
 > Hummm. A NST that I mentioned some weeks ago, that was not working well,
 > has also a Jefferson label and is constructed in that way, although
 > with just two windings. There is really a partial short somewhere.
 > The input current with the secondary open is too high (~0.9 A), and
 > changes just a little (~1 A) if I shorten the secondary. The secondary
 > gets hotter, so I think that the problem is there. I would have to
 > rewind the secondary, but for this I have to open that core.
 > A practical suggestion of how, with only minor destruction, would be
 > welcome.
 >
 > Antonio Carlos M. de Queiroz
 >
 >