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Re: [TCML] Subject: Overheated Secondary
Inner windings are connected to the core (which is center tap
configuration). Each secondary puts out about 6kVrms in your tranny. The
outer portion of the secondary winding is the high voltage end. This is
the area which usually shorts and your tranny appears to be no
exception. Typically a 2 or 3 layer removal will solve the problem. Some
damage occurs just in the depotting process itself from mechanical
stress of removing the tar. But, after a few layers of unwinding the
damaged area of the effected secondary, it's good as new again.
I like to use new GTO cable on the hv outer secondary windings (which
the tranny originally used). It's good for 15kV insulation and perfect
for NST rebuilds. I bought like 100 feet of this stuff a year ago and
it's come in real handy (not all that expensive either). You may have
found some gasket or cardboard material in the potting compound. Insert
something similar when you repot the tranny. Allow the cardboard to keep
the GTO cable out of harms way (mechanically and electrically meaning
more space away from core and case is good).
Removing 1/2 the shunts will put your transformer into major power mode.
The tranny will push a lot of current to the cap bank. It's not linear
(if you remove about 1/2 the shunts your current may go up x3). However,
that's what I did on my 12/60 and achieved about 200mA (big jump in
current). My shunts where divided into two sets. Yours looks a bit
different, but regardless, remove 1/3 to 1/2 of the shunts to boost the
current. The difference is night and day.
Something I did was to remove several secondary layers to reduce the
output voltage. When I removed 1/2 the shunts, I got a big current boost
and reduced the voltage to a manageable level. Don't remove more than
say 15 layers however. That will reduce your voltage down to about
10.5kVrms and it's nice to keep the output voltage near the original
value as much as possible. However, if you find yourself unwinding more
than you actually wanted to, don't worry about it too much. Simply
adjust the gap for the new lower arc voltage. It will do fine and due to
the current increase, much better than previously realized.
Try the tranny dry during shunt reduction. If you like it, pot it with
your flavor of potting compound (wax, oil, whatever). Use trial and
error with the shunts. If it seems like a bit much, add a few more shunt
slabs in there until you find what your coils happy with. But
definitely, while you have it apart, now is the time to beef it up by
removing 1/3 to 1/2 of the shunts. That's exactly what I would do.
My photos are here: http://members.cox.net/kc5gym/
I have a question or two, maybe a million.
There is a picture of the shunt in my hand. I should remove 1/2 of these?
I was not able to preserve the original "angel hair" wire terminations
on the secondaries. Are the inner windings
connected to center tap or are they the hv ends? I suspect the outer
ends are the outputs.
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