|[AMRadio] Drying out HV transformers / Chokes|
lhwill at verizon.net
Sun Sep 18 19:49:23 EDT 2005
I found a source for transformer varnish on the internet. That
varnish is very volatile and you may have trouble getting it as an
individual. (the flash point is around 70 degrees with a spark as I
remember and it has a short shelf life according to the mfgr.). I had
no trouble but I am a licensed Professional Engineer. An option for
the units is to find a motor rebuild shop. They usually have a 55
gallon drum of it that they dip the rewound motors into when they are
done. I sure they would do it for you for a modest fee. I have no
source on the tar or fish paper etc.
At 01:00 PM 9/18/2005, you wrote:
>Hello Larry and All,
>I have several 2.5v and 10v rusty,dirty, and rattling UTC small can
>S series filament transformers that I want rebuild and would like to
>know a source for transformer varnish and potting material, wax,tar,
>On pulling the cover off the most rattling around one I found only
>sections of corrugated cardboard to be the
>"packing/potting" material !!. I would like to use something better
>and improve the heat transfer as these seem to be really small
>construction for the rated current. I intend to use the 10v units
>for 813/814/805 family.
>Any suggestions would be appreciated.
>From: Larry Will <lhwill at verizon.net>
>To: w8hrq at lemleys.org; Discussion of AM Radio <amradio at mailman.qth.net>
>Sent: Sun, 18 Sep 2005 10:41:41 -0400
>Subject: Re: [AMRadio] Drying out HV transformers / Chokes
>Here is the section in my article from ER Magazine on rebuilding an
>RCA BTA-1R1 on the homemade over I used with great sucess. all you
>need is a thermostatically controlled hotplate a thermometer and a hood.
>.from my RCA BTA-1R! article in ER.
>A check of all the iron with a 1000V 1000 megohm ohmmeter showed
>excessive leakage (less than 1000 megs) in the modulation reactor,
>the driver plate transformer, and the control transformer. The
>control transformer makes 110VAC for relays and lamps from the 240V
>input. The smaller transformers were baked in the kitchen oven at
>140 degrees F for 5 hours. For the very heavy 50 henry modulation
>reactor, I fashioned a homemade "oven" using a thermostatically
>controlled single burner hotplate and a hood made from an old water
>heater jacket (Figure 1). This allowed me to cook the transformer
>out in the garage near the rig. An oven thermometer allowed me to
>set the oven temperature to 140 degrees F and after 25 hours of
>"baking", the leakage was cured. All of these transformers and
>chokes were then dipped in transformer varnish to re-seal the
>winding from new moisture incursion.
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