[AMRadio] Drying out HV transformers / Chokes

Larry Will lhwill at verizon.net
Sun Sep 18 10:41:41 EDT 2005


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.


Larry W3LW

At 12:51 AM 9/18/2005, you wrote:

>Hi all,
>         Ok, I know this has been covered here before, but is there a
>consensus on how to get the moisture out of HV plate transformers and
>chokes, so they won't arc on me.  And before everyone jumps in with the
>"just put it in an oven on xxx degrees for yy hours", I am working with
>iron from a Broadcast transmitter, specifically, the Gates BC-1G so
>things are 100, 150 lbs each, and my XYL would REALLY not like it if I
>to put them in her fancy oven.  They have been sitting in an
>but dry hanger/garage for several years, so I am certain they have
>soaked up
>a good deal of moisture over that time.
>Thanks for any suggestions,
>         Don - W8HRQ
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