[R-390] Power Transformers

[Drew Papanek]

Bob Camp wrote:

<snipped>

>So, has anybody ever seen a blown power transformer in one of these radios? 
>If so do you have any idea what caused it to fail?

The only "failure"  that I have personally witnessed is emanation of a loud  
acoustic hum.  The transformer in my '67 EAC exhibits that behavior, but 
electrically all is copacetic.  I had heard of a remedy  consisting of 
baking the transformer at sufficiently high temperature to reflow the 
internal tar.  After removal of the rectifier bracket and associated wiring 
I tried baking for about an hour at 250 degrees F IIRC.  Small amounts of 
tar leaked out of a corner proving that the tar had liquefied.

After cooling, I powered the transformer  (no  load) and it still hummed 
loudly.  I tried baking several times again with transformer in various 
positions and it still hummed upon subsequent test.

My final "solution" was to loosen the 6 captive mounting screws a turn or  
two and stuff an old glove
between the transformer and the table upon which the receiver sits.  That 
acoustic isolation damped
the sound down to an acceptable level and has worked well for at least 15 
years now.

I have read  anectdotal reports of dielectric failure of the rubber 
feedthroughs for the high voltage
terminals.  Those were repaired IIRC by replacement with insulating tubing.

Drew

_________________________________________________________________
Don’t just search. Find. Check out the new MSN Search! 
http://search.msn.click-url.com/go/onm00200636ave/direct/01/