[Johnson] Transformer "cooking"

[Richard Knoppow]

----- Original Message ----- 
From: "Brian Burns" <brian at lessonsinlutherie.com>
To: <johnson at mailman.qth.net>
Sent: Sunday, January 05, 2014 11:55 AM
Subject: [Johnson] Transformer "cooking"


> Hello Richard et al,
>
> I heard on the air a few months ago a suggestion for 
> drying out a modulation
> transformer, and was wondering if it is just an "Olde 
> Ham's Tale". The ham
> that was suggesting it shall remain call-less.
>
> The suggestion: Short the secondary, and apply a few 
> metered volts to the
> primary with a Variac.  Raise the voltage in small steps, 
> with extended
> intervals of time for temperature stabilization. When the 
> transformer gets
> warm to the touch, let it sit for a long period of time 
> (days?) to dry it
> out thoroughly.
>
> Whaddaya think?
>
> Cheers,

     Would scare me to do.  If there is suspicion that there 
is moisture in a transformer I would remove it and bake it 
out. The ideal is an electric oven with thermostat control 
but it can be done with a makeshift using lamps to supply 
heat. The heat should not be too high,  you don't want to 
melt out any insulation. Say around 150F for a few days.
     While pure water is not conductive even a small amount 
of any salt will make it quite conductive.  I suspect most 
transformer failures that are not from plain old overloading 
or arc overs are from old insulation crumbling. It would be 
interesting to hear from someone who has done a lot of 
re-winding on what he found.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com