[Johnson] Transformer "cooking"

[David C. Hallam]

Rich Measures put out some information on how he dries out old power 
transformers by applying AC with a variac.  It's probably in the 
ham_amplifiers archives some where or maybe on his web site.

David
KW4DH

On 1/5/2014 11:28 PM, Richard Knoppow wrote:
>
> ----- 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
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