[Johnson] Transformer "cooking"

[David C. Hallam]

Mike,

Yes, that was what I remembered.  I have a transformer that has been 
sitting in my garage for several years that I need to dry out.  I'm 
starting a linear project.

David
KW4DH

On 1/6/2014 9:28 PM, Mike Pagel, K9UW wrote:
> Is this the information you were thinking of, David?
>
> http://lists.contesting.com/_amps/2005-09/msg00203.html
>
> 73, de Mike, K9UW
> Amherst, WI
>
> -----Original Message----- From: David C. Hallam
> Sent: Monday, January 06, 2014 7:17 AM
> To: johnson at mailman.qth.net
> Subject: Re: [Johnson] Transformer "cooking"
>
> 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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>

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