[Johnson] Transformer "cooking"

[Carl]

I would not suggest running at maximum current as moisture saturated 
fishpaper insulation is already compromised. Get the iron just hot enough 
and a bit over to do the job.

Carl
KM1H



----- Original Message ----- 
From: "David C. Hallam" <dhallam at knology.net>
To: "Mike Pagel, K9UW" <k9uw at wi-net.com>; <johnson at mailman.qth.net>
Sent: Tuesday, January 07, 2014 8:07 AM
Subject: Re: [Johnson] Transformer "cooking"


> 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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>>
>
> -- 
> "I predict future happiness for Americans if they can prevent the 
> government from wasting the labors of the people under the pretense of 
> taking care of them."
> Thomas Jefferson
>
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