[Boatanchors] Relay Repair - Demagnetization Question

[Carl]

Automotive and other vibrators do not have coil problems. The contacts are 
"welded" together from basic chemical reaction after decades of storage. 
Applying 6-12VAC across the proper actuator contacts will get it swinging 
again.

Carl
KM1H


----- Original Message ----- 
From: <WA5CAB at cs.com>
To: <boatanchors at mailman.qth.net>
Sent: Tuesday, February 02, 2010 2:23 PM
Subject: Re: [Boatanchors] Relay Repair - Demagnetization Question


> Although not technically hermetically sealed, plug-in vibrators (except
> VB-16) are sealed well enough to have this problem.  According to my
> experience, the MTBF of NOS units was 40-50 years.  I first noticed it 
> occurring with
> WW-II vintage units in the late 80's.  By the mid 90's it was showing up 
> in
> Korean War vintage units.  Today I assume any unused vibrator will not 
> work
> initially out of the box.
>
> It has nothing to do, of course, with magnetics.
>
> In a message dated 2/2/2010 12:10:13 PM Central Standard Time,
> jhhaynes at earthlink.net writes:
>> When the use of hermetically-sealed relays first started, especially
>> in the military, there was a surprising development of contact failures.
>> After all, you'd think that a sealed relay couldn't get dirty contacts.
>> It turned out that organic substances outgassing from the winding
>> would, with the help of a little sparking, form an insulating goo on
>> the relay contacts.  So for a while there was a doctrine that you
>> don't use a sealed relay unless the situation absolutely requires it;
>> that a simple dust cover is much better for contact reliability.
>>
>> There is an awful lot of lore about contacts and their problems and
>> solutions.
>>
>
> Robert Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480
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