[Boatanchors] Relay Repair - Demagnetization Question

[WA5CAB at cs.com]

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