[Boatanchors] Relay Repair - Demagnetization Question

[mac]

On Feb 2, 2010, at 9:30 AM, Carl wrote:

> Ive had a few 24VDC relays fail to engage after several years of RF  
> use
> switching antennas on the towers. Nothing would restore them to  
> service but
> they now work fine on 24VAC.

Mark,

Do you mean they wouldn't actuate or that they wouldn't conduct  
through the  contacts?

>
> Some digging thru the P&B site and others gave info on how DC relays  
> are
> actually created.
>
> Vacuum relays as used on amps sometimes appear dead on receive.  
> Reversing
> polarity sometimes works.

Relay contacts that are not carrying any current (like the receive  
side of a TR relay)
will tend to do this.  The arcing that takes place when contacts make  
and break current tends
to have a cleansing action on the contact surfaces.  Doesn't take much  
and heavy arcing will
burn contacts,  of course.  The vacuum relay in my ART-13 does this  
and a few dozen cycles
making and breaking a half an amp or so will restore the receive side.


Dennis D. W7QHO
Glendale, CA