[Boatanchors] Relay Repair - Demagnetization Question

[Carl]

----- Original Message ----- 
From: "mac" <w7qho at aol.com>
To: "Carl" <km1h at jeremy.mv.com>
Cc: "Mark Foltarz" <Foltarz at rocketmail.com>; <boatanchors at mailman.qth.net>
Sent: Tuesday, February 02, 2010 12:50 PM
Subject: Re: [Boatanchors] Relay Repair - Demagnetization Question


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> 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?


Wouldnt actuate, just hum loudly.




>
>>
>> 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.


In an amp both sides get RF power, xcvr or amp RF; reversing polarity is the 
only thing that sometimes works

Carl


>
> Dennis D. W7QHO
> Glendale, CA
>