[Milsurplus] Relay question

WA5CAB--- via Milsurplus milsurplus at mailman.qth.net
Sat Nov 22 13:16:30 EST 2014


Jack,

I assume that one side of the coil and one side of the flakey contact are 
connected to chassis.  So you will have to know for certain which pin in the 
wall outlet goes to Neutral.  But I would disconnect the two wires and treat 
it like a flakey vibrator.  Connect one side of two 12 or 15 watt 120 V 
lamps to the wire in a suicide cord that will go to the hot side of the AC line 
when plugged in.  Connect the chassis to the Neutral wire.  Connect the 
other side of one lamp to a diode (1N4006 or better) and the other side of the 
diode to the coil.  Connect the other side of the second lamp to the flakey 
contact.  Plug in the cord and the coil lamp should glow at half brilliance 
with little or no flicker.  The other lamp should flicker at a rate which 
will depend upon the natural frequency of the relay.and the varying phase 
relation between that and the line.  Run it a few seconds, then disconnect the 
line, close the relay with (I assume) 24VDC, and check the contact 
resistance.  The contact lamp should get brighter as the contact resistance decreases 
(which may happen after only a few cycles).

DISCLAIMER:  Use an isolation transformer and note that 120/240 
Step-Up/Step-Down transformers usually are auto-transformers, with no isolation.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

In a message dated 11/22/2014 11:19:03 AM Central Standard Time, 
scr287 at att.net writes: 
> I'm wondering if anyone has ever had any success in clearing
> flaky contacts in a hermetically sealed relay.
> 
> Thought I'd ask before I start experimenting.
> 
> The relay in question is a hermetically sealed can, and
> of course it is soldered in place, in a location where
> removal and replacement would be an involved and painful
> process.
> 
> The particular contact of this relay only switches
> about 30 mA resistive, where the other sections
> of this relay are switching motor and relay coils
> and are working fine.
> 
> After 60 years of this relay's life, this particular
> contact, when closed, now shows a resistance of 20 ohms
> to open, varying when tapped.
> 
> I'm wondering if feeding the contact about a half amp
> while actuating it will clear it up, or make it worse.
> 
> To be specific, this relay is in an RT-311/ARC-38, in
> the PA tuning servo system, and this contact opens the
> cathode of the receiver audio amp to mute during the
> channel change cycle. Sometimes it is not allowing
> the receiver to unmute. I do have some "plan B"'s in
> mind, just in case.
> 
> Thanks
> 
> Jack Antonio WA7DIA/4
> 
> PS  Tried to use this radio this morning to check into the
> mil net on 3885, but signals from up north were very weak
> here in central Georgia.


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