[AMPS] Vacuum relays

[Rich Measures]

>
>Rich wrote:
>> >
>> >Gerard M0AIU/AA3ES wrote:
>> >
>> >> hope you are not into CW contesting. A vacuum relay has a life of
>> >>about 2 million operations. A serious CW contester will wear it out
>> in 6
>> >>days! And that is when the relay was purchased new.
>> 
>> Anybody who sends 2 million dits and dahs in 6 days is destined for
>> the 
>> nut-house.  If you need longer contact life, purchase the (tungsten 
>> contact) RJ-1H instead of the RJ-!A
>> 
>I didn't come up with the 2 million number Rich, you did. 

This is the Jennings specification for a RJ-1A operated at full ratings.  


>I posted a very simple calculation on the reflector on the 11th of February. 
In
>case you forgot, here it is again:

I did not
>........
>How long does a tungsten version last?

Hotswitched at full ratings, 1-million operations.  However, in this case 
the output RF relay does Not hotswitch, so it's a whole nuther ballgame.  
My guess for tungsten contacts, sans-hotswitching, would be something 
over 200M operations.  
>> >
>> >I have been using some RF1  vacuum relays for switching the amp
>> available a
>> >few years back here at all the hamfests at about $7-50 each, new.
>> (You can
>> >tell we're not in Nebraska!) 
>> 
>> amen
>> 
>> >They were arranged so that the bias doesn't
>> >come off the grid until the output relay has gone over: they are
>> energised
>> >for receive. I do not run QSK, but got a strange effect that received
>> >signals would all go T4, and the received signal levels would drop.
>> Tapping
>> >the relay with a pencil would restore things. 
>> 
>> This is most likely due to residual magnetism in the armature .  The 
>> usual fix is to reverse the wires to the relay coil. 
>> 
>Is this Californian black art again?

As a DC relay is operated, its armature slowly becomes magnetized- 
thereby producing a small pull between the core of the coil and the 
armature.  In time, the return-spring may be unable to fully return the 
contacts to the normally open position.  Thereby possibly causing receive 
signals to become intermittent.  .Reversing the coil polarity tends to 
negate the residual magnetism.    Another fix is to use a tape-head 
demagnetizer to remove the residual-magnetism from the relay's armature.  
.   It is my opinion that black candles are virtually worthless for 
treating this problem, Gerard.  



Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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