[Amps] vacuum relay failure

[Pete Smith]

I do not use this amplifier QSK, and have it set up with a speed-up circuit 
in any case.  Normally, I run 20-30 Ms of PTT delay to protect the relays, 
but that's not really practical with hand keying.  I may have been doing 
some hot switching.  The output relay is an HC-1

Thanks for the confirmation.

73, Pete N4ZR

At 10:34 AM 11/22/2004, R.Measures wrote:


>On Nov 22, 2004, at 7:02 AM, Pete Smith wrote:
>
>>I modified my SB-220 about 5 years ago with vacuum relays on the input 
>>and output.  It has had a lot of hard contest use since then without 
>>incident, but this weekend, after about a half hour, I noticed that I was 
>>intermittently getting no output from the amp, even though the 
>>transceiver looked like it was putting in normal drive.  It seemed to 
>>change from one switching cycle to the next -- sometimes it would go a 
>>dozen QSOs with no problem, but on the 13th nothing was getting out.
>>
>>About an hour after this started, the input relay (a Hi-G d'Italia 
>>surplus job) started not closing intermittently, leaving me with no drive 
>>either, so I shut the thing down altogether.
>>
>>I have replacement relays on the way, but would like to tap the 
>>experience on the list -- does this sound like just contact failure,
>
>Yes, Pete.  A vacuum relay equipped amplifier that is used with a modern 
>transceiver is at risk of hot-switching if it does not make faster than 
>the transceiver.   Cu-contacts are especially vulnerable to erosion from 
>hot-switching.  Since modern transceivers typically begin to produce RF in 
>5 -  8mS, only a few vacuum relays are capable of switching fast enough -- 
>and even then, a speed-up circuit is needed to initially overwhelm the L 
>in the relay's coil.  Satisfactory relays for this job are the Jennings 
>RJ-1A and the Kilovac HC-1.  In order to get enough speed-up, 3 - 5x the 
>coil V needs to be available during make.
>http://www.somis.org/D-a-07B.jpg
>
>>...
>
>Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>
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