[Amps] vacuum relay failure

[R.Measures]

On Nov 22, 2004, at 8:17 AM, Pete Smith wrote:

> I do not use this amplifier QSK,

Pete --  With modern transceivers, there is usually no timing 
difference between QSK-CW and SSB-VOX.

> 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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>
>
>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org