[Amps] vacuum relay failure

[Pete Smith]

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, or might there be 
something else in play?  Is it logical to consider a possible causal 
relationship between the output and input relay failures, or just 
coincidence?  I should mention that the Hi-G is only rated at 75 watts CCS, 
so it probably doesn't have too much headroom for a typical 100-watt 
driving signal.

73, Pete N4ZR
The World HF Contest Station Database
was updated 20 Oct 2004
2796 contest stations at
www.pvrc.org/WCSD/WCSDsearch.htm