[Amps] Alpha 78 blowing fuses only in "Band pass" mode

Paul Jansen pjansen at cctent.com
Mon May 13 10:33:15 EDT 2013


During the recent Volta RTTY contest, my Alpha 78 popped the 15 amp line
fuses while running about 1200 watts in "band pass" mode on 40 meters.  

I replaced them and kept an eye on the meters as I slowly brought up the
drive again. I saw no indication of anything wrong on the panel meters but
it blew them again right away even before reaching 1000 watts.

So I tried 20 meters band pass - no problems.

Then I went back and tried 40 meters in manual tune mode - no problems. 

SWR on 40 is well below 1.5:1 - and I didn't notice any indication of arcing
- but maybe...

So, it would seem that I have something going on in the band pass circuit
but what?  I haven't taken it apart yet to have a look but I'm not really
sure what to look for - other than maybe loose solder connections and such.


I thought it would be a good idea to see if there may be some past history
of issues in that area of the 78.

Any thoughts would be greatly appreciated!

Thanks,

Paul / NO9C
 





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