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

[Carl]

I would consider the electrolytics may becomin leaky and in the bandpass 
mode the PS is drawing enough extra current. BTW, you wont see leakage 
current on the meter.

Carl
KM1H


----- Original Message ----- 
From: "Paul Jansen" <pjansen at cctent.com>
To: <amps at contesting.com>
Sent: Monday, May 13, 2013 10:33 AM
Subject: [Amps] Alpha 78 blowing fuses only in "Band pass" mode


>
> 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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