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[Amps] Help please: Converted Alpha 78 blowing fuses

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Subject: [Amps] Help please: Converted Alpha 78 blowing fuses
From: "Mike & Becca Krzystyniak" <>
Date: Wed, 13 Jan 2016 11:05:43 -0600
List-post: <">>
Greetings all,

    I'm looking for this groups sage advice.

    A friend dropped off his Alpha-78 that was converted to a pair of
3CX800's along with adding the PWD transformer P/N "Alpha 76A-2.  In CW mode
the amp powers up and works.  When I hit the SSB button, I hear the HV relay
try to switch and there are sounds of arcing and then of course the fuse
pops.  This is all within a few hundred milliseconds of pressing the SSB

    I can't find the smoking gun here.  No real evidence of what is failing
or flashing over.  I took apart the filter cap stack, looing for arcing pits
or carbon scoring.  I did not see any evidence of things punching down
through the rubber insulator to the chassis.  Then I carefully unwound the
HV cable harness looking for a pinch that might have punched through and
found nothing.  Then I also disconnected the B+ wire that goes over to the
RF deck and no change.  

    For grins I measured the voltage across wach cap in CW mode and 5 of the
6 had equal drops of about 290V, but one of them was lower ~245V.  Not sure
what it means but is a data point.

    Has anyone seen something like this before.  Comments and suggestions on
what to look at next would be most appreciated.

Thanks in advance.

73's MIke K9MK/5


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