"I used two different transceivers--Icom 746 and 756Pro, No difference,
More significantly, I NEVER used the amp on CW, so I don't think spikes are
the issue. I also checked line voltage and set the transformer jumpers
appropriately.
What I found to be really strange was that I could operate normally, shut
off the amp, and then find that the next time I powered up, the receive was
dead and the fuse blown. My whole station is well grounded (the shack is at
ground (no pun intended) level, and grounded to two 8-foot copper rods via
short runs (straight thru the wall) of 1/2 inch copper braid) so I don't
think there could be any sort of static charge developing."
Comment:
The 746 and 756 have known issues of spikes both on phone and cw. The
symptom of the fuse blowing with the 86 off indicates something outside of
the amp is blowing the fuse. The fact that there is no problem with other
amps is because they do not have the fuse.
The fuse is doing what it is supposed to do. Get a fast rise scope and put
it on the fuse and watch. Static discharge on the antenna could be doing
it. Ground loops could also be doing it. For example, when the compressor
for the air conditioner starts, it could be creating an inductive kickback
that comes up the "excellent ground" provided at the amp.
Alpha probably gave up diagnosing it because it has nothing to do with the
amp.
Even the turn on of the amp could do it. The key is to watch the fuse and
determine when it blows. Sound like more detective work is in order.
73, Colin K7FM
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