Thank you to everyone who replied for your thoughtful suggestions. I
hope to have some time to troubleshoot the amplifier this coming
weekend. I'll try to pass on what I discover.
73 Mike, W4EF
On 5/26/2019 10:55 AM, Michael Tope wrote:
My Alpha 87A had been working pretty faithfully up until the end of
March / early April. I haven't used it since then until this weekend.
Normally I operate remotely, but this weekend I had to come up to my
remote site for something else, so I decided to play a little bit in
the CQ WPX CW contest. I noticed right away that the tuning on the 87A
seemed squirrely on 40 meters (the amp kept re-tuning even thought I
wasn't changing frequency and VSWR appeared stable). When I moved
higher in the band to call CQ it seemed to settle down and was
delivering a steady 1300 watts.
This morning I tried operating 20 meters. At first when I was calling
people low in the band, the amp seemed okay, but when I went higher in
the band, it started acting up where it kept hunting for a new tuning
solution and in some cases it would fault. After a little fiddling, I
noticed that the frequency readout on the Alpha Remote software was
jumping all over the place (in some cases up to 16.3 MHz!!). In one
case, because of the faulty tuning, I noticed that the grid current
reading was really high, but the grid trip circuit didn't protect the
amp.
Any ideas where to start? Seems like it might be a microprocessor
problem. When it is stable, the amp is making plenty of power (1300 to
1500 watts).
Reducing drive, doesn't seem to help, so I don't think it is an RF in
the shack problem. I would put it on a dummy load, but my Cantenna is
60 miles away at my home QTH (next trip up I will bring it).
73, Mike W4EF...................
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