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[Amps] Alpha 87A Problem

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Subject: [Amps] Alpha 87A Problem
From: Michael Tope <>
Date: Sun, 26 May 2019 10:55:07 -0700
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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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