[Amps] Alpha 87A Problem

[Michael Tope]

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...................