[Amps] Alpha 87A Problem

[Michael Tope]

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