In trying to get an old Delta 580 running I've run into an instability
on the 10 meter band. The PA takes off into a sing once I hit it with
some drive. Reducing the drive to zero does not cause the output to go
away. Oscillation is in the 10 meter band, but the PA is maxed out at
about 90 watts. ALC light is on. The only way to stop it is to return
it to receive. The PA is stable with a purely resistive load on 10
meters. Connect an antenna with a little reactance, bring the drive up
and it bangs to the rails. I've checked internal connections etc.
Removing the output cable from the low level amp to the PA will stop the
oscillation. Looking at the output of the low level amp, it seems
stable with the PA unplugged.
All other bands look clean and stable. Any clues or suggestions will be
appreciated.
Thanks in advance.
73
Bob K4TAX
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