I had an unusual condition today that seems to be the prelude of my Alpha
77Dx's 8877 going bad.
Shortly after applying AC power (about 20 sec.), the HV was reduced from
what is normally 2600VDC during filament warm-up down to 2300 VDC and plate
current ran about 40 mA where it is normally biased off until the 3-minute
timer function completes. After the 3-minute timer completed, the amp's key
line was working fine, but both LV and HV read much lower than normal and
plate current was still idling around 30-40 mA where it is otherwise
normally biased off until PTT is applied. Observing the amp's meters, there
was no indication of RF drive from the transceiver whatsoever. In other
words, there was no change between standby and either LV or HV. except that
plate current idled at 40 mA and HV was lower in both positions.
I re-started the amp a few times. On each successive attempt the fault
condition as described above lengthened, beginning at 20 seconds, then about
60 seconds on the 2nd power-up, then 2 minutes on the third power up
attempt, and finally everything was normal on the fourth and power-up
attempt. Full RF power now and everything is running 100%. No snaps,
crackles, or pops at any time.
Thoughts?
Paul, W9AC
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