Bill,
I use my Flex 5000A with an ALS-600 and the only time it ever faults is
when I forget to manually set the amp's bandswitch to the correct
frequency range. The first question I would ask is if you transmit into
a 50 ohm dummy load does the amp behave correctly? Since you are using
the Palstar antenna tuner I would assume there is no mismatch, but there
is a possibility that you have RF feedback and an oscillation is causing
the Flex to take off, which the amp will interpret as too much power
appearing on its input. I'd be most suspicious of that scenario.
A second thought is that the ALS-600 doesn't need a whole lot of drive
to make 600 watts PEP so I wonder if maybe you have a peak here and
there that crosses the threshold that the fault circuit will tolerate.
The ALC adjustments on the back panel and front panel of the ALS-600
will have no effect since there is no ALC connection between the Flex
and the amplifier.
Are you using the leveler in PowerSDR? Although it doesn't seem to work
as effectively as a hardware limiter, it might help to control a rogue
peak that sneaks through here and there. After a couple of years of
using the native voice processing within PowerSDR I ended up running my
station's external audio chain into the balanced input on the back
panel. The last active element in the external audio chain is the
compressor/limiter which I use to brick wall the audio peaks so that I
can raise the average audio content much higher than is possible with
the voice processing within PowerSDR. That approach has made a huge
difference in the loudness of my signal with voice modes and has
eliminated the excessive peaks here and there that used to show up and
cause mischief. The ALS-600 seems very comfortable with this approach,
and my AL-82 never flinches no matter what I pour into it with the Flex.
Good luck!
Rob W1AEX
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