[Elecraft] K3 Amplifier Drive Inconsistency

[Bill Schwantes]

I need help solving an amplifier drive inconsistency problem when I operate
using digital modes on 50 MHz.  I noticed during a recent contest that the
K3 will sometimes key the amplifier but provide zero drive. I'm using K3 SN
669 on 50 MHz FT8, FT4 and MSK 144 and driving a KPA1500 to about 750 watts.

After several consecutive transmissions I notice that the amplifier
responds briefly to being keyed but the power drops to zero. It's keyed up
but has no output.  The K3's output (drive) is set at 17 watts but there is
no output on the RF meter when this happens. The K3's red TX indicator is
on. This problem also occurs when driving a KPA500, though less often

I can correct this problem temporarily by switching the amplifier to
standby, which allows the K3 to  change to "barefoot" output then switch
the amplifier back to "operate" which changes drive power back to it's
preset level.  That's usually good for a dozen or so transmit cycles before
the problem reappears.

This problem does not occur when driving other amplifiers; nor does it
occur when using CW or SSB modes. It seems to have something to do with the
K3/KPA1500 command interface controlling the output power of the K3.

Any ideas?

73 Bill W7QQ