[Elecraft] Unusual Behavior K3S / KPA500 Drive Power Greater Than 12 watts

[Tony]

All:

I've noticed an unusual thing happen with my K3S and KPA500 amplifier 
while in SSB mode. When I increase the K3S drive beyond 12 watts, the 
KPA500 power drops-off dramatically. This only happens in SSB mode.

The KPA500 functions fine with other transceivers as well so the 
condition appears to be unique to the K3S. Any suggestions?

Tony