Hi Dave,
I have a THP HL-1.5KFX that I have mated to my K3/P3
pair and it works flawlessly. I purchased the amplifier from
Array Solutions and they supplied a control cable that uses
the ACC connector on the K3.
The P3 uses the RS232 connector.
73! Ken Kopp - K0PP
ElecraftCovers at rfwave.net