[Elecraft] amp tune

[jeff kb2m]

I'm trying to setup my K3 to tune my tube amp. I have TUN PWR set to 25
watts. when I long press the tune button the K3 goes into transmit at the
selected 25 watts, in CW mode, but the amp doesn't key. If I press the PTT
on the mic the amp goes into tx. I must have a menu set wrong? The only
connection to the amp (other then the coax!) is the RCA connector key out on
the K3. on  Tuner is in bypass, ext ALC is OFF. Any ideas??

73 Jeff kb2m