Hi Bill,
I have experienced pretty much the same with my T-4XB.
After spending hours going through the Mic amp stages, replacing the 12AX7 amp etc, the only microphone I have that will modulate this rig to an acceptable average power out is an amplified D104. The rig produces full power out using the tune position, but with normal crystal mics, or even an electret that has lots of output on my other boat anchors, the Drake struggles and the Mic gain needs to be at nearly 100%
If anyone has any idea how to increase the mic amplification, I would be very interested.
Cheers,
Peter - VK2AN
Peter E