Been doing some more work on the SixBox AM transceiver and have come up with a simpler and better TX lineup. I abandoned the osc/multiplier in one stage and went instead for a 3rd overtone xtal followed by a modulated buffer and PA. The third overtone oscillator values shown ensure the crystal reliably oscillates on its 3rd overtone.
The little PA and buffer work well with just T37-6's as (untuned) chokes in the collectors of the buffer and PA followed by a low pass filter. This arrangement is very stable and simpler than before. Modulation is clean and deep. As it stands it produces 50mW of AM on 6m. A further single stage linear PA would take this to around 1W of AM, but I will leave this to others.