Hi,

At the high end of the AM band, the oscillator capacitor is
at its lowest capacitance (almost fully un-meshed). So, any
variations in circuit capacitance due to tube electrode
dimensions, capacitors with non-zero tempcos or similar
happenings in the oscillator coil will have a greater effect than
at the low frequency end.

For this reason, a stable LC-tunable VFO would not normally
be designed to tune the 3:1 ratio that an AM local oscillator is
expected to.


Cheers - Joe