This is where a grid diper is handy, since you are measuring the resonant
frequency of the circuit, without anything else. Check the resonant
frequency of the coils in both S-20R radios. At the calibrated frequency,
they should be the same.

There could be a number of problems - especially if someone has fiddled with
it. Are the coils the same? At 12 MHz, the frequency is off. I think you
will find one of these possibilities:

1. There is a unwanted fixed capacitor in the circuit.
2. the adjustable capacitor does not go down tominimum capacitance.
3. The coil is not adjustable like it was intended.
4. Someone has added turns to the coil.
5. Someone has removed the correct slug and substituted another core of
different material.

I would suspect 5 first if everything else looks normal.

Once in awhile, you will find something like that that probably slipped
through from the factory - but not likely.

73, Colin K7FM