Given two identical coils magnetically coupled on the same core:

Wiring them in series gives single winding with twice the number of turns.

Inductance is proportional to the number of turns squared, so doubling the turns should give 4 times the inductance of a single winding.

4 * 160uH ~= 600uH so that makes sense.

Do you think the capacitor is located between the coils in the antenna resonator for a reason, or can it be placed anywhere as long as it is in series?

It seems to me that this series capacitance is perhaps one way to improve linearity?

As for the tank, since the windings are magnetically coupled, I would think whatever one winding "sees" the other will "see" as well, so they could be lumped together for a first order analysis (but my coil intuition is still taking baby steps).

What I don't get is how the oscillator works. If drive and sense are on either side of the capacitor, at resonance you get a 90 degree phase difference, but the tube gives 180, correct? [EDIT] Oh, I think I see it now. The coil ends are shorted at AC, so it looks like a parallel tank, with 0 degree drive/feedback.