The HamBone

Simple receivers typically have just one LC tuned circuit, something like this primitive crystal set:
Ok, there's no antenna matching or any refinement, just leaving a single LC filter to tune the receiver. Such selectivity there is comes from making this LC as high Q as possible: nice big air-core coil and air capacitor.

Now, in the interests of miniaturizing and "modernizing" the design, I found this, by Karl Nagy:
The component V replaces the air capacitor, so lowering the Q of the tuned circuit by introducing R2 to apply capacitance-reducing volts to V. And ah! yes, there is an extra switchable capacitor in parallel with V, so as to give enough capacitance range to tune the whole AM broadcast band. -Or one could just have a single 500pF air capacitor and thus better selectivity and ease of operation? Yes, the varactor could make it small, even allow for two together to give a larger capacitance range?

Parts List for Varactor Crystal Detector Radio:

B - Battery 9 Volt - Transistor carbon zinc is fine
C1 - Antenna Capacitor - 500 pF, 200 VDC
C2 - Capacitor - 0.1 uF 50 VDC
C3 - Capacitor - 0.01 uF, Disc, 10 VDC
C4 - 1 nF, Disc, 10 VDC
C5 - 250pF, Band Extender Capacitor, Mica, 50 VDC
D1 - Diode - Germanium, point contact
L1 - Primary, Antenna coil 1 - 100 uH
L2 - Primary, Antenna coil 2 - 100 uH
R1 - Potentiometer - 10 kOhm
R2 - Resistor - 1 MOhm, 0.25 Watt, CC
SW1 - SPST Switch, Band Extender
V - Varactor Diode - Motorola MV1662, 250 pF
Magnetic headphone, or high impedance speaker

So, I tried with tuning capacitor, or varactor, and air coil or 31-mix torroid. It seems louder and to tune better with the air variety of coil and capacitor, at the cost of size, but IMHO, worth it?