I remember measuring the capacitor at 0 - 130 picofarads, but it may have been a little different, standard size. I'm not sure what the standard is for AM, maybe 1/2 of the old style 365 pfd, which would be 182.5 pfd. I measured 130 max, but my meter has long been out of calibration.
The ferrite loopstick for the coil, it is 4 1/2 inches long, 1/4 inch wide on the flat side of it. Its not round, more of an oval; standard ferrite coil.
Primary coil wound with about 60 - 100 turns of wire, loosely wound, with double the width of the wire spaced between the turns, if that makes sense. Used solid 22 guage wire. Secondary coil is 7 turns same guage wire, wound in the center of, and over top of the primary. It's even more loosely wrapped 1/4 inch space between the turns on the loopstick.
If I can get my friend to snap some more digital pics, I'll try to post a decent pic of a close-up on the loopstick.
The 60 - 100 turns on the primary was me being lazy. I started w/ about 100 turns, and kept taking coils off until I could tune the full AM band.
Otherwise, resonant frequency = 1 divided by the quantity of 2 pie times square root of product of inductance of coil and capacitance.
Formula calculating inductance of coil is much worse; too many variables to account for.
The easiest way is to get a matched coil and tuner from an old radio, or a crystal kit. I had built another prototype a few months ago, and that is what I did. A good tweak if you use a standard loopstick is to make your own secondary, and feed one end of the lead back thru the center, pressed against the loopstick. Details about this technique are here:
http://www.geocities.com/hamfiles/