I used to build crystal radios when I was around 13 years old. I used visit electronics stores in the 70's and 80's and buy crystal radio parts that you could use for electronic hobby and projects building.

Once I tried using a mica condenser capacitor in my old crystal radio that I had and the sound was louder and stronger. So, I added a .006 Bakelite Fixed Condenser radio capacitor with a .001 ceramic capacitor to this crystal radio set; because it makes the radio stations wavelenth longer.
I changed the capacitors to series instead of parallel for: .001n+.006n=857.143p / or around .001 Microfarad's; instead of .007n when the were connected in appareled. If I add 2 .001 in parallel, with the .006 capacitor in parallel I will get 1.5n. If I change to a .003 and .006 in series, I get 2.0n. The capacitance recommended output is .001 to .002 Microfarad's.

I have a new 1N34A Glass Crystal Germanium Diode, and a 1940's 1N69 GE Germanium Diode for this crystal radio, but I thing either diode alone still works about the same. With two separate coils, you seem to be able to receive more AM radio stations more of the time; but the strong stations are usually always received. The electronic parts for this radio are mounted on wood blocks, so they can mount inside of the crystal radio set.

The 1N69 GE Germanium Diode was made to replace the crystal radios that used crystal detecters; and the radio stations sounded louder and were easier to use.

I found out how the electronic parts were working, at; Understanding the theory of Electronics, of a Crystal Radio Set and Radios, from what started from a simple crystal radio circuit over 40 years ago.