I made a couple of crystal sets as a child. In 2015 I was given some variable capacitors and germanium diodes so I made another one. There are few AM stations in Germany (where I live) so I was very pleased to tune into the English Language Service of Radio România Internațional on 5939 kHz from Statia Radio Galberni, 1165 km away. I wrote and told them and, to my delight, received a QSL card.
Details (nothing special) - antenna 12m. long, 1.80m. above ground, earthed to a radiator, antenna capacitor 330 pF, tuning capacitor 660pF, coil 70 turns of 0.3mm wire with taps every 10 turns, 1N34A germanium diode, piezo earphone..
Also experiments with various home-made parts: a coil with two sliders, a piezo earphone, a high-impedance earphone and a cat's whisker with a lead galena crystal.
2021: In the meantime I've added an LM386 audio amplifier module to pick up distant transmissions. Cheating of course, but Germany has now entirely abandoned AM transmissions. With the LM386's help, reception is loud (by crystal set standards), even with the cat's whisker, but at present selectivity is poor. Basically, I am limited by my 12 meter antenna which has to be set up surreptitiously at night in my Berlin courtyard.