Crystal Radio

The key parts to the old crystal radio were high-impedance headphones (at least 2000 ohms), a detector, a long outside wire antenna, and a good ground. Any germanium diode will serve as a detector; one type is 1N34; the original radios used a metallic crystal (commonly pyrite or galena) and a cat’s whisker (a thin springy wire with one end touching the crystal). A tuning coil or variable condenser is needed for tuning. The antenna and the ground are the two terminals of the circuit; the detector and the headphones are wired in series between the terminals, and the tuning coil is wired in parallel, across the terminals.