This crystal or galena radio was found in documentation from the 1990s. The earpiece must be a high impedance crystal or magnetic earpiece and D1 can be any germanium diode.
This circuit was obtained in an old Argentine publication, using germanium transistors and...
This very low resistance meter was found in the February 1995 issue of Electronics Now magazine. The...
Using a CA3130 operational amplifier, this circuit was found in an English publication from 1977....