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.
I found this circuit in a 1986 English magazine. It can still be easily assembled, replacing the...
We found this circuit in a technical documentation on the National Semiconductor LM3909. The...
This circuit is suitable for applications in medical, research and industrial equipment. The...