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.
The operational amplifier used in this application is not the most common today. The circuit is...
In the figure we have the way to trigger a 7555 CMOS monostable with a positive pulse. The time...
This circuit was found in a 1926 German publication. It is a crystal or galena (D) receiver. The...