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 found in a Philips documentation from 1970. The components are of the time,...
This circuit divides the frequency of a 2 kHz signal by 2. The circuit was found in Philips...
This circuit was found in an English publication. The components are current, and the transformer must be...