Found in documentation from 1924, this receiver has several sets of coils. Power is supplied by several batteries and listening on high-impedance headphones.
This 2003 circuit uses two types of sensors: by reed-switch and by infrared. If the magnetic...
This one transistor stage for audio signals was found in an old publication of the year 1958. The...
Using the four amplifiers of an LM324 this circuit was found in the June 1996 issue of Electronics Now...