For signals up to about 500 kHz modulated in amplitude and transmitted by the power network, the figure shows the receiver. The circuit is from a Radio Electronics from February 1989.
This circuit is from a 1974 publication, but it can still be easily assembled today with BC548...
Found on Popular Electronics in the 1980s, this circuit detects a change in air pressure using a...
This 3-transistor amplifier stage was found in documentation from 1963. The transistors are made...