The transistors of this circuit found in an English 1980s documentation may be the modern BC548 equivalents. The circuit is battery powered and the earphone must be crystal.
This interesting circuit of a 1988 documentation consists of a mouse trap where the sensor is left to...
This circuit is from a 1968 General Electric manual. It produces a pulse of light when fired,...
This good amplifier with output in complementary symmetry is from an old publication, and modern...