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 indicator circuit used and game machines (arcades) to indicate that the machine is being...
This circuit fires at the touch of a sensor, passing its output from high to low in a time given by...
This circuit is from an English magazine from 1978. The circuit can be assembled with BC557, BC547...