Found elsewhere in this section, but from other sources, this circuit is from a 1964 Electronic Design. The transistor is from the era and the power voltage depends on this component.
This circuit was found in an Elektor from the 90s. Next to the circuit we have a table with the...
This microphone circuit was found in a collection of American 80's layouts, using operational...
It can be obtained from Mouser Electronics, sensors (receivers) transmitters and benders for...