This circuit, obtained from a 1965 magazine, can still be assembled using some modern equivalent components. The transistors may be BC558 and the transformer is obtained from a disused transistor radio.
This sensitive circuit with common transistors was found in the Radio Electronics magazine of July...
April 2017 - Mouser Electronics owns standard Qi wireless charging coils for a power range of up...
This circuit works only with carbon microphones, due its low impedance. The speaker should be good or...