This circuit for frequencies of 20 to 2 kHz was obtained in English documentation from 1966. The transistor can be any general purpose and powered by batteries.
This small crystal microphone transmitter was indicated in an 80s spy book. The range depends on...
This circuit, found in a 1978 publication, converts 5 V into a symmetrical 15 V output under low...
The configuration shown in the figure is one of the most traditional when it is desired to produce...