This circuit is from an American manual from 1975. The transistors are types of the time, but equivalents can be used, as well as the relay that can be according to the supply voltage.
The time the output is high (1) of a TLCSSB in the astable configuration depends on Ra and C. The...
Found in a publication from the 60's, this power supply has no regulation, but only current...
This short-range circuit can act as a wireless microphone. We got the schematic and the printed...