Found in an old Popular Electronics this circuit is still current. The SCR can be of the 106 series and the relay according to the voltage used in the supply. The voltage can be 12 V.
Found in an Elektor from the 90s, this circuit is suitable for viewing audio signals on an...
This project was found in a 1982 publication, using only two transistors. Signal injectors are...
Found in documentation from the 1980s, this circuit uses components from that time. The circuit is...