In this 2001 circuit we have the way to trigger an SCR with a phototransistor. The circuit appears elsewhere in this section, obtained from publications from different eras.
This circuit triggers an alarm when the mains power is cut off. The circuit was found in the July...
This acutely tuned circuit was found in American documentation from the 1960s. The transistors are germanium...
This small AM transmitter was found in American documentation from the 1980s. Transistor support...