This amplifier with old germanium transistors is from a 1957 documentation. The power is a few hundred milliwatts and the transformers are common types of driver and output of the time.
This circuit came out in an English publication of 1976, but it can be easily assembled using...
When light fails to focus on the sensor, a common photo-transistor, the relay closes its contacts....
This traditional clock circuit with common CMOS components with discrete logic functions was found...