We found this circuit in the Encyclopedia of Electronic Circuits Volume 5 from 1995. It uses a 3-terminal transducer from the time. The circuit is triggered by light.
This circuit appears elsewhere in this section, but taken from other sources. This is an English...
Found in a 1975 radio amateur publication, this simple oscillator is for code practice. The PNP...
This circuit for some amps was found in a 90s Radio Electronics. The voltage can be between 6 and 25 V...