Found in 1968 Mullard documentation, this circuit uses period components. The transistors are matched pairs and the sensor is an Indian photocell of the time.
This circuit was found in a General Electric documentation from 1970. Equivalent transistors can be...
This circuit was obtained in a 90’s Popular Electronics. The frequency depends on C1, a component...
We found this circuit in an old American publication from 1975. It can use almost any common FET...