This circuit was found in documentation from the 80s. It is based on unijunction transistors not very common today being synchronized by the 60 Hz power grid.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...