This circuit was suggested by Motorola in a 1980s publication. It is based on a PUT that is not a common component today. The division depends on the capacitor values according to the table.
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...