This circuit is from American documentation from the 70s. This configuration appears in this section obtained from other sources. The signal is sinusoidal determined in amplitude by D1 and D2.
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...