This circuit is used to detect PLL signals from the 4046 IC. The circuit is from an Electronics Now from October 1994. The indication is made through LEDs.
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...