This circuit was found in a 73 magazine for radio amateurs of the 90s. The circuit uses two types of indicators, the diodes are for general use. The power supply is 5 V.
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...