This TTL circuit is from a Radio Electronics magazine from February 1973. The circuit must be powered with 5 V and the maximum frequency depends on the TTL integrated circuit.
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...