We found this circuit in a 1963 Radio Electronics. It can be used for remote control. The frequency depends on the coil and the power is supplied by a single battery.
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...