The figure shows a remote-control receiver working the 27 MHz band, very popular in the 60’s. The circuit us from a February 1961 Radio Electronics magazine.
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...