This circuit was found in a documentation for radio amateurs from the year 70. Its purpose is to produce a tone on a transducer when transmitting messages in SSB telegraphy.
Using an operational that is not common today, but which admits a modern equivalent, we found this...
This simple source of up to 1 A can supply voltages according to the secondary of the transformer, in this...
This interference rejection circuit for telegraphy was found in a 1980s documentation for radio...