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.
This MOSFET amplifier operating in the VHF range was found in an old American telecommunications...
This circuit for 1 kHz sinusoidal signals uses a common operational amplifier circuit and is...
This shield circuit is from old documentation. The operational amplifier used is not common today...