We found this circuit in the Radio Electronics magazine of May 1977. The circuit has the frequency given by the components according to the formula next to the diagram.
This simple indicator circuit was found in a documentation from the 90s. Trimpots can have values...
Originally in the 1992 publication, this amplifier was recommended for use with record players....
This small transmitter can send its signals to a receiver placed at distances up to 100 m. The...