This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
This circuit was found in a documentation from the 90's. Power is included, and the regulating...
We find this circuit in the 80s used integrated circuit manual itself. The integrated circuit is not...
This sweep generator or current-controlled oscillator was found in Popular Electronics from...