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 three-transistor circuit was found in Radio Electronics magazine from May 1969. The circuit is...
This is the old name given to flip-flops or biestable multivibrators. In fact, this is a 1967...
Found in a publication from the 60's, this circuit makes use of germanium transistors of the time....