This circuit was found in an Electronics World of 1968. The transistor can be any general purpose and the double T must be set to R3 for the desired effect.
This circuit detects alternating signals that are too weak to trigger a relay. The circuit is from...
Found in a 1968 US documentation, this circuit shows how to use the resistance-scale multimeter to...
Found in a 1968 Electronic Design, this circuit makes use of an unusual ultrasonic delay line...