Published in Popular Electronics with the curious name of Obnoxious Noisemaker, this 1968 circuit generates random sounds that are reproduced on a loudspeaker. The power transistor can be a BD136.
This General Electric circuit is from the 80's. The PUTs used in this meter are not common...
Found in a 1964 Electronic Design, this circuit generates pulses based on an avalanche diode of...
This circuit, which consists of an audio oscillator, was found in a Radio Electronics magazine from...