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 is one of many configurations with a 4-input mixer transistor that can be found on this...
This dimmer was found in the Electronics Experimenter Special projects of 1983. The circuit uses...
The operational amplifier used is the 741, but the configuration is valid for other operational...