This circuit was found in General Electric's 1965 documentation. It appears elsewhere on the site. The SCR and the diodes must be in accordance with the motor current.
This circuit uses unijunction transistors and drives a small speaker through an output...
This circuit, found in a publication from the 1980s, can have its output voltage determined by the...
The operational amplifier for this circuit, found in a 1979 publication, may be the 741....