Found in a 1966 Electronics World, this circuit applies to the protection of any analog instrument. The diodes can be of any general-purpose type.
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....