This circuit from the 80's makes use of two transconductance operationals of the time. Modern equivalents can be used. The circuit does not need to be powered by a symmetrical source.
This circuit for the VHF band of analog TV was found in Motorola documentation from the 70s. The...
This 1989 circuit activates a protection relay if one or two phases are missing from a three-phase...
This circuit for telecommunications was found in a 1987 documentation. Connected to the...