Found in 90's Electronic Engineering this circuit can be used to measure phase angles between two signals from 0 to 180 degrees. The components used admit modern equivalents.
This filtered High Side sensor circuit was found in a 2005 Linear Technology application manual....
This circuit was found in a 1969 Mullard publication. The transistor may be the modern equivalent...
This circuit was found in an old Hewlett Packard publication. Its purpose is to activate neon...