The circuit shown was found in the 1994 National Semiconductor's Linear Application Handbook. The op amp admits equivalents and the power supply must be symmetrical.
An E or AND gate can be constructed based on common diodes. In the case, the diodes are for...
In the figure we have a simple signal tracer circuit to be coupled to the volume control of an AM...
This circuit for analog instruments was found in a Raytheon documentation from the 1960s....