This analog frequency meter for low frequencies was found in Radio Electronics magazine from July 1958. The circuit has several scales with the frequencies indicated in the diagram.
This circuit was found in a 2006 documentation. Its purpose is to control a servo system in which...
Raytheon's used operational amplifier is rare today, but the configuration can be adapted to use...
This alarm, from a 1996 magazine, can be fitted with two BC548s in the original configuration...