This simple circuit to monitor the frequency of the power grid uses an analog indicator. The adjustment trimpot can be 4k7 and the indicator is 100 mA full scale.
This circuit with SCR is from a Radio Electronics magazine from September 1965. It is a commercial...
This circuit was found in the July 1986 issue of Radio Electronics magazine. The circuit has a...
This circuit was found in a QST from the 1990s. The circuit expands the scale of a 10V instrument to...