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 interesting circuit, found in a 1986 publication, includes a powerful audio amplifier. Being...
This circuit with JFET and Unijunction was found in an ancient American documentation. The...
This circuit brings together in a single set a preamplifier and an equalizer with several inputs. The...