This circuit was found in the June 1991 issue of Radio Electronics magazine. The circuit uses two Hall effect sensors of the time. It can be assembled using modern equivalents.
The load controlled by this circuit depends on the triac used. The circuit is from Electronics Now magazine...
The operational amplifier of this low current source may be any of the JFET type. The output...
This stage was used in old audio ampliiers and radios from the 1950s and 1960s. It uses one of the...