Found in documentation from 1924, this 4-tube circuit has a heterodyne amplifier, as it was called.
This 1/2 hertz high selectivity filter was found in the December 1990 issue of Radio Electronics...
The two power steps below are intended for use with the SAA1027 stepper motor control but can be...
This interesting circuit, found in a 1986 publication, includes a powerful audio amplifier. Being...