This circuit is from a Radio Electronics from April 1964. The circuit uses power transistors of the time, which must be mounted on a good heat radiator. Modern equivalents can be used.
Found in documentation from the 90's, this circuit has a narrow pass band around 1 kHz. The...
This circuit was found in a Radio Electronics magazine from November 1991. The circuit operates at 2.2...
Found in old documentation, this circuit has only the most difficult component to obtain the PUT....