This circuit is from an American 1964 documentation. Transistors of the time are used, but modern equivalents can be employed.
Found in documentation from the 70s, this circuit uses an operational one from that time. It goes for...
This old 4-channel circuit was found in the December 1994 Electronics Now magazine. The circuit uses...
Found in a 1969 documentation, this circuit for the 20 MHz band does not use a transformer. The circuit is...