Found in a 1969 documentation, this circuit for the 20 MHz band does not use a transformer. The circuit is a phase detector that makes use of the transistor of the time.
This circuit was found in a 1980s documentation for amateur radio. The circuit makes use of...
This circuit uses an operational amplifier to modulate the light emitted by an LED with audio...
This two-transistor circuit was found in a 1966 US documentation. The power transistors are of the...