This circuit was found in a 1967 US publication. In it we have the implementation of a ring counter using only relays. Relay free contacts can trigger indicator lamps or LEDs.
This twisted pair exciter circuit uses 80's components. The circuit is from a documentation of the time, but...
This control for bass, midrange, and treble was found in the March 1995 issue of Electronics Now...
The SCR sector of this circuit can be powered by high voltage AC and instead of the LEDs we can...