Fifty years ago this month, the August 1970 issue of Popular Mechanics showed how to put together this somewhat ambitious project, a remote carrier-current speaker for your hi fi. A one-transistor transmitter was hooked to the output of your amplifier, and the receiver could be plugged in to any outlet in the house to listen remotely. The project also gave you an easy method of having an outdoor speaker, as long as you had an outdoor outlet. If desired, you could construct additional receivers for use in other rooms, all tuned in to the same transmitter. The speakers were equipped with individual volume controls.

To simplify the project, the receiver used a pre-wired audio amplifier available from Lafayette Electronics. The electronics all mounted in a small box that could be affixed to the back of the speaker.

Both transmitter and receiver used a standard 455 kHz IF transformer for their tuned circuit. These were tweaked to get them down to about 400 kHz, the frequency used by the system. That signal was transmitted through the power wiring. This “antenna” was coupled to the circuit on both ends through capacitors.

Transmitter schematic.

Receiver schematic.