Radio Receiver Power Cables
These power cables came in different lengths. Radio receiver cables had a standard configuration with 6 connecting pins. Both the male and female plugs had special grooves on them to prevent plugging into a device which used a different voltage, thereby damaging the device. The female plug was attached to the radio receiver, while the male plug was attached to the power supply. Two of the six pins supplied the filament (heater) voltage (+,-), Anode (grid) voltage (+,-), one pin for the +Umf and one pin for Ground.
Here is a standard 1 meter radio receiver power cable.
This is the radio receiver plug. Note the grooves on the side of the plug. Many military radio receivers had corresponding grooves on their power receptacles to prevent a transmitter power cable to be accidentally inserted.
This is the power-supply plug. Note the grooves on the inside of the plug cowl. Both ends of this cable can be connected together.