Torridly-wound transformer, providing continuously variable AC voltage 0-15% above input supply voltage, selectable via a knob mounted on top. Normal operation in the voltage range 220-240 V AC gives a max. Voltage of approx. 4A. A carbon roller-brush rotates around the toroidal coil, providing the required output. A scale is calibrated along the circular knob 0-270 X 2V. With 3-core mains cable, socket terminals for output, and ON/OFF indicator.