An electronic component called a vario-coupler, used in early vacuum tube radio receivers, manufactured by Ampco (American Pattern Foundry and Machine Co.), New York, from an ad in a 1922 radio magazine. The vario-coupler was an air-core RF coupling transformer with adjustable coupling. It consists of a coil of wire on a hollow cylindrical form, with a second coil of wire suspended inside on a slanted shaft. Rotating the shaft can rotate the inner coil so the angle between the axes of the inner and outer coil can be at any angle between 0° (parallel) and 90° (perpendicular), varying the coupling (mutual inductance) between the coils from maximum to near zero.