This circa 1903 "spade" responder (or electrolytic detector) is one of the best examples of Lee de Forest's several costly attempts to work around Marconi's and Fessenden's patents. A variant of Fessenden's electrolytic detector, it uses a flat piece of platinum leaf sealed into glass instead of Fessenden's platinum wire. De Forest's detector soon became standard quipment in de Forest wireless stations as well as U.S. Navy receivers. Fessenden successfuly sued de Forest, but by then de Forest had moved on to crystal detectors. Switches and/or knobs on top of the radio are labeled: Potentiometer, Battery, Shunt and Telephone. De Forest exhibited this apparatus as part of his display at the 1904 St. Louis World's Fair, along with a 300 foot high "De Forest Wireless Telegraph Tower."