De Forest dual filament Audion vacuum tube, 1908

In 1906, inventor Lee de Forest improved upon fellow electronics pioneer Reginald Fessenden's vacuum tube, creating what he called the triode, or "Audion." After further experimentation in 1911-12, the Audion was used as a detector of radio signals, an amplifier of audio, and an oscillator for transmitting, making possible great advancements in transcontinental telephony and radio broadcasting. This rare dual tantalum filament de Forest Audion was handmade by  H.W. McCandless & Co. of New York (an automotive lightbulb maker) in 1908, the only year double filament Audion tubes of this type were made. The glass tube was mated to a standard candelabra lightbulb screw base. The grid is the usual zig-zag formation (made by bending wire between nails hammered into a piece of wood). The single plate has a single anchor wire. The filament supports come up from the screw base, rather from a glass press. The contact was soldered externally to the base to make contact. The base insulation is glass, rather than porcelain. The cap is tarred over, covering the exhaust tip.