Early vacuum tubes often featured unconventional designs, such as conical anodes, primarily to circumvent existing patent restrictions. Lee de Forest patented the Audion triode in 1907, with patents remaining active until approximately 1925. These early devices were gas-filled and initially used only as radio detectors.
Companies like General Electric and Cossor employed unique electrode shapes to bypass legal hurdles. Cossor, a London-based manufacturer, produced the R-type triode for military use. Their 1920s series, including Point One and Stentor models, utilized conical anodes, which were marketed as superior for performance and durability.
Despite the marketing claims surrounding the conical design, these tubes offered average electrical performance. Their reliability was largely attributed to high manufacturing standards rather than the shape of the electrodes. Cossor eventually abandoned the conical anode design due to production complexities and competitive pressure.
The Point One series featured a 2-volt V-shaped filament, while the Stentor series used a 6-volt W-shaped filament. Variations in voltage requirements for the Point One series were often indicated only on paper labels, reflecting the inconsistent manufacturing standards of the era.
