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Otis Moorhead started his tube manufacturing business in 1916, making one of the copies of Cunningham's AudioTron, which he called the Electron Relay. He also made tubes under contract to the US and British Governments during WWI.

After the war, the ongoing patent wars between DeForest (owner of the grid patent) and Marconi (owner of the Fleming diode patent) rendered the legal manufacture and sales of tubes nearly impossible. Occasional deals were struck, however, and it was under one of these agreements (in 1919) that Moorhead was able to manufacture valves with the limitation that they licensed only for 'Amateur and Experimental' use.

Joe Gruber has supplied a series of articles, these are:

Joe's own article on Moorhead tubes can be found here.

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