The 'Electro' Audion. Hugo Gernsback sold these valves from 1911 to 1913. The manufacturer of the valve was McCandless of New York. Gernsback did not just sell the bulb, as they were called, in the original box but mounted the valve in a socket fixed to an insulating board. This board also featured five terminals to which the leads of the valve were attached. The complete assembly was sold for $5.00.
The sales records for the McCandless company show the Gernsbeck's company purchased 104 audions in 1911, 156 in 1912 and 211 in 1913. McCandless made valves for DeForest at this time as well.
All of these images featured in an ebay advert.
The top view of the insulated base.
The underside of the base showing wires from the candelabra base to the terminals.
The bulb with glass pinches at top and bottom. The insulation on the wires from the top of the valve has degraded badly.
The electrodes: the double filament can be seen. This early audion design was used as a detector. It was only in 1911 that DeForest demonstrated amplification and several years of research by Western Electric et al was required to make the soft audion into a hard vacuum triode.
The balloon envelope is 48 mm in diameter, and excluding the base pins is approx 90 mm tall.
Reference: 1047. Type Audion was first introduced in 1911.