This spherical audion has a flat nickel plate for the anode and a grid iron format for the grid and a filament formed as two loops. The base is candelabra and provides the filament connection. The grid and anode connections are covered by woven sleeves.
De Forest believed that gas was an essential component of the operation of a valve for amplification and so his valves were soft. Later it was shown that although less sensitive than the soft valves, the hard valve was more stable and reproducible and the TM and R valves replaced soft valves.
Looking across the electrodes. The valve is single sided, whereas the audion here is double sided with a single filament but two grids and anodes in parallel.
The back of the nickel plate anode.
The grid wire is folded to place seven lengths between the filament and anode.
The both filament loops have broken.
The grid wire has been discoloured by the heat from the bright filament.
Microscope image of the grid and filament. The fold in the support wire holding the filament can clearly be seen.
The balloon envelope is 52 mm in diameter, and including the candelabra base is 85 mm tall.
Reference: 1047. Type Audion was first introduced in 1911. See also1911 adverts.
