The Fleming Oscillation valve was the first commercial thermionic device. It is the production product from discovery of the diode action by John Ambrose Fleming in October 1904.
This device is a diode that was to be used to rectify radio oscillations and thus act as a detector. The diode was not very sensitive and did not supplant the Cat's Whisker detector.
The construction is like that of a light bulb. The filament connects to two metal rods that pass to the base. The rods open in a 'V' shape and the single thread tungsten filament is a short arc between the rods. In use the 4.0 Volt filament would glow brightly as any lamp would. The anode cylinder surrounds the filament and is fluted at the top and bent in to partially close over the filament. The anode is connected through the side wall of the bulb to a silk covered wire.
The balloon envelope is 32 mm in diameter and, tip to tip is 72 mm tall.
References: Observation. Type Fleming was first introduced¶ in 1904.