This exhibit was sold on ebay in October 2008 as a mystery valve. The unusual feature is the moulded base. This design can also be found on Stentor Two. The conclusion is that our mystery valve is a mid to late 1920s Cossor triode.
The moulded base and pin design match the Cossor products.
The valve is clearly a triode with four strands of oxide coated filament passing through the grid.
The general assembly from pinch to anode.
The anode is a mainly flat structure but is quite long. This length and four strand filament suggests an audio output valve for battery operation but at a higher rating than the Stentor Two or Stentor Four the four volt version.
The balloon envelope is 44 mm in diameter, and excluding the B4 base pins is 107 mm tall.