The BTH B3 is a dull emitter triode designed for general purpose applications. The electrode assembly is vertically mounted and the filament is a single strand of thoriated tungsten wire. Our exhibit has the filament intact and powers up to a bright orange glow.
This exhibit shows the getter as milky but not pure white and this suggests that the valve is 'soft' ie there is gas in the envelope.
The plated base shell is bright with no signs of pitting.
The electrodes were difficult to photograph through the milky envelope.
The balloon envelope is 37 mm in diameter, and excluding the B4 base pins is 90 mm tall.
References: 1003 & 1004. Type B3 was first introduced in 1924.