The markings on this exhibit have become illegible. What remains etched into the envelope is a Union Jack flag. Above the flag is clearly the word British. Below the word starts with 'St' and the rest is not clear but is believed to be Standard. The main picture shows the side not silvered by the firing of the getter and so the electrodes can be seen.
The valve is a directly heated triode.
On the silvered side of the envelope can be seen this etched flag logo.
The balloon envelope is 46 mm in diameter, and excluding the B4 base pins is 92 mm tall.
Updated April 30, 2013. shape:balloon construction:pinch type:triode age:1920.1930 base:b4 pins:4 pin:1.a pin:2.g1 pin:3.f pin:4.f