This exhibit is a two Volt LF valve branded Barum. This brand is not listed by Thrower and does not appear on the Internet, thus it is a mystery. More information please.
The filament is open circuit but it probably ran at 0.1 Amp. The gettering obscures the construction but the anode can be glimpsed as a horizontal box and looks like the The Philips-Mullard (PM) Series style of valve.
The base has a ridge to denote the anode pin and the base pins have helical slots rather than straight cuts.
Another view of the base pins. The connection wires solder at the tip of the pin.
The etched lettering on the dome is difficult to make out but has the 2V , LF and name Barum.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 92 mm tall.
