Most unusually we know the maker's name but not the Type. With the BA2 the Type is printed within the identification label not so here.
The envelope is metalised and the fixing of the wire can be seen. The base is B5 suggesting either a battery screen grid valve or a mains triode. The paint covers all of the glass and thus no internal inspection is possible.
The reverse is without any marking.
The balloon envelope is 45 mm in diameter, and excluding the B5 base pins is 99 mm tall.
Updated November 21, 2016. shape:balloon construction:pinch age:1930.1940 base:b5 pins:5 pin: