This exhibit has split pin base pins and is fully silvered inside the glass. No identification of any type can be seen suggesting it once had a paper label around the base. It is possibly of Dutch origin.
The base shell and base pins.
Thanks to Derek L Widdowson for donating this exhibit.
The balloon envelope is 40 mm in diameter, and excluding the B4 base pins is 79 mm tall.
Updated July 30, 2015. 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