This exhibit is a mystery. The design and paper label do not match the Cleartron Valves that we hold. The envelope is completely silvered making the inside invisible. The only defining feature is the term Mirilium Cathode and we can find no information on this.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 87 mm tall.
Updated July 11, 2014. shape:balloon construction:pinch type:triode base:b4 pins:4 pin:1.a pin:2.g1 pin:3.f pin:4.f