This exhibit has lost all identification. The style of the base cap and envelope all indicate a Dario product from the 1920s. The Universal Bivolt looks identical.
The anode is horizontal and the four visible supports are typical of triodes of the period with a single V for the filament. Powering the filament at 1.8 Volts gave a consumption of exactly 0.1 Amp. Looking at the advert gives only two possible Types - Universal or Resistron.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 87 mm tall.
References: Observation and test.
Absolute Maximum Operating Conditions¶
Updated November 20, 2017. shape:balloon construction:pinch type:triode age:1920.1930 base:b4 heater:2.0v pins:4 pin:1.a pin:2.g1 pin:3.f pin:4.f