This exhibit lacks all identification as to type. However, the underside of the base carries the Ediswan logo. The red line on the base indicates the anode pin. The pins themselves are of simple split-pin construction suggesting that this dates to the mid 1920s.
The ES logo and base pins. The internal construction is obscured but with a strong light and glass it is just possible to see that the anode is mounted horizontally.
The balloon envelope is 44 mm in diameter, and excluding the B4 base pins is 78 mm tall.
Updated October 23, 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