The DEP215 is a four pin triode from Osram that has internal metalisation obscuring most of the internal construction. The advert linked above shows the horizontal box anode with two parallel filament threads within the grid.
The balloon envelope is 43 mm in diameter and, excluding the B4 base pins, is 83 mm tall.
References: Advert & 1043. Type DEP215 was first introduced in 1927.
Absolute Maximum Operating Conditions¶
Updated October 05, 2018. 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