The 6EA8 is a triode pentode. This valve was made by Mullard for the American distributor IEC.
The pentode is of the sharp cut-off type. The design purpose was as a triode oscillator and pentode mixer within VHF TV tuners.
The warm-up time is 11 seconds and this valve would usually be found in a series heater chain.
The triode is on the left. Both sections have copper supports for the control grids. On the right the suppressor grid winding can be seen and almost obscured by the anode is the tips of the screen grid winding.
Looking along the axis of the pentode at the suppressor grid.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 47 mm tall.
Reference: Datasheet. Type 6EA8 was first introduced in 1958.