The 8AR11 is a dual vari-μ RF pentode designed for IF amplification in television receivers. The 8AR11 is for 600 mA series heater chains and the 6AR11 is for parallel heater connection.
The main image shows the sections to be identical.
One section looking along the line of the grids. The screen grid can be seen wound on a bright rod. The anode is two vertical plates connected by the strap in the foreground. The dark structure behind the anode strap is the beam forming plate. The construction is as a beam tetrode not a three grid pentode.
The GE logo and the word Compactron has started to rub off.
The dome internally has the getter and externally the etched Type designation and country of origin.
The wide glass tube envelope is mm in diameter, and excluding the base pins is mm tall.
Reference: Datasheet. Type 8AR11 was first introduced in 1967.