The Western Electric 216A was first made in 1922 and used in the WE7A amplifier. The filament rating of 5.5-6.0 Volts was designed to be operated from lead acid accumulators without the need for a variable dropping resistor.
The 216A differs from the 101D or the UK made 4101D only in the filament rating. Like the 4101D the Type designation is pressed into the wax filling of the base shell.
This exhibit has the Type designation on the base shell. Early examples used base shells from the 101D. Later versions had black plastic bases.
The M shaped filament has a ladder grid and corrugated anode on either side. The anode clamps around the pinch stem. The type UV base has bayonet fixing and the locating pin can be seen here.
The filament is held by rigid hooks not springs.
The anode plates are held at the top by clamping to a rectangular ceramic insulator. Other supports also share this ceramic block.
The corrugations add rigidity to the thin anode metal.
The balloon envelope is 59 mm in diameter, and excluding the UV base pins is 102 mm tall.
References: 1047 & 3003. Type 216A was first introduced in 1922.