The 6B4G is an unusual valve in that the envelope holds two triode valves that are hard wired in parallel. This was the American answer to the PX4 and the parallel construction enabled the AC anode resistance to be the low figure of 800 Ohms. The device is rated at 3.2 Watts.
The filament is coated ribbon formed into an inverted 'w' in both anode cavities. The grid is a wire zig zag held on notched rods. The anode is formed of two pressed plates fixed together each with two half cavities. The anode cavities are 20 mm x 4 mm x 30 mm high.
The coating on the glass obscures the inner structure but the mass of wires leading from the pinch can be seen.
The top mica shows the twin triodes. The oxide coated filaments are both dual inverted V shapes and held in tensioning springs.
The classic envelope is 49 mm in diameter and, excluding the IO base pins, is 111 mm tall.
References: Data-sheet & 4040. Type 6B4G was first introduced in 1937.