The anode is carbonised to improve heat radiation and the ridges give the thin Nickel sheet some rigidity. The DO24 designation is etched into the envelope. On the main picture the lettering reads filament volts 4.
The base of the anode. The etched lettering is visible showing the Mullard logo above the type designation. The filament is made of substantial wire. The grid appears to droop suggesting a less than tight winding.
The top of the anode. The support rods welded to the anode supports pass to two glass rods. The rod at to top of the image holds the filament tension springs. The rod at the lower edge of the picture holds the grid supports apart.
The top of the grid showing the lack of uniformity in winding and the oxide coated filament strands passing through the grid.
The balloon envelope is 67 mm in diameter, and excluding the B4 base pins is 150 mm tall.
References: Datasheet & 1043. Type DO24 was first introduced in 1931.