The anode is much wider than the front to back dimension.
The top of the envelope carries the etched identification and makers name. The DO24 can just be seen.
The base of the anode and pinch. The horizontal separation of the electrodes is by means of a mica sheet. The earlier production in the balloon envelope used glass spacers and not mica sheets.
A close-up of the base of the anode. The grid wires are straight and under tension. The filament with the white oxide coating can be clearly seen.
The anode is made from thin sheet pressed to shape and ridged for strength. The outer surface is carbonised to improve heat radiation. Note the wire welded to the anode support that holds the bottom mica in place.
The classic envelope is 51 mm in diameter, and excluding the B4 base pins is 125 mm tall.
References: Data-sheet & 1043. Type DO24 was first introduced in 1931. See also1931 adverts.