The MHL4 was used in professional and military applications over many years until it was superseded by the L63, which had comparable characteristics.
The electrodes: the mesh anode and getter support at the top. The cathode is connected at the opposite end to the heater making a long path.
The mesh annular getter holder.
Another view of the electrodes. The support is only from the glass pinch.
The balloon envelope is 50 mm in diameter and, excluding the B5 base pins, is 114 mm tall.
References: Data-sheet, 1040 & 1043. Type MHL4 was first introduced in 1929. See also 1929 adverts.