The HL210 is without markings on the envelope or base. The pinch has HL210 written on it. The HL210 was made by Mazda and M-OV The spiral base pins on this exhibit match those used by Lissen.
An unusual Bakelite base and unusual spiral split pins.
The close-up shows two sets of support rods. The inner pair hold the filament ends. The base of the single V is held below the anode box.
The balloon envelope is 42 mm in diameter and, excluding the B4 base pins, is 94 mm tall.
References: Data-sheet. Type HL210 was first introduced in 1929. See also1929 adverts.
