The Type 30 is a general purpose amplifier triode. It is directly heated for use with battery supplies. The 2.0 Volt filament was for use with a lead-acid accumulator.
The low power power triode does not require a blackened anode for more efficient heat radiation but the thin nickel sheet is ribbed for mechanical rigidity.
The front support rod holds the filament tension spring wire. The filament can be seen to be a single inverted V.
The classic envelope is 38 mm in diameter and, excluding the UX4 base pins, is 87 mm tall.
Reference: Data-sheet. Type 30 was first introduced in 1930. See also1930 adverts.