The 12Z3 is a half wave rectifier and was designed primarily for use in domestic equipment without mains transformers and American mains supplies.
The 14Z3 is electrically the same but on a B8B loctal base.
The anode is mesh.
The insulated heater is connected at top and bottom suggesting a single wire. The cathode tube is oxide coated and can be seen through the wire mesh of the anode.
Radiomuseum.org quote 1933 for first introduction but Thrower has a date of 1936. Heater voltages aligned with lead acid storage batteries appeared in the mid 1930's.
The wide glass tube envelope is 29 mm in diameter, and excluding the UX4 base pins is 87 mm tall.
References: Data-sheet, 1040 & 3002. Type 12Z3 was first introduced in 1933. See also1933 adverts.
