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.
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. This exhibit has the shouldered envelope whilst the 12Z3 looks to be later with the tubular envelope.
The anode is made of wire mesh. At the top the heater wire can be seen to be coiled on a ceramic former and coated with ceramic insulation.
A closer view of the cathode and heater.
Where the getter material allows a view of the structure is possible.
The wide glass tube envelope is 39 mm in diameter, and excluding the UX4 base pins is 99 mm tall.
References: Data-sheet, 1040 & 3002. Type 12Z3 was first introduced in 1933. See also1933 adverts.
