The WD12 was designed by Westinghouse Canada and released in 1923 as the successor to the WD11 electrically they have the same characteristics. The difference is in the base, the WD11 has a four pin base and the WD12 has the UV base.
The RCA received designs and patents from the founding companies.
The WD12 is a high vacuum valve designed for use as an amplifier or a detector. and was one of the first hard valves available to the American experimenter.
The transfer on the brass base cap reads: To be used only for amateur experimental and entertainment use only to the extent indicated in the attached note. The UV base was of the bayonet type and the locating pin is seen on the left.
The vertical construction from the front.
The vertical construction from the side.
The grid support is on the right and the top filament connection is on the left. The anode support runs the length of the cylindrical anode.
The helical grid looks to be fixes loop by loop to the side support. The filament is a thin wire attached to the tape at the top.
The construction close-up.
The wide glass tube envelope is 30 mm in diameter and, excluding the base pins, is 91 mm tall.
References: Data-sheet (Tube Collectors Association), 3001 & 1047. Type WD12 was first introduced in 1923. See also1923 adverts.