The U12 directly heated full wave rectifier was a popular design that was also produced by other manufacturers.
Initially the U12 and the U14 were the same valve. However, some valves performed better than others on final factory test so the best ones were graded and marked U14 whilst the also-rans were marked U12.
The M-OV ellipse with the Type designation is on the envelope but the image is feint. Identification has been scratched into the base cap.
The Marconi brand label.
The mesh anode allows a view of the inverted V ribbon filament within. The filament tension spring for one rectifier can be seen above the mesh.
The classic envelope is 49 mm in diameter and, excluding the B4 base pins, is 106 mm tall.
References: Data-sheet, 1040 & 1043. Type U12 was first introduced in 1931. See also1931 adverts.
