 It was replaced just a year later by higher performance tubes which were less likely to encounter this problem, Westinghouse Electric's WD-12 and General Electric's UX-199.No radios using the WD-11 tube were designed after 1924, RCA ceased production and issued a service bulletin describing how to retrofit existing sets to use the newer UX-199 triodes.Because of its rarity it has become one of the most valuable vacuum tubes in the world.