WD-11


The WD-11 vacuum tube, a triode, was introduced by the Westinghouse Electric corporation in 1922 for their Aeriola RF model radio and found use in other contemporary regenerative receivers including the Regenoflex and Radiola series.
The WD11 and "RCA-11" have the following characteristics:

Drawbacks

The WD-11's design was somewhat ill thought out, when the filament burns out it has a tendency to contact the plate, feeding high voltages back through the heater circuitry. 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.

Collectiblity

Because of its rarity it has become one of the most valuable vacuum tubes in the world. New-old-stock units have sold for as much as US$180 and used tubes for over $100, more than the original price of the radios that use them. Collectors rarely, if ever use these tubes for fear of burning them out.

Substitution

Sets that use the costly WD-11 and UX-199 tubes can be modified to use the 1A5/GT octal power pentode by wiring a 5.1 ohm resistor between the pins of the filament and fabricating an octal-to-four pin adaptor. The pin for the 1A5's suppressor is left unconnected and the screen connected to the plate.
The type 12 is electrically identical to the type 11, but with a more common UX4 base.