I have a Sparton Equasonne, not sure of model number. The one I have has three chassis assemblies. The set came with Cardon (brand name) 285 tubes; the sockets are marked 285/250; a 1937 Sylvania tube manual lists the 50 as a substitute for 285. Other tubes are Cardon 484 or 483 (I do not remember). The Equasonne has a unique circuit. Although some later sets used another tube, the set I have has the antenna feeding a tuner assembly consisting of a four gang variable condenser and four coils - no tubes or other components. After this 'tuner', there are five stages of untuned RF amplication, and a detector. Beautiful solid walnut cabinet, wood dors over the radio, some hand-painted detail, and a significant amount of carved wood (not repwood). The 250 (50)tube was used briefly in other sets, such as some Grundig-Majestic and other high-end sets. Hams used it, which may explain why there are not many floating around. The 250 (50) was short-lived, as the (2)42, (2)47, and later the 6L6 soon became the tube of choice for high output audio. The 250 / 50 is a triode which can run at high plate voltage, and it is pretty finicky, and has a short life span before the filament loses emmissability. Transformer input coupling must be employed, and the tube is easily ruined - disconnecting the speaker, etc. Some Sparton Equasonne used 183 or 182 tubes; do not substitute with a 71A. And do not replace a 384 with a 27; I have seen it done - wrong filament voltage.

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