Zenith 6D317, 1939 | From a 1939 Zenith brochure. | |

Approximately 14 inches / 356 mm wide. Tube complement: 6A8G mixer/oscillator, 6K7G IF, 6Q7G detector, 25L6G audio output, 25Z6G rectifier, 100-70 ballast. As shown in the brochure excerpt above, this radio was also available as model 5R317, which came with a five-tube (no ballast), AC-only, transformer-powered chassis. |

About Zenith model numbersZenith model numbers reveal a lot of information to the collector. From the early 1930s to at least the mid-1950s (the date limits of my attention), Zenith used three different model-numbering schemes. From the early 1930s through 1935, Zenith used two- and three-digit numeric model numbers. Generally, the greater the number, the later the radio. In 1935, models appeared with 800- and 900-series model numbers. Starting in late 1935, Zenith began adhering strictly to the model year concept. This means that model changes were generally made once per year, and the new models were introduced in late summer or fall. When Zenith introduced its 1936-model-year radios in late 1935, they began using a very descriptive model number of the form XX-A-YYY. In this new format, 'XX' is a one- or two-digit number indicating the number of vacuum tubes on the chassis (eye tubes, rectifiers and ballast tubes included, of course). 'A' is a single-letter descriptor that tells about the radio's capabilities—if it's AC or battery powered, what bands it tunes, etc. For example, the D in the model number of the radio on this page means that it is an AC/DC broadcast-band-only set, and the commonly appearing S means that the set is AC-powered and has at least one shortwave band. The first digit of the 'YYY' part of the model number indicates the radio's model year, as follows:
- a missing first digit (i.e., a two-digit 'YYY' segment): 1936 model year
- 1: 1937 model year
- 2: 1938 model year
- 3: 1939 model year
- 4: 1940 model year
- 5: 1941 model year
- 6: 1942 model year
- 0: 1946 model year
- 7: 1947 model year
- 8: 1948 model year
- 9: 1949 model year
At the start of the 1950 model year, Zenith again changed its model-numbering scheme, this time to a less descriptive one. The new model-number format is AXXX, where prefix letter 'A' indicates the model year. I haven't been as attentive to this period as the previous one, but I have at least learned that the following is true regarding the prefix letter: - G: 1950 model year
- H: 1951 model year
- J: 1952 model year
- K: 1953 model year
After 1953, things got more confusing, with multiple prefix letters being used in a single model year. Perhaps there's a pattern, but I'm not interested in these years so I haven't attempted to decipher it. |

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