Mfr radio dating
They generally follow the following format: (example) 322 5904 where 322 is the manufacturer code (in this case Tungsol), 59 is the year (1959), and 04 is the week.
One alternate scheme is: 274 940 274 is the EIA code (RCA) 9 is the last digit of the year (in this case 1949).
Code formats were not completely standardized, but a little deciphering will generally yield the info of interest.
Note that many makers also stamped OEM (Original Eqipment Manufacturer) part numbers above or below the EIA code, in some cases parts makers or the customer elected not to include the EIA codes, so not all parts have them.
Note that U - Z generally (but not always) as the only character, or last character, are used for rectifiers Final number: Element count The number of elements in the tube, the filament counting as 1. AND UNITED-ELECTRONICS WAS OUT OF BUSINESS IN 1988!
For example, the 6SN7 has two cathodes, two grids, two plates, and a filament. SO 88-37 WAS UNITED-ELECTRONICS INTERNAL NUMBERING SYSTEM AND DID NOT SIGNIFY ANY MANUFACTURING DATE.
Usually single digit date codes are from the 1940's, but have on occasion shown up in later decades, even up to the 1970's.
This list is circa 1955, and some codes have been reassigned or added since that time.
In years past, EIA (Electronic Industries Association) also went by the name of RETMA, and the original acronym of RMA (Radio Manufacturer's Association).
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This white sticker is located on the front side of some wireless product PCB's.
Examples: 6SN7GT: Filament rating is between 6.0 - 6.9V, SN=sequence code, 7 elements, glass tubular envelope. I personally have researched this in the past, and have come up with the theory that JHS was chosen by Sylvania meaning Joint Havells Sylvania or J. It has plants throughout Europe, Asia, North Africa and Central and South America, and is one of the few lighting companies that produces both lamps and lighting fixtures. Founded in the early 1900s as a business that renewed burned-out light bulbs, Sylvania and its predecessor companies ultimately began producing new lamps and then vacuum tubes for the radio industry.