Listening #61 Dating Decrepit Drivers
Decades ago, the Electronic Industries Alliance established a source code for manufacturers to use on various finished components: potentiometers, transformers, large capacitors, and the like. I learned about it during the years when I was still buying and collecting electric guitars and amplifiers, and more than once, the code kept me from being burned. (Nothing screams unoriginal quite as loudly as a 1956 Fender tweed Harvard amp with volume and tone controls from the years of the Nixon administration.)
The EIA code is also a boon to anyone just getting into vintage hi-fi, and it's especially easy to use in the dating of older loudspeaker drivers. Through most of the 1960s, a six-digit code was stamped somewhere on the back side of every driver frame. The first three digits were always the manufacturer's code: Altec was 391, Jensen 220, Utah 328, General Electric 188, Electro-Voice 649...and so it went.
The fourth digit usually corresponded with the last number of the year of manufacture—you have to guess as to the decade—and the last two digits are the week of manufacture.
By the end of the 1960s, the code got longer, making room for the last two digits of the year, among other things: manufacturing plant location, work-shift number, and the like. Needless to say, there are and have been a great many more three-digit codes from a great many more manufacturers; they and other pertinent data can be easily found by doing an Internet search on the words EIA date code.—Art Dudley