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The EIA source-date code is a numeric code, assigned and registered by the EIA.
These codes often overlap within a few months to as much as a few years when used to determine the originality of a particular vintage guitar or amp.
The best way to date your vintage guitar or amp is from the manufacturers serial number and then use this guide as a reference to date the parts that make up said guitar or amp.
Dates and source codes to help aid and determine the age or year of production of your vintage guitar,amp or other electronic instrument. Source-Date Codes On American made vintage guitars and gear, the pots and speakers provide an excellent opportunity to date a piece of equipment by referencing their "source-date code".
The source-date code found on pots and speakers gives the manufacturer and date (roughly) when the components were made.