Electronic components such as transformers, potentiometers, speakers, and some capacitors are often stamped with a date code, which indicates the manufacturer and the manufacturing date.
The code follows the format: = a number from 1 - 52 indicating the week of manufacture.
You should be able to find a number stamped somewhere on the speaker’s frame.
The format may look like this: 220 637 Here the number 220 designates the speaker as a Jensen, and 637 indicates a production date of the 37th week of 1956 or 1966.
The following chart, was originally printed in VG magazine, by Gerald Weber.