If a component manufacturer is unable to use the four (4) digit code date, an alternate three-digit (3) code may be used by taking only the last digit of the year.Then 134-6320 would become 134-320 and the specifications of the instrument should be used for determining the approximate year or decade the particular instrument was built.
Specializing in guitar & amplifier repairs and restorations in New Jersey.
This is information from the Engineering and Publications department.
(made pots out of Raleigh, North Carolina) 328- Utah Sound Products/ Division of Oxford International, Ltd., Chicago, ILL. 579- Belden Wire and Cable/ Cooper Industries (makes various cable and magnet wire) 736- Sprague (now called Allegro Micro Systems, Inc.
381- Bourns Networks, (makes quality potentiometers, out of Logan, Utah) 416- Heath Company (made early test equipment kits and electronics) 465- Oxford Speaker Co./ Mc Gregor Loudspeaker Mfg. makes capacitors) The EIA Weekly Date Code always uses a two-digit number with week #1 starting with 01 to 52 and never higher than 52 weeks.
These are rough guidelines to help date your amplifier.