Dating guitar amp transformers
The only date codes that seems to be readily available is found on the speaker magnet located under the bell cover.
The Ampegs made between 19 did not have serial numbers and must be dated in the same way as the Michael-Hull models, specifically, by finding the EIA date codes on pots, transformers, multi-section "can" capacitors, and speakers.
It is important to note that parts do not always contain EIA codes, especially those parts from the late 1940s and early 1950s.
Some common manufacturer codes for parts used in Ampegs include: The Michael-Hull amplifiers can be narrowed down to a date of manufacture between 19.
A Super Echo Twin with serial number 404553 was made in 1964 (4), during April (04) and may have been the 553th amp made that month (553).
Likewise, an Ampeg from 1954 would not be covered in blue check vinyl whereas an amp from 1964 would have this covering.
It has a note at the top of the page that they were reprinting with permission from the authors of Ampeg: The Story Behind the Sound, ©1999, published by Hal Leonard.
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These codes have been used on components including potentiometers (pots), transformers, capacitors, tubes, and speakers.
The code usually consists of 6 or 7 digits such as 137634 where the first two or three digits is the EIA code for the manufacturer (137 denotes CTS), the fourth digit and sometimes fifth digit denotes the year (in this case it could be 1956, 66, or 76), and the last two digits denote the week of the year.