It should bear an EIA code somewhere, Altecs begin with a 391, and are usually 6 digits total. The last 3 digits are your date code, the first number is the last number of the year, the last 2 digits are the week.
391236, in the case of an Atec tube amp next to me indicates the 36th week of 1972. In this particular case, i had to confirm the year as '72 by the date code found on the filter caps, and trim pots as the year could have been '62.
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