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).Caution is needed for dating amps from 1953, 1954, 1955, and 1960.Ampegs can be divided into six distinct groups for dating purposes: pre-1953, 1953 to mid-1965, early 1965 to 1969, 1969 to 1979, 1981 to 1984, and post-1984.

A Mercury with serial number 009054 could be from September 1960 or it could be from the second serial number system implemented in 1965.

Luckily, it is very easy to determine which year the first digit denotes. For instance, the Super Echo Twin was made in 1964, but not in 1954.

The Nth unit, however, may not have started with 001.

Ampeg may very well have used 100 or 101 as the starting point during slow production periods.

It appears that the serialization system used during this time period is date encoded which makes dating the amplifier rather easy.

The serial numbers are 6 digits in length with the following pattern: YMMNNN, where Y denotes the year, MM the month, and NNN the Nth unit produced that month.

A final cross check with EIA dated components should remove any doubt about an made during the 1953 - 65 period.

The second serial number system was implemented in January 1965 and used until the end of 1969.

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.

The M-12 Mercury circuit of 1960 used 6V6 power tubes, but the Mercury circuit of 1965 used 7591As.