1965 AMPEG B15-N
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Later in the year Ampeg discontinued the serial number sticker inside the speaker cabinet and started stamping the serial number into the back left hand side of the shock-mounted chrome chassis. During the year the tilt back rod was discontinued.
Other 1965 Portaflex characteristics: White silkscreened graphics, two channels with guitar and bass input jacks on channel 1, black stove type knobs, CTS and Centralab potentiometers, three metal switches, two large black transformers, black tube cage protecting the tubes and capacitors, light up plexiglass logo, fuse, two prong power cord, schematic, handles, 4 pin XLR speaker cable and jack, 4 chrome lid latches, chrome script logo, Blue Check vinyl covering, silver grille cloth, 15 inch speaker, matching dolly with wheels, protective vinyl amp cover, literature.
The first serial number system are 6 digits in length with the following pattern: YMMNNN, where Y denotes the year, MM the month, and NNN the # unit produced that month. The # 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. Nevertheless, for dating purposes, the serial number provides adequate information during this period. For example, an amp with serial number 404553 was made in 1964 (4), during April (04) and may have been the 553th amp made that month (553).
The second serial number system was implemented in January 1965 and used until the end of 1969. This system overlapped with the previous serialization scheme for a period of about 6 months. These are 5 or 6 digit numbers which appear to have been applied sequentially, but are not date encoded. 1965 serial numbers ranged from 000001 to 020000. For more precise dating cross reference the serial number with the amplifier's transformer, potentiometer, capacitor, speaker codes and covering.
However, caution is needed for dating amps from 1965, as the serial numbers from this year were already used in 1960. A serial number 009054 could be from September 1960 or it could be from the second serial number system implemented in 1965 (above). The key is the model and the cosmetics. For instance, an Ampeg from 1960 would be covered in navy random flair vinyl whereas an amp from 1965 would be covered in blue check vinyl. Another check for a 1960 versus a 1965 or later serial number (i.e. numbers beginning with 0) is that the second and third digits of the number denote the month in the first serial number system. Therefore, a serial number where these two digits are greater than 12 must be from the second serial number system (1965-69).