1962 AMPEG B15-N
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Other 1962 Portaflex characteristics: Chrome chassis shock-mounted onto the lid, white silkscreened graphics, two channels with normal and bright input jacks on channel 1, black stove type knobs, 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, CTS (Chicago Telephone Supply) potentiometers, one plastic or leather handle, 4 chrome lid latches, chrome script logo, silver grille cloth, serial number sticker, 15 inch Jensen speaker, tilt back rod, matching dolly with wheels.
The serial numbers 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).
For more precise dating cross reference the serial number with the amplifier's transformer, potentiometer, capacitor and speaker codes.