1967 AMPEG B15-N
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The Blue Check vinyl covering transitioned to a smoother grained texture. Silver trim was added around the grille cloth (after serial #060300). The grille cloth now had a shinier, finer grain. The black stove knobs changed to round black with silver tops and set screws manufactured by Romar of St. Charles, Illinois.
Other 1967 Portaflex characteristics: Chrome chassis shock-mounted onto the lid, white silkscreened graphics, two channels with guitar and bass input jacks on channel 1, three metal switches, two large black transformers, black tube cage protecting the tubes and capacitors, light up plexiglass logo, serial number stamped into chassis back lower left, fuse, two prong power cord, schematic, handles, 4 pin XLR speaker cable and jack, 4 chrome lid latches, chrome script logo, warranty sticker inside cabinet, 15 inch CTS or JBL speaker, matching dolly with wheels, protective vinyl amp cover, literature.
The second serial number system was implemented in January 1965 and used until the end of 1969. These are 6-digit numbers which appear to have been applied sequentially, but are not date encoded. 1967 serial numbers ranged from 049000 to 075000. For more precise dating cross reference the serial number with the amplifier's transformer, potentiometer, capacitor, speaker codes and covering.