1978 AMPEG B15-N
For photos, click on the links below:
1978 Portaflex characteristics: Black painted steel chassis bolted onto the lid, aluminum front control panel, black silkscreened graphics with rounded corners, two channels with normal and bright input jacks, white plastic tone adjustment rocker switches, round black D shaft knobs with silver tops, CTS potentiometers, white plastic standby and power switches, small round red power light, two large black transformers, black tube cage protecting the tubes and capacitors, serial number stickers, fuse, three prong power cord and outlet, no polarity switch, hardwired speaker cable with 1/4 inch jack to match the speaker input jack, Selmer logo silkscreened on back panel right side, schematic, vinyl handles on top and sides of speaker cabinet, 4 chrome lid latches, vinyl covering, plastic "a" bullseye logo positioned on the silver grille cloth, 15 inch speaker, matching dolly with wheels.
1978 Ampeg serial number dating is undocumented and very difficult. For more precise dating cross reference the serial number with the amplifier's transformer, potentiometer, capacitor and speaker codes.