1968 AMPEG B15-N
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In late 1968 major changes were made to the B-15. The chassis was now bolted to the lid and changed to black painted steel with aluminum front control panel. The front graphics became blue silcscreen or "blueline". A second input jack was added to channel two, both channels had normal and bright inputs. Black plastic ultra-hi and ultra-lo rocker switches were added. The polarity and power switches were now black plastic. A small red power light was added between the switches. The metal standby switch moved from the front to the back panel left side. The serial number was now stamped onto the back of the chassis top right. A two prong power outlet was added onto the back of the chassis. A white Linden New Jersey logo was silkscreened onto the back of the chassis. The plexiglass logo was discontinued. The new logo was the metal "a" bullseye plate, positioned on the speaker grille. The speaker cabinet became taller with a vinyl handle on each side, warranty.
Other 1968 characteristics: Round black D shaft knobs with silver tops, CTS potentiometers, two large black transformers, black tube cage protecting the tubes and capacitors, fuse, two prong power cord, schematic, 4 pin XLR speaker cable and jack, 4 chrome lid latches, vinyl covering, 15 inch CTS speaker, matching dolly with wheels.
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. 1968 serial numbers ranged from 075000 to 080000. For more precise dating cross reference the serial number with the amplifier's transformer, potentiometer, capacitor, speaker codes and covering.