1975 Ampeg V4-B
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1975 V4B characteristics: "Blackline" silkscreened graphics, aluminum D shaft knobs, two input jacks, black rocker switches, three metal power switches, two small round power lights, silver grille cloth with no badge logo, three prong power cord and outlet, fuse, white silkscreening, Magnavox manufacturing, serial number sticker on the back, impedance switch, two metal cord wraps, black painted chassis, transformers, tubes, capacitors, vinyl handle, black vinyl covering applied over black painted wooden box, four rubber feet, four chassis connector bolts, literature.
Ampeg serial number dating is undocumented and very difficult. Some examples of 1975 Ampeg serial numbers are 2662x, 4904x, 5687x, 6941x and 7278x. For more precise dating cross reference the serial number with the amplifier's transformer, potentiometer, capacitor and speaker codes.
Other codes to determine the manufacture date: The large power transformer should have a six digit code stamped into the metal. The first three digits indicate the company's personal manufacturing code. Those should be 682, which indicate the Electrical Windings Company. The fourth number indicates the year. The fifth and sixth numbers indicate which week of that year.
Potentiometers are also date encoded. There is a seven digit code stamped into the metal. Again, the first three digits indicate the company's personal manufacturing code. Those should be 137, which indicate Chicago Telephone Supply or CTS. The fourth and fifth numbers indicate the year. The sixth and seventh numbers indicate which week of that year. Capacitors and speakers can also be dated in a similar manner.