Stamped on the metal backing of most amps is the serial and production number. The following list, compiled by Greg Gagliano, establishes dates through 1976: A00100 to A01200 - 1964 A01200 to A04300 - 1965 A04300 to A07000 - 1966 A07000 to A10400 - 1967 A10500 to A11300 - 1967 A10500 to A16500 - 1968 A16500 to A21400 - 1969 A21400 to A25600 - 1970 A25600 to A37000 - 1971 A37000 to A50500 - 1972 A50500 to A68000 - 1973 A68000 to A99999 - 1974 A81000 to A99999 - 1975 B01000 to B15000 - 1975 B15000 to B68000 - 1976 If these steps are unsuccessful, a number of books have been published that help to date amps based on part codes.
Two different colors of grillclothes were featured on the blondes, oxblood and wheat.
The brownface amps originally featured a dark maroon or "oxblood" grillcloth, which was changed to "wheat" in 1962-63.
The Brown amplifiers included all of the all-in-one combo amps except the flagship Twin and Vibrasonic, and the little Champ which retained its "tweed" (twill) covering.
Fender amplifiers began making a name for themselves with the Tweed series, so called because of their cloth covering, which is actually varnished cotton twill (tweed is a coarse woollen fabric, commonly used for jackets, coats and caps; it is often woven in a twill pattern, which is likely the reason for the confusion over naming.) They were produced for more than a decade and are now eminently collectible and praised for their sound quality.
The twill was first used in 1946 on the Dual Professional a twin 10" 6L6 powered model of which only 400 were made before being renamed "the Super Amp" in 1948.