In 1964 Fender introduced the AA864 circuit, and changed the appearance to the "Blackface" design, with black tolex covering and a black painted control panel. Fender was sold to CBS in 1965, and the AA165 circuit was briefly introduced, before being replaced by the AB165 circuit. The "Blackface" design continued until the "Silverface" model was introduced in mid 1967. Early "Drip-Edge" Silverface Bassmans made in mid 1967 used the same AB165 circuitry as the previous Blackface versions. The Brownface, Blackface, and Silverface "piggyback head" (except the Bassman 10 and 20, which were also combo amplifiers) versions of the 1960s, 1970s, and early 1980s generally followed a trend toward cleaner sound and more headroom.