query: When did Fender produces their first guitar amp?
passage: Fender amplifier
Leo Fender began building guitar amplifiers before he started manufacturing electric guitars. The first of these were the K&F models, produced between 1945 and 1946. The early K&F and Fender amplifiers relied upon vacuum tube circuitry, with the company adding solid-state models in the late 1960s.
passage: Bass amplifier
When the Fender company invented the first widely produced electric bass guitar (the Fender Precision Bass) they also developed a bass amplifier, the Fender Bassman, first produced in 1952. This was a 26-watt tube amplifier with a single 15" speaker. In 1954, the Bassman was redesigned to use four 10" speakers. This speaker cabinet was an open-back design; as such, it had poor low-frequency efficiency and was prone to blowing speakers when used for bass because of the lack of damping. Somewhat ironically, it became very popular as an electric guitar amplifier. The circuit design also underwent repeated modifications. The "5F6A" circuit introduced in 1958 is regarded as a classic amplifier design and was copied by many other manufacturers, such as Marshall.