The Fender Bassman is a bass amplifier introduced by Fender during 1952. Initially intended to amplify bass guitars, the 5B6 Bassmanwas used by musicians for other instrument amplification, including the electric guitar, harmonica, and pedal steel guitars. Besides being a popular and important amplifier in its own right, the Bassman also became the foundation on which Marshall and other companies built their high-gain tube amplifiers.During 1952, the Fender 5B6 Bassman amplifier was introduced as a combo amplifier cabinet that included the amplifier chassis combined with one 15" speaker. The 1952–1954 5B6 Bassman amplifiers had two 6SC7 or 6SL7GT pre-amp tubes, two 5881 power tubes and a single 5U4G rectifier tube. It was designed to generate 26 watts at an 8 ohm impedance load, and offered a cathode-based bias.
From 1952 through the spring of 1954, Fender produced approximately 660 model 5B6 Bassman amplifiers (serial numbers #0001- 0660). The earlier cabinets have been called "TV Front" designs, with a front panel that had a rectangular grill cloth with rounded corners and looked much like a television of that era. In 1953 the cabinet designs were changed to the so-called "Wide Panel" design, with a 5 inch wide tweed covered panel above and below a wider swath of grill cloth. Fender ceased production of 5B6 Bassman amplifiers during the spring of 1954.
During November 1954, Fender introduced the newly designed 5D6 Bassman amplifier offering four ten inch speakers and was designed utilising two rectifier tubes. The 5D6 was a major departure from the earlier 5B6 Fender Bassman model. Designed by Freddie Tavares, longtime R&D man at Fender, the new circuit included two rectifier tubes and became known as the Dual Rectifier Bassman. Instead of the single 15" speaker, four 10" Jensen Alnico P10R speakers were used. The circuit had two innovations: a fixed bias for the power tubes, which increased power in comparison to the earlier cathode bias design, and a cathodyne phase inverter, using half of the 12AX7 tube and allowing a third gain stage on the other half.
Fender began making other models with tweed covering, a similar open backed cabinet with a rectangular grill cloth and a narrow (just over an inch wide) tweed covered panel at the top and bottom. Produced from 1954 until 1960, these models are called the "narrow panel" tweed amps .
Fender introduced the model 5D6 "DK" in November 1954 followed by the 5E6 Bassman Amp during early 1955. The 5E6-A Bassman model was introduced later that year and included some evolutionary improvements. Demand for the tweed Bassman amp grew, so Fender increased production{{citation needed|date=July 2013}}. By the middle of 1957 more than 1,500 examples of the 5E6 series had been sold.
In July 1957, Fender introduced the model 5F6 Bassman. This model also had four Jensen P10R speakers, but the power supply was redesigned around a single 83 mercury vapor rectifier tube, and a new preamp circuit was introduced that included a three knob tone stack, with separate controls for Treble, Mid and Bass. The power amp included a "long tailed pair" phase inverter, an innovation that noticeably increased the "headroom" or clean power output capability of the amplifier{{citation needed|date=July 2013}}. Similar preamp changes were also incorporated in the 5F8 Twin Amp at about the same time, but not on other large size Fender amps{{citation needed|date=July 2013}}.
During 1958, Fender introduced the model 5F6-A Bassman model. This final 1950s Tweed Bassman model product line included a change from the 5Y3 to the GZ34 rectifier tube, as well as a modification within the Presence control circuit. During early 1960, Fender began producing the 5F6-A Bassman with Jensen P10Q speakers. The P10Q Jensen speakers are more able to manage stronger electrical input power and generate better "clean" output sounds than previous installed P10R Jensen speakers. The P10R Jensen speakers were shipped within all Fender Bassmans from late 1954 until early 1960. Many professional music industry analysts have heralded the 1950s Fender 4x10 Bassman amps as the greatest guitar amp ever{{citation needed|date=July 2013}}. The first 1954 Fender Tweed 5D6 4x10 circuit generated further Tweed Bassman amplifier development through 1960. Several Bassman models were progressively influenced by the 5D6 through the last Fender Tweed 5F6-A Bassman's circuit design. The 5F6-A Bassman's design was directly copied by Marshall Amplifiers within their JTM-45 amplifier during the early 1960s.
This Fender, Tweed Bassman 5F6-A, 1959 is in perfect working condition and was used and owned by Mick Grabham (Procul Harum).He used it among others for the Procul Harum 1973 Hollywood Bowl concert, which was released as an LP.
