History · Fender-style

The Bassman line

The Bassman began in 1952 as a companion for the new Precision Bass — a single-15" tweed combo meant to amplify a bass guitar cleanly. Over the 1950s it was reworked circuit by circuit until, in the 5F6-A of 1958, it had become one of the most admired guitar amplifiers ever built: four 10" speakers, a three-knob tone stack with presence, a long-tailed-pair phase inverter, and a loud, harmonically rich overdrive that guitarists — not bassists — prized. That tweed circuit became the template Jim Marshall's team copied for the first JTM45, seeding the British high-gain lineage. When Fender needed a real bass amp again in the 1960s, the name was moved onto an entirely different blackface piggyback head (AA864, then AB165), leaving the 4x10 tweed as a guitar classic in its own right.

1952–1967 8 models 1 documented 7 history-tier
Era timeline — each bar spans a model's production years; the chain from top to bottom is the line's succession.
1955 1960 1965 5B6 26 W 5D6 40 W 5E6 40 W 5F6 45 W 5F6-A 40 W ✓ 6G6 50 W AA864 50 W AB165 50 W
Documented circuit — links to its page History-tier — placed & sourced, circuit not yet drawn Succession within the line

The models

DesignationYearsWattsOutput stageKey changeCircuit
5B6 1952–1954 26 W push-pull 2x6L6 The origin of the line. Fender's first bass amplifier, designed to partner the 1951 Precision Bass: a cathode-biased tweed combo with a single 15" speaker and a two-control (volume, tone) front. The earliest TV-front examples used octal preamp tubes (6SC7 phase-splitter, 6SL7); the later wide-panel version switched to the nine-pin miniature tubes (12AY7/12AX7) that the rest of the line would keep. history entry
5D6 1954–1955 40 W push-pull 2x6L6 The two big structural moves happened here: the single 15" speaker gave way to four 10" speakers, and the power section changed to fixed bias (raising output) fed by a pair of rectifier tubes — the "dual rectifier" Bassman — with a cathodyne (split-load) phase inverter. Very short-lived and quickly superseded; sources disagree on exactly how long it ran, with the 5D6/5E6 transition variously dated across 1954-1955, so the range here is the defensible one. history entry
5E6 / 5E6-A 1955–1957 40 W push-pull 2x6L6 Evolutionary refinement of the 4x10 dual-rectifier circuit rather than a redesign, carried in the narrow-panel tweed cabinet. The 5E6-A tidied the preamp and tone circuit further. This is the mature dual-rectifier era that immediately precedes the milestone 5F6. history entry
5F6 1957–1958 45 W push-pull 2x5881 The circuit that made the amp famous. It replaced the earlier tone circuit with a three-knob stack — separate Treble, Middle and Bass — plus a Presence control, and swapped the cathodyne splitter for a long-tailed-pair phase inverter that gave more drive and headroom. The drawing shows a single 83 mercury-vapor rectifier feeding a pair of 5881 output tubes into the 4x10 cab. This layout (Bright/Normal channels, Presence/Middle/Bass/Treble) is the direct predecessor of the 5F6-A. history entry
5F6-A 1958–1960 40 W push-pull 2x5881 The definitive tweed Bassman and the corpus's fully documented reference circuit. It refined the 5F6 mainly in the power supply and presence circuit, adopting the GZ34 rectifier in place of the 83. Its combination of the 4x10 cab, cathode-follower tone stack, long-tailed-pair inverter and fixed-bias 5881 pair became a reference point for guitar tone — and the circuit Jim Marshall's team studied when building the first JTM45, making this the seed of the British high-gain lineage. 5F6-A circuit ↗
6G6 / 6G6-A / 6G6-B 1960–1963 50 W push-pull 2x5881/6L6GC A complete break from the tweed combo: the Bassman became a piggyback rig — a separate head atop its own speaker cabinet — in brown then blonde Tolex, rated around 50 watts. The 6G6 kept a GZ34 rectifier; the 6G6-A moved to a solid-state rectifier and a two-12" cabinet. This brown/blonde era is the bridge between the tweed 4x10 guitar classic and the blackface bass head that followed. history entry
AA864 1964–1965 50 W push-pull 2x6L6GC The first blackface Bassman: black Tolex, black control panel, a 50-watt head over a separate cabinet, and a redesigned two-channel (Bass and Normal) circuit built for bass duty again rather than the tweed guitar voicing. Solid-state rectification replaced the rectifier tube. This is a wholly different amplifier that inherited the name, not the tweed circuit. history entry
AB165 1965–1967 50 W push-pull 2x6L6GC The best-known blackface Bassman circuit, running from the mid-1960s into the early silverface period. The drawing shows Bass and Normal channels on 7025 (12AX7-family) preamp tubes, a 12AT7 long-tailed-pair phase inverter, a pair of 6L6GC output tubes and a solid-state rectifier, with the distinctive blend/feedback network on the Bass channel. It shares only the name with the tweed 4x10 amps. history entry

A circuit ↗ badge links a fully documented circuit — redrawn schematic, verified operating point, parts list. A history entry is placed and sourced here but its circuit isn't drawn yet; contributions are welcome.

Dating & notes

Tweed-era dating is fuzzy and sources disagree, especially across the 5D6/5E6/5E6-A transition (variously placed in 1954-1957); the ranges given are the defensible ones rather than hard boundaries. The tweed line (5B6 through 5F6-A) and the 1960s piggyback heads (6G6 brown/blonde, then blackface AA864/AB165) are essentially two different amplifiers that share the Bassman name: the former became a guitar classic and the template for Marshall's JTM45; the latter was Fender's return to a purpose-built bass head. Cross-family influence on the JTM45 is documented in this corpus (amps/5f6a lineage 'influenced: jtm45') and lives in the marshall-lead family file; it is noted here only as the well-attested succession point, not claimed as a Bassman model.

Sources

Every model above carries its own citations in the corpus data file. Browse the full source list for this line: history/families/bassman.yaml.

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