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 9 models 6 documented 4 verified 3 history-tier

Era timeline — each bar spans a model's production years; the chain from top to bottom is the line's succession.

Verified circuit — operating point checked against a published chart Draft circuit — drawn and sourced, verification not complete History entry — placed & sourced, circuit not drawn yet Succession within the line

The models

Designation	Years	Watts	Output stage	Key change	Circuit
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. Sources for 5B6 (1) Wikipedia, 'Fender Bassman' — 5B6 origins: 1952 TV-front single-15 combo for the Precision Bass; octal 6SC7/6SL7/6L6/5U4 tube set; 1953-54 wide-panel revision adopting 12AY7/12AX7 — en.wikipedia.org	history entry Open requests for 5B6 ↗ Suggest research for 5B6 ↗
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 Very short-lived and quickly superseded; sources disagree on exactly how long it ran, with the 5D6/5E6 transition variously dated across 1954-1955, so the range here is the defensible one. Sources for 5D6 (1) Wikipedia, 'Fender Bassman' — 5D6 'Dual Rectifier Bassman': move to four 10-inch Jensen P10R speakers, fixed bias for more power, two rectifier tubes, cathodyne phase inverter, 12AX7 preamps — en.wikipedia.org	history entry Open requests for 5D6 ↗ Suggest research for 5D6 ↗
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: two 5U4GA rectifier tubes in parallel ahead of a choke, a 12AY7 two-channel front end, a second 12AY7 split into a gain stage and a cathode follower that feeds a Bass/Treble network, and a 12AX7 driver ahead of a split-load (cathodyne) phase inverter feeding the fixed-bias 6L6 pair, with the Presence control on the driver's cathode — one revision short of the 5F6, which replaces the cathodyne with a long-tailed pair and adds the three-knob tone stack. The 5E6-A's only documented change from the plain 5E6 is a bias-supply resistor swap (recorded as a handwritten correction on the 5E6 drawing) that deepens the 6L6 bias to run the plates cooler; the 5E6-A's own page tells that story. The tube complement and rectifier count above were corrected from the placeholder (12AY7, 12AX7, 12AX7; no rectifier) once that entry read them off the drawing. This row carries the combined 5E6 / 5E6-A designation, so it spans both revisions (1955-1957). The documented circuit is the -A specifically, whose own entry takes the later part of that range as the defensible window for the revision it draws. Sources for 5E6 / 5E6-A (3) El34World schematic archive, Fender Bassman 5E6 drawing (designation-indexed; the drawing prints model + values) — el34world.com El34World schematic archive, Fender Bassman 5E6-A drawing — el34world.com Wikipedia, 'Fender Bassman' — 5E6/5E6-A dated 1955-1957 as evolutionary improvements over the 5D6 — en.wikipedia.org	5E6-A draft ↗
5F6	1957–1958	40 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. Sources for 5F6 (3) Circuit Codex amp 5f6 (every value and the printed voltage chart read from the F-EG factory drawing; 83 mercury-vapour rectifier, 82k/100k long-tailed-pair PI, -48 V fixed bias, presence control in the tone-stack ground leg) — el34world.com Neither the 5F6 nor the 5F6-A drawing prints a power rating; the 40 W figure is carried across from the 5F6-A because the two circuits share the power transformer (8087), choke (14684), output transformer (45249), 5881 pair, printed rails and printed bias voltage — el34world.com Wikipedia, 'Fender Bassman' — 5F6 (July 1957): three-knob treble/middle/bass tone stack, long-tailed-pair phase inverter, single-rectifier design, four 10-inch P10R speakers — en.wikipedia.org	5F6 circuit ↗
5F6-A	1958–1960	40 W	push-pull 2x5881	The definitive tweed Bassman, and one of the six circuits in this line documented in full. 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. Sources for 5F6-A (2) Circuit Codex amp 5f6a (fully documented: every value and the printed voltage chart read from the I-EG factory drawing; GZ34 rectifier, 82k/100k long-tailed-pair PI, -48 V fixed bias) — el34world.com Wikipedia, 'Fender Bassman' — 5F6-A (1958-1960): GZ34 rectifier, presence-circuit modification; widely cited as one of the greatest guitar amps — en.wikipedia.org	5F6-A circuit ↗
6G6 / 6G6-A	1960–1962	50 W	push-pull 2x5881	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 (late 1960) kept a GZ34 rectifier; the 6G6-A (early 1961) 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. Sources for 6G6 / 6G6-A (2) El34World schematic archive, Fender Bassman 6G6-A drawing (designation-indexed piggyback circuit) — el34world.com Wikipedia, 'Fender Bassman' — 6G6 (late 1960) 50 W blonde/brown piggyback, GZ34 rectifier, 6G6-A (early 1961) solid-state rectifier and 2x12 cab — en.wikipedia.org	history entry Open requests for 6G6 / 6G6-A ↗ Suggest research for 6G6 / 6G6-A ↗
6G6-B	1963–1964	50 W	push-pull 2x5881	The last and most fully worked-out revision of the piggyback Bassman before the blackface changeover: still blonde Tolex, but now a genuine two-channel amplifier — Bass and Normal each carry their own two-stage preamp and their own Bass/Treble/Volume network, mixing only at a shared driver stage ahead of the long-tailed-pair phase inverter. It carries the 6G6-A's solid-state rectifier forward (no rectifier tube at all in this drawing) and drops the GZ34 the combined 6G6/6G6-A designation above still lists. Discontinued in 1964 when the blackface AA864 piggyback head took the Bassman name back to a purpose-built bass circuit. Sources for 6G6-B (2) Circuit Codex amp 6g6b (fully documented: every rail, every cathode value, and both phase-inverter plate voltages read from the printed chart on the E-FB factory drawing; solid-state full-wave rectifier off a centre-tapped HT winding, 82k/100k long-tailed-pair PI, -54 V fixed bias) — el34world.com Wikipedia, 'Fender Bassman' — 6G6-B circuit changes carried through 1963; the blonde/piggyback Bassman line ran 1960-1964, superseded by the blackface AA864 piggyback head in 1964 — en.wikipedia.org	6G6-B draft ↗
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 — two strings of three series silicon diodes, a standby switch and a choke. The two channels are not the same amplifier: Normal is the ordinary blackface pair of gain stages either side of a two-knob ladder, while the Bass channel adds a third stage behind a 2:1 divider and swaps the ladder for a two-rung version with a 50k treble pot under a 250k series resistor, a 10k bass pot, and a Deep switch that parallels a second 0.1 uF into the foot. This is a wholly different amplifier that inherited the name, not the tweed circuit. Sources for AA864 (2) Circuit Codex amp aa864-bassman (every value and the printed voltage chart read from the H-FD factory drawing, title block 'FENDER MODEL "BASSMAN-AMP AA864" P/B'; three 7025 preamps, 12AT7 long-tailed-pair PI with 82k/100k plates and a 22k tail returned through the 100 ohm feedback foot, -44 V fixed bias, solid-state rectifier, TR1 125P7D / TR2 125C1A choke / TR3 125A13A output) — el34world.com Wikipedia, 'Fender Bassman' — AA864 blackface circuit, 1964, black Tolex and control panel — en.wikipedia.org	AA864 (Bassman-style) circuit ↗
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. Sources for AB165 (2) Circuit Codex amp ab165 (every value and the printed voltage chart read from the D-FE factory drawing; three 7025 preamps, 12AT7 long-tailed pair with a 220k local feedback resistor from each output plate, 6L6GC pair fixed-biased at -45 V, solid-state rectification, rails +425/+415/+390/+320) — el34world.com Wikipedia, 'Fender Bassman' — AB165 introduced c. 1965, carried into the early silverface (drip-edge) period, trend toward cleaner sound and more headroom — en.wikipedia.org	AB165 circuit ↗

The circuit column says how far this model has been documented, in three states. A circuit ↗ badge links a verified circuit: redrawn schematic, parts list, and a simulated operating point held against the published voltage chart under a maintainer's sign-off. A draft ↗ badge links a circuit that is drawn, sourced and published, but has not completed that chain — its own page states what is unresolved. A history entry is placed, dated and sourced here, but its circuit isn't drawn at all yet.

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. The 5F6-A's influence on the JTM45 is recorded on both circuits' pages and told in full on the Marshall lead line's page; it is noted here only as the well-attested succession point, not claimed as a Bassman model.

Sources

Each model's own citations are listed in its row above, under “Sources for …”. The complete data behind this line — every model's fields as stored, including those the page doesn't print — is in history/families/bassman.yaml.

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