Fender Bassman: every version

Every version, how to tell them apart, how to date one, and what to check before you buy. 8 versions, 1952–present.

The Bassman was built as a bass amp and became one of the most copied guitar circuits ever: the 5F6-A tweed 4×10 is the amp the first Marshall, the JTM45, was based on. Over twenty years it went from a single 15-inch combo to a 4×10 tweed, then to piggyback heads in blonde, black and silver, each with different circuits. The tube chart stamp and the parts codes date it; the wiring, not the label, tells you which circuit it really is.

The versions, in order

Bassman 5A6 / 5B6 (1×15) (1952–1954)

Early tweed

The first Bassman: a tweed combo with one 15-inch speaker, octal tubes and just Volume and Tone.

How to spot one

Tweed combo with a single 15-inch Jensen speaker; introduced in 1952 in the “TV front” cabinet and changed to the wide-panel cabinet in 1953.
Split chassis: the control panel sits at the top of the cabinet and is joined by a cable to the main chassis mounted in the bottom.
Single channel with two inputs and just Volume and Tone controls.
Octal tubes: 6SC7 preamp, 6SL7 phase inverter, two 6L6-type output tubes and a 5U4 rectifier.
A sheet titled 'Bassman Amp 5A6' survives, but its circuit (two 6SJ7 inputs, 6N7 inverter, two speaker outputs) is the 1946–47 V-front Dual Professional; no Bassman built to it is known.

Specs

Power tubes	2 × 5881
Rectifier	5U4 tube
Phase inverter	Paraphase
Rated power	About 26 W
Speakers as shipped	1 × 15" Jensen

Bassman 5B6: amp page and presets

Bassman 5E6 / 5E6-A (1955–1957)

Narrow-panel tweed

The first 4×10 Bassman in our catalog: narrow-panel tweed, two channels, Presence, and two rectifier tubes.

What changed from the Bassman 5A6 / 5B6 (1×15)

One 15-inch speaker became four 10s in the narrow-panel cabinet.
Fixed bias replaced the earlier output-stage bias arrangement, giving more clean headroom.
Two rectifier tubes instead of one.
Nine-pin 12AY7 preamp tubes replaced the octal 6SC7/6SL7 types; two channels (Normal, Bright) and a Presence control were added.

How to spot one

Narrow-panel tweed combo with four 10-inch Jensen speakers.
Two 5U4GA rectifier tubes, where most Fender guitar amps of the time used one.
Two channels (Normal and Bright) with Presence, Bass, Treble and two Volume controls.
12AY7 preamp tubes and a fixed-bias output stage.

Specs

Rectifier	2 × 5U4GA tube
Speakers as shipped	4 × 10" Jensen

Bassman 5F6 (1957–1958)

Narrow-panel tweed

The short-lived first version of the classic circuit: Middle control, long-tail phase inverter and a single 83 mercury-vapor rectifier.

What changed from the Bassman 5E6 / 5E6-A

Rectifier: 5U4 tube → 83 tube
The cathodyne phase inverter was replaced by a long-tail pair.
A Middle control was added (three-knob tone stack), with two inputs per channel.
The two 5U4GA rectifiers were replaced by a single 83 mercury-vapor rectifier.

How to spot one

A single 83 mercury-vapor rectifier tube instead of the two 5U4GAs.
Adds a Middle control (Treble, Middle, Bass) and two inputs per channel.
Long-tail-pair phase inverter.
Four 10-inch Jensen P10R speakers.

Specs

Power tubes	2 × 5881
Rectifier	83 tube (mercury vapor)
Phase inverter	Long-tail pair
Speakers as shipped	4 × 10" Jensen P10R

Bassman 5F6: amp page and presets

Bassman 5F6-A (1958–1960)

Narrow-panel tweed

The famous one: the 5F6 layout with a GZ34 rectifier. The circuit the Marshall JTM45 was based on.

What changed from the Bassman 5F6

Rectifier: 83 tube → GZ34 tube
The 83 rectifier was replaced by a GZ34.
The Presence control circuit was modified.

How to spot one

The same narrow-panel 4×10 tweed combo and six-knob layout as the 5F6, but with a GZ34 (5AR4) rectifier tube.
Tubes: a 12AY7 and two 12AX7s in the preamp and phase inverter, two 5881 output tubes, GZ34/5AR4 rectifier.
Shipped with Jensen P10R speakers; some late examples (around 1959–60) have Jensen P10Qs.
The leather handle was replaced by a rubber “dog bone” handle during 1959.
The original output transformer is Triad part 45249 (also used on the 5F6).

Specs

Power tubes	2 × 5881
Rectifier	GZ34 (5AR4) tube
Phase inverter	Long-tail pair
Preamp tubes	12AY7 + 2 × 12AX7
Speakers as shipped	4 × 10" Jensen P10R (some late P10Q)

Bassman 5F6-A: amp page and presets · schematic redraw (Pro) · Bassman 5F6-A vs Marshall JTM45 · Bassman 5F6-A vs Fender Deluxe 5E3

Bassman 6G6 / 6G6-A / 6G6-B (c. 1961–1964 (varies))

Brownface / blonde piggyback

The Bassman becomes a head and separate cabinet in blonde Tolex, with Presence kept and, from the 6G6-A, a solid-state rectifier.

What changed from the Bassman 5F6-A

The combo became a piggyback head and separate cabinet in blonde Tolex with a brown control panel.
The 6G6-A switched from a GZ34 tube rectifier to a solid-state rectifier.

How to spot one

Piggyback: separate head and speaker cabinet in blonde Tolex, with a brown control panel and white knobs.
The earliest (1961) examples have rough blonde Tolex and oxblood (maroon) grille cloth; later ones have smooth blonde Tolex and wheat grille cloth.
6G6: GZ34 tube rectifier and a single 12-inch speaker; the first cabinets used a “tone ring” 1×12 design with the speaker floating between two baffles.
6G6-A and 6G6-B: solid-state rectifier and a 2×12 cabinet.
Four 7025/12AX7 tubes, two 5881/6L6-type output tubes, about 50 W, Presence control retained.
A brief 1964 transition amp, the 6G6-C, also exists: often a black control panel but still with Presence, and its tube chart may read 6G6-B.

Specs

Power tubes	2 × 5881
Phase inverter	Long-tail pair
Rated power	About 50 W

Bassman AA864 / AA165 / AB165 (1964–1967)

Blackface piggyback

Black Tolex and black panel, Presence gone, a 12AT7 phase inverter, and from AB165 an extra gain stage and a bias-balance control.

What changed from the Bassman 6G6 / 6G6-A / 6G6-B

The Presence control was removed (AA864, August 1964).
The phase inverter changed from a 7025 to a lower-gain 12AT7.
AB165 added a gain stage shared by both channels and turned the adjustable bias into a bias-balance control.

How to spot one

Black Tolex, black control panel, silver grille cloth and numbered black skirted knobs; 2×12 cabinet.
No Presence control (removed with the AA864 in 1964).
The circuit code dates the drawing: the last two digits are the year and the digit(s) before them the month, so AA864 is August 1964 and AB165 January 1965.
AA864 has a true adjustable bias pot; AA165 and AB165 use a bias-balance pot that mainly shifts one tube against the other.
AB165 adds a gain stage shared by both channels, which makes it break up earlier than the AA864.
AA165 was a short-lived 1965 transition circuit between AA864 and AB165.

Specs

Power tubes	2 × 6L6GC
Rectifier	Solid-state (silicon diodes)
Phase inverter	Long-tail pair (12AT7)
Rated power	About 50 W

Bassman AC568 / AA270 / AA371 (Late 1960s into the 1970s)

Silverface piggyback

Silver panel, the AB165-style shared gain stage, and feedback networks that tame the breakup.

What changed from the Bassman AA864 / AA165 / AB165

The silver panel and blue/silver grille cloth replaced the blackface look; early silverface heads kept the AB165 circuit.
Later silverface circuits (AC568, AA270, AA371) kept the shared gain stage and used unusual feedback networks.

How to spot one

Silver control panel and blue-and-silver sparkle grille cloth; early heads have a thin aluminium “drip edge” trim around the grille cloth.
7025 preamp tubes and a 12AT7 phase inverter, with fixed bias.
AC568, AA270 and AA371 follow the AB165 layout, with a third gain stage shared by both channels and unusual feedback networks that tame breakup.
Early silverface heads kept the AB165 circuit.

Specs

Phase inverter	Long-tail pair (12AT7)

'59 Bassman reissue / '59 Bassman LTD (1990–present)

Reissue

A 5F6-A in layout and looks, built on a circuit board, with three 12AX7s and 6L6GCs.

What changed from the Bassman 5F6-A

Printed circuit board instead of hand wiring.
A solid-state rectifier on early reissues; the LTD returned to a 5AR4 tube.
Three 12AX7s in place of the original 12AY7 and two 12AX7s, and 6L6GC output tubes.
A standby switch and an internal bias pot.

How to spot one

Narrow-panel tweed 4×10 combo with the same six-knob layout (Presence, Middle, Bass, Treble, two Volumes) and four inputs.
Printed circuit board construction, unlike the hand-wired original.
Early reissues use a solid-state rectifier and four Eminence-made alnico “blue frame” 10-inch speakers.
The later LTD uses a 5AR4 rectifier tube, Jensen P10R reissue speakers and lacquered tweed; it's rated 45 W.
Has a standby switch and an internal bias adjustment pot.

Specs

Power tubes	2 × 6L6GC
Phase inverter	Long-tail pair
Preamp tubes	3 × 12AX7
Construction	Printed circuit board

'59 Bassman reissue: amp page and presets

Bassman buying checklist

Date it

From about 1953 through the 1960s Fender stamped a two-letter date code on the tube chart: first letter the year (C = 1953, D = 1954 … J = 1960, K = 1961 … Q = 1967), second letter the month (A = January … L = December). “HH” is August 1958.
Pots carry an EIA code: maker, then year and week. 137 is CTS and 304 Stackpole, so 137-6504 is a CTS pot from week 4 of 1965. A single year digit can be ambiguous (…5 could be 1955 or 1965), so read it with the amp's cosmetics.
Jensen speakers use maker code 220: 220 5 48 is a Jensen from week 48 of a year ending in 5.
Transformers use the same scheme; Schumacher is 606 (606-9-32 is week 32 of 1959). Tweed Bassmans also used Triad transformers.
Serial numbers aren't a reliable way to date these amps; use the tube-chart stamp and the parts codes.
Parts codes only show when a part was made, so the amp was assembled on or after the newest code.
On mid-1960s Bassmans the circuit code dates the drawing: AA864 is August 1964.
The circuit printed on the tube chart doesn't always match the wiring (AA864 charts in AA165 amps, 6G6-B charts in 6G6-C amps).

Check it’s original

Check the output transformer: the tweed 5F6/5F6-A original is Triad 45249, and reproductions exist, so confirm the date code as well as the part number.
Original speakers are often missing or reconed; a period-correct recone is service, not a fake, but it should be disclosed.
Replaced filter capacitors are normal maintenance on these amps, not a loss of originality.
Silverface heads are very often modified, commonly “blackfaced” toward the AA864 circuit; look for non-factory changes around the bias and feedback circuits.
Late blonde and blackface 2×12 cabinets shipped with a mix of 12-inch speakers (Jensen, Oxford, Utah), so different brands in one cabinet can be original.
A 1990s-on reissue is easy to tell from an original by its printed circuit board and three-12AX7 line-up.

What usually needs work

Electrolytic filter caps dry out: bulging, leaking or crusty caps, hum, crackles or “motorboating” mean they need replacing on any original-cap amp.
Leaking filter caps can damage the transformers, so a cap service protects the most important original parts.
All but the earliest Bassmans are fixed-bias, so check and set the bias whenever the output tubes are changed.
AB165-and-later heads only have a bias-balance pot, so setting the overall bias usually needs a resistor change or a modification.
Paper speaker cones dry out and tear with age; expect recones or replacements on 1950s–60s speakers.

Questions buyers ask

Is the '59 Bassman reissue the same as an original 5F6-A?

Same basic circuit and layout, but built on a printed circuit board, with three 12AX7s instead of a 12AY7 in the first slot and, on early reissues, a solid-state rectifier.

Is the Marshall JTM45 based on the Bassman?

Yes. The first Marshall, the JTM45, was based on the 5F6-A tweed Bassman circuit.

Which Bassmans have a tube rectifier?

The tweed Bassmans and the first 6G6 piggyback. From the 6G6-A on the rectifier is solid-state; the reissue LTD brought back a 5AR4 tube.

How do I date my Bassman?

Read the two-letter stamp on the tube chart (first letter the year, second the month), then confirm with the pot, speaker and transformer date codes. Don't rely on the serial number.

Does my blackface Bassman's tube chart tell me which circuit it has?

Not reliably. Labels were used up across circuit changes, so check the wiring against the AA864, AA165 and AB165 schematics.

Amp vs amp

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