Marshall JTM45: every version
Every version, how to tell them apart, how to date one, and what to check before you buy. 6 versions, 1962–present.
The JTM45 was Marshall's first amplifier: a Bassman-derived head with two channels, a GZ34 valve rectifier and, from about 1964, KT66 output valves. It was built from the end of 1962 until 1966, when it became the EL34-powered JTM50. The same circuit went into the 1961 and 1962 “Bluesbreaker” combos and a 100-watt version, and Marshall has reissued the head and the 2×12 combo since 1989. The badge, the panel and the output valves date an original; the circuit board and the model number give away a reissue.
The versions, in order
JTM45 head (Late 1962–1966)
JTM
Marshall's first amp: two channels, four inputs, one shared tone stack, a GZ34 rectifier and, from about 1964, two KT66s.
How to spot one
- The earliest heads have white fabric fronts and a red-on-silver block-capital “coffin” badge; later heads carry the script logo.
- Aluminium front panels printed “JTM 45” arrive around 1963; gold plexiglass panels follow from about 1965.
- Controls: Presence, Bass, Middle, Treble, Loudness 1 and Loudness 2, with four inputs across the two channels.
- A GZ34 valve rectifier and three ECC83s; the earliest amps used 5881 (6L6-type) output valves, with KT66s standard by about 1964.
- An all-aluminium chassis, usually with a closed-back Celestion-loaded 4×12 cabinet rather than the open-back Bassman layout it was derived from.
Specs
| Power tubes | 2 × KT66 |
|---|---|
| Rectifier | GZ34 tube |
| Phase inverter | Long-tail pair |
| Preamp tubes | 3 × ECC83 |
JTM45/100 (1965–1966)
JTM
Marshall's first 100-watt head: four KT66s, and on the first examples two JTM45 output transformers.
What changed from the JTM45 head
- Power tubes: 2 × KT66 → 4 × KT66
- Two more KT66s for 100 watts; the first examples used two output transformers to carry the extra power.
How to spot one
- Four KT66 output valves instead of two.
- The first examples used two 50-watt output transformers side by side to handle the extra power.
- The same four-input, two-channel layout as the JTM45 head.
- It was soon succeeded by the 100-watt Super 100, the ancestor of the 1959 Super Lead.
Specs
| Power tubes | 4 × KT66 |
|---|
Model 1961 and 1962 “Bluesbreaker” combos (c. 1964–1972)
JTM
The JTM45 circuit with tremolo in open-back combos: the 1961 with four 10-inch speakers, the 1962 with two 12s.
What changed from the JTM45 head
- The head circuit went into open-back combos (4×10 and 2×12) with a tremolo circuit.
How to spot one
- Model 1961: a 4×10 combo; Model 1962: a 2×12 combo. Both have open-back cabinets and Celestion speakers.
- A tremolo circuit is part of the design.
- JTM45-era examples run two KT66s and a GZ34 for about 35 watts.
- Combos built after the move to the JTM50 (from 1966) use EL34s.
- Later production uses a slightly thinner cabinet than the earliest combos.
Specs
| Rectifier | GZ34 tube |
|---|
JTM45 2245 reissue and the Offset edition (1989 on)
Reissue
The JTM45 head reissued as the Model 2245: the original layout on a printed circuit board, still with a GZ34.
What changed from the JTM45 head
- Power tubes: 2 × KT66 → 2 × 6L6
- The reissue moved the circuit onto a printed circuit board and first shipped with 6L6-type output valves.
How to spot one
- Model number 2245 on the back panel.
- Printed circuit board construction, where the originals were hand-wired.
- Two channels and four inputs as on the original, with a GZ34 valve rectifier, rated at about 30 watts.
- The first reissues used 6L6-type output valves rather than KT66s.
- The limited Offset edition recreates the earliest coffin-badge heads; a hand-wired 2245THW with tremolo followed in 2014.
Specs
| Power tubes | 2 × 5881 |
|---|---|
| Rectifier | GZ34 tube |
| Phase inverter | Long-tail pair |
1962 Bluesbreaker reissue (1989 on)
Reissue
The 2×12 Bluesbreaker combo reissued with tremolo and a GZ34; 6L6s at first, 5881s from 1993.
What changed from the Model 1961 and 1962 “Bluesbreaker” combos
- Only the 2×12 Model 1962 was reissued; it kept tremolo and the GZ34 but used 6L6s, then 5881s from 1993, instead of KT66s.
How to spot one
- A 2×12 combo with the JTM45 circuit, tremolo and a GZ34 valve rectifier; the 4×10 Model 1961 was never reissued.
- Three ECC83 preamp valves.
- 1989 reissues use 6L6 output valves; from 1993 Marshall fitted 5881s.
- The 1989 reissue's tremolo has no footswitch.
Specs
| Rectifier | GZ34 tube |
|---|---|
| Phase inverter | Long-tail pair |
| Preamp tubes | 3 × ECC83 |
Super 100JH (2006 (limited edition))
Limited edition
A hand-wired, 600-piece recreation of a 1966 Super 100, the successor to the JTM45/100.
What changed from the JTM45/100
- A hand-wired recreation of the 1966 Super 100 that followed the JTM45/100, sold only as a limited stack.
How to spot one
- A limited run of 600, sold as a full stack with matching 1982A and 1982B cabinets.
- Four KT66 output valves and three ECC83s for 100 watts.
- Controls: Presence, Bass, Middle, Treble, Loudness 1 and Loudness 2.
- Hand-wired, recreating a 1966 head.
Specs
| Power tubes | 4 × KT66 |
|---|---|
| Preamp tubes | 3 × ECC83 |
| Construction | Hand-wired |
JTM45 buying checklist
Date it
- Badge and panel date an original: coffin badge and white fabric front on the earliest heads, aluminium “JTM 45” panels from about 1963, gold plexiglass panels from about 1965.
- Output valves help too: 5881s point to the earliest amps, KT66s to about 1964–66, and EL34s to the JTM50 that replaced the JTM45 in 1966.
- Early Marshalls have no consistent serial-number system, so the panel, components and transformer date codes are the better guide.
- A Model 2245 or a printed circuit board means a 1989-on reissue.
Check it’s original
- Check the output valves and their sockets: a JTM45 converted to EL34s, or a JTM50 fitted with KT66s, changes what the amp is.
- Original transformers carry their maker's markings and date codes that should fit the mid-1960s; replaced transformers are common.
- A GZ34 is expected on every JTM45; a solid-state rectifier points to a later JTM50 or a modification.
- Coffin badges and early panels have been reproduced, so look at the chassis, components and wiring, not just the front.
What usually needs work
- Filter capacitors on a 1960s head are long past their service life and should be checked before the amp is played hard.
- The GZ34 rectifier and KT66 output valves are the usual wear items; modern KT66s vary a lot in quality and fit.
- A JTM45 or 1962 reissue with 6L6-type valves needs its bias checked when changing valve types.
Questions buyers ask
Is the JTM45 a copy of the Fender Bassman?
Its circuit was derived from the 5F6-A Bassman, but British parts, KT66 valves and closed-back Celestion cabinets gave it its own sound.
What's the difference between a JTM45 and a JTM50?
From 1966 the head was renamed JTM50 and moved to EL34 output valves, and the GZ34 later gave way to a solid-state rectifier.
Is the Bluesbreaker a different circuit?
No. The 1961 and 1962 combos use the JTM45 circuit with tremolo added, in open-back cabinets.
Are the reissues hand-wired?
The 1989 2245 head and the 1962 combo reissue are built on circuit boards. The 2245THW (2014) and the Super 100JH are hand-wired.
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