Marshall JTM 45
Encyclopedia
The Marshall JTM 45 is the first guitar amplifier
made by Marshall
. First produced in 1962, it has been called a "seminal" amplifier, and is praised as the most desirable of all the company's amplifiers.
speakers. The amplifier itself was based on the Fender Bassman
. It uses KT66
tubes (though early versions had used US 5881, a version of the 6L6
), and 12AX7
tubes (known in Britain as ECC83) in the pre-amplification stage.
Significant differences between the Bassman and the JTM include the all-aluminum chassis (it is less susceptible to hum than a steel chassis), a 12AX7 valve as the first in the chain (the Bassman has a 12AY7), the Celestion speakers with a closed cabinet (compared to open-backed Jensen
speakers), and a modified feedback circuit which affects the harmonics produced by the amplifier. As Ken Bran later said, "The JTM also had different harmonic content, and this was due to the large amount of feedback I had given it." The amp was also available as a bass (which lacked a "bright" switch) and a PA
version.
By the mid 1960s, the JTM 45 had become so popular that it began to supplant the ubiquitous Vox amps, even their AC50, though it was just as powerful.
In late 1965, Marshall introduced its now standard script lettering, in white, and by early 1966 it began calling the amplifiers "JTM 50". Some 100 early models had red lettering; these are especially collectible. Other cosmetic changes included a gradual switch to different knobs. The JTM 45 became the basis for many subsequent Marshalls, most notably the Bluesbreaker
. It ceased being produced in 1966, but was reissued in 1989, though with a modern printed circuit board and 6L6
valves.
Guitar amplifier
A guitar amplifier is an electronic amplifier designed to make the signal of an electric or acoustic guitar louder so that it will produce sound through a loudspeaker...
made by Marshall
Marshall Amplification
Marshall Amplification is a British company, founded by drummer Jim Marshall, that designs and manufactures music amplifiers, brands personal headphones/earphones , and, after acquiring Natal Drums, drums and bongos. Marshall amplifiers, and specifically their guitar amplifiers, are among the most...
. First produced in 1962, it has been called a "seminal" amplifier, and is praised as the most desirable of all the company's amplifiers.
History
The JTM 45 was first built in 1962, handmade in an all-aluminum chassis, by Ken Bran and Dudley Craven. Because of its power, Marshall decided early on to build it as a head, with a separate 4x12" cabinet with CelestionCelestion
Celestion is a British maker of loudspeakers.-History:The work of what would become Celestion started in Hampton Wick in 1924. Celestion Radio Company and Celestion Limited were formed in 1927, and two years later the company moved across the Thames to Kingston. The company grew rapidly, but was...
speakers. The amplifier itself was based on the Fender Bassman
Fender Bassman
The Fender Bassman was a bass amplifier introduced by Fender in 1952. Although it was originally designed for bass guitars, it was frequently used for normal electric guitar in rock and roll, blues, and country bands.-History:...
. It uses KT66
KT66
The KT66 is a beam tetrode/kinkless tetrode vacuum tube for audio amplification.KT66 is the designator for a vacuum tube introduced by Marconi-Osram Valve Co. Ltd. of Britain in 1937....
tubes (though early versions had used US 5881, a version of the 6L6
6L6
6L6 is the designator for a vacuum tube introduced by Radio Corporation of America in July 1936. At the time Philips had already developed and patented power pentode designs, which were fast replacing power triodes due to their greater efficiency...
), and 12AX7
12AX7
12AX7 is a miniature dual triode vacuum tube with high voltage gain. It was developed around 1946 by RCA engineers in Harrison, New Jersey, under developmental number A-4522. It was released for public sale under the 12AX7 identifier on September 15, 1947. The 12AX7 was originally intended as...
tubes (known in Britain as ECC83) in the pre-amplification stage.
Significant differences between the Bassman and the JTM include the all-aluminum chassis (it is less susceptible to hum than a steel chassis), a 12AX7 valve as the first in the chain (the Bassman has a 12AY7), the Celestion speakers with a closed cabinet (compared to open-backed Jensen
Jensen Electronics
Jensen Is a consumer electronics brand with a history that dates back to 1915 with Peter Jensen's invention of the first loudspeaker. Over the years the Jensen family of brands has grown to include Jensen, Advent, Acoustic Research , Phase Linear and NHT Loudspeakers in the United States and...
speakers), and a modified feedback circuit which affects the harmonics produced by the amplifier. As Ken Bran later said, "The JTM also had different harmonic content, and this was due to the large amount of feedback I had given it." The amp was also available as a bass (which lacked a "bright" switch) and a PA
Public address
A public address system is an electronic amplification system with a mixer, amplifier and loudspeakers, used to reinforce a sound source, e.g., a person giving a speech, a DJ playing prerecorded music, and distributing the sound throughout a venue or building.Simple PA systems are often used in...
version.
By the mid 1960s, the JTM 45 had become so popular that it began to supplant the ubiquitous Vox amps, even their AC50, though it was just as powerful.
In late 1965, Marshall introduced its now standard script lettering, in white, and by early 1966 it began calling the amplifiers "JTM 50". Some 100 early models had red lettering; these are especially collectible. Other cosmetic changes included a gradual switch to different knobs. The JTM 45 became the basis for many subsequent Marshalls, most notably the Bluesbreaker
Marshall Bluesbreaker
The Marshall Bluesbreaker is the popular name given to the Models 1961 and 1962 guitar amplifiers made by Marshall from 1964/1965 to 1972. The Bluesbreaker, which derives its nickname from being used by Eric Clapton with John Mayall & The Bluesbreakers, is credited with delivering "the sound that...
. It ceased being produced in 1966, but was reissued in 1989, though with a modern printed circuit board and 6L6
6L6
6L6 is the designator for a vacuum tube introduced by Radio Corporation of America in July 1936. At the time Philips had already developed and patented power pentode designs, which were fast replacing power triodes due to their greater efficiency...
valves.
Name, numbering
The first JTM 45s did not have the standard Marshall number that later amps had; not until 1965 did the models that derived from the JTM 45 receive numbers.| Model number | Watts | Dates | Features | Notes |
|---|---|---|---|---|
| - | 45 | 1962-1964 | 2 channels, 4 inputs | Also available in bass and PA versions |
| 1963 | 50 | 1965-1966 | 4 channels, 8 inputs | PA version; "JTM50 MK III" |
| 1985 | 45 | 1965-1966 | 2 channels, 4 inputs | PA version of JTM50 MK II |
| 1986 | 45 | 1965-1966 | High treble and normal channels | Bass version of JTM50 MK II |
| 1987 | 45 | 1965-1966 | High treble and normal channels | Lead version of JTM50 MK II; also with tremolo Tremolo Tremolo, or tremolando, is a musical term that describes various trembling effects, falling roughly into two types. The first is a rapid reiteration... as Model T1987 |
| 1989 | 45 | 1965-1966 | For electronic organs | Also with tremolo as Model T1989 |
| JTM 45 | 45 | 1989 - | 2 channels, 4 inputs | Reissue of original JTM45 (1987) |
Sound
For all of its differences with the Bassman, the sound of the JTM 45 is still described as "like a tweed Fender"; it has more sag and less crunch than the later Marshalls, and is favored for blues and rock rather than for hard rock and metal. The JTM 45 does not deliver the famous Marshall "crunch" that became so sought after.Notable users
- Angus YoungAngus YoungAngus McKinnon Young is a Scottish-born Australian musician, and the lead guitarist, songwriter, and co-founder of the rock and roll band AC/DC. He was inducted into the Rock and Roll Hall of Fame along with other members of AC/DC in 2003 and is known for his energetic performances,...
(live, Young has a JTM 45 in an isolation box under the stage) - Gary MooreGary MooreRobert William Gary Moore , better known simply as Gary Moore, was a Northern Irish musician from Belfast, best recognised as a blues rock guitarist and singer....
(reissue)