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* EDIT: Up-to-date information is available in Yek's Guide to the Fractal Audio Amplifier Models *
Brit JM45: based on Marshall JTM 45
The JTM 45 was Marshall’s first amplifier in the ‘60s. Its design was entirely copied from the Fender Bassman. It was a hit, and a vintage JTM 45 is worth a lot, listing #6 on Vintage Guitar’s list of most valuable amps. Some production models were named JTM 50.
Vintage Guitar:
It is a different kind of Marshall tone than the later Plexi amps. Wikipedia:
Eric Clapton played a JTM 45 combo known as the Blues Breaker on the famous ’66 Beano album by the John Mayall Bluesbreakers. More JTM 45 history and more about Eric Clapton's amps and guitars.
The JTM 45 was re-issued by Marshall, with 6L6 tubes:
The JTM 45 uses KT66 tubes and is 30 watts. It has four inputs, two per channel.
It provides two channels: Normal and High Treble, and two inputs per channel. Fractal Audio has models of the High Treble channel and of the jumpered inputs.
Jumpered channels: some players use patch cables to “jumper” the inputs (2nd input of channel 1 goes into 1st input of channel 2). This enables them to have the benefits of both channels at once. This is modeled in the “Jumpered” model of the JTM 45. This model has two Drive controls. Set them at the same position, or keep Normal Drive lower than Treble Drive.
The High Treble channel is bright. The amp is also heavy on bass. Like a Plexi’s Normal channel, it’s not unusual to turn down the Bass control all the way to prevent the tone getting flubby.
Apart from the Volume controls for both channels, the amp has Bass, Middle, Treble and Presence controls.
The JTM 45 doesn’t have a Master Volume, so keep the Master control in the model dimed. Without a Master Volume control, the JTM relies on power amp distortion. To achieve a nice warm overdriven blues or rock tone, you need to turn up the drive a lot, and crank the tone controls. This makes it a very loud amp in real life.
Cliff:
Unlike its cousin the Fender Bassman, the JTM 45 was designed to be used with a 4x12 cabinet with Celestion G12M (greenbacks) or G12H speakers.
Greenbacks have a sweet midrange and good bass reproduction. The rear of those speakers was green, and the nickname “greenbacks” was born. Another popular speaker in those days (and still): the G12H, a 30 watts Celestion speaker that compresses less than a greenback and has a flatter response (“Jimi Hendrix” speaker).
You check this page for the stock "greenbacks" cabs, suitable for the Marshall models. Personal favorites among the stock cabs are: 54 and 55 (Cab Pack 20), 58 and 59 (Cab Pack 8), 103 (Cab Pack 2), 131 and 132 (Cab Pack 14, I think…).
Click to open the current re-issue’s handbook.
A selection of YouTube videos:
Brit JM45: based on Marshall JTM 45
The JTM 45 was Marshall’s first amplifier in the ‘60s. Its design was entirely copied from the Fender Bassman. It was a hit, and a vintage JTM 45 is worth a lot, listing #6 on Vintage Guitar’s list of most valuable amps. Some production models were named JTM 50.
Vintage Guitar:
“Despite being derived virtually point-by-point from Fender’s 5F6-A Bassman schematic, British components give the JTM45 a tone all its own.”
It is a different kind of Marshall tone than the later Plexi amps. Wikipedia:
“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.”
Eric Clapton played a JTM 45 combo known as the Blues Breaker on the famous ’66 Beano album by the John Mayall Bluesbreakers. More JTM 45 history and more about Eric Clapton's amps and guitars.
The JTM 45 was re-issued by Marshall, with 6L6 tubes:
“The very first Marshall amp, made back in 1962, was the JTM45. It was an instant hit and launched a whole new generation of groundbreaking guitar players and sounds. Since then, connoisseurs of tone have sought out rare original JTM45s from the ’60s. Now they shall seek no more, thanks to this meticulously accurate re-issue. It was GZ34 rectification that was the key to the JTM45’s sound, and this is a feature painstakingly reproduced in this re-issue. The way the rectifier interacts with the other valves causes subtle harmonics to shift and smoulder beneath every note, producing the unmistakable, original, and much emulated Marshall sound.”
The JTM 45 uses KT66 tubes and is 30 watts. It has four inputs, two per channel.
It provides two channels: Normal and High Treble, and two inputs per channel. Fractal Audio has models of the High Treble channel and of the jumpered inputs.
Jumpered channels: some players use patch cables to “jumper” the inputs (2nd input of channel 1 goes into 1st input of channel 2). This enables them to have the benefits of both channels at once. This is modeled in the “Jumpered” model of the JTM 45. This model has two Drive controls. Set them at the same position, or keep Normal Drive lower than Treble Drive.
The High Treble channel is bright. The amp is also heavy on bass. Like a Plexi’s Normal channel, it’s not unusual to turn down the Bass control all the way to prevent the tone getting flubby.
Apart from the Volume controls for both channels, the amp has Bass, Middle, Treble and Presence controls.
The JTM 45 doesn’t have a Master Volume, so keep the Master control in the model dimed. Without a Master Volume control, the JTM relies on power amp distortion. To achieve a nice warm overdriven blues or rock tone, you need to turn up the drive a lot, and crank the tone controls. This makes it a very loud amp in real life.
Cliff:
"They had no Master Volumes so people rarely got the Drive past 3.00 since it would melt your face. Without the specter of having your skin flayed off as is afforded by a model of the amp, the temptation is to turn the Drive way up. When you do this, the low notes get very muddy. Single notes can form an almost perfect square wave which will sound like a synthesizer.”
"Our model is based on Channel 2 which is the bright channel. Also our reference amp has a 100 pF bright cap. Many JTM45s did not but I think they sound better with one. A JTM45 with a bright cap is similar to a Superlead. If you want the Channel 1 sound with an Axe-Fx use the Brit JM45 Jump model and turn the Treble Drive knob all the way down."
"Our model is based on Channel 2 which is the bright channel. Also our reference amp has a 100 pF bright cap. Many JTM45s did not but I think they sound better with one. A JTM45 with a bright cap is similar to a Superlead. If you want the Channel 1 sound with an Axe-Fx use the Brit JM45 Jump model and turn the Treble Drive knob all the way down."
Unlike its cousin the Fender Bassman, the JTM 45 was designed to be used with a 4x12 cabinet with Celestion G12M (greenbacks) or G12H speakers.
Greenbacks have a sweet midrange and good bass reproduction. The rear of those speakers was green, and the nickname “greenbacks” was born. Another popular speaker in those days (and still): the G12H, a 30 watts Celestion speaker that compresses less than a greenback and has a flatter response (“Jimi Hendrix” speaker).
You check this page for the stock "greenbacks" cabs, suitable for the Marshall models. Personal favorites among the stock cabs are: 54 and 55 (Cab Pack 20), 58 and 59 (Cab Pack 8), 103 (Cab Pack 2), 131 and 132 (Cab Pack 14, I think…).
Click to open the current re-issue’s handbook.
A selection of YouTube videos:
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