History of the JTM45

Rewind to the early 1960s - The Jim Marshall & Son store in Hanwell, London had just opened and was attracting many young emerging artists - who saw the store as a place to express their creativity and share ideas. These artists included John Entwistle and Ritchie Blackmore among others.

These same artists complained that amps available in the UK weren’t cutting it for the grit-driven rockers of the time, and the most popular amps were imported from overseas, often taking a long time to arrive. Jim and Terry Marshall saw this gap in the market and were inspired to build their own amplifier. Jim focused mainly on the cabinets of the product, while Terry, and then service engineer Ken Bran, looked at an RCA circuit and started experimenting with different components. Like Jim, neither Terry nor Ken were guitarists, and it was these different ears that enabled the Marshall Sound to be born. Along came the amp that started it all, ‘Number One’, the Jim Terry Marshall 45, more commonly known as the JTM®45.

So what happened?

The original amp was based on the Fender Bassman, the favourite amp of Terry Marshall at the time. Like the Bassman, early versions of the JTM used 6L6 or US 5881 valves in the output stage and later models were upgraded to the KT66, EL34, or KT88 valves. It wasn’t just the valves that the Marshall team changed over time, there were other significant changes made including the all-aluminium chassis, a 12AX7 valve as the first in the chain, and a modified negative feedback circuit which affected the harmonics produced by the amplifier.

As a result of these changes, the JTM had a large amount of feedback running through it. This not only meant that the harmonic content of the JTM was different to everything else that was around at the time, but also created the distorted and gritty sound that catapulted Marshall into fame.

After the prototype had been created and sold, demand soared for the newly developed amp, and orders soon came flooding in. It became clear that the added distortion was exactly what players were after. The original 'Number One' is now proudly on display at the Marshall factory in Bletchley.

After the prototype

Due to the size of the Marshall shop at the time, it was impossible to build these amplifiers in-house, instead, they were built in the sheds of the Marshall team.

In the very early days, it was possible for each JTM to sound different from the next. People would come into Jim’s shop and request slight alterations to their amp – a little more bass here, less treble there, extra gain and so on. We have on record, 24 different variations of the JTM45 over the first eight years, but the true number could be much higher. The most unique part of the first few amps was the way their electronics were laid out, with most of it being placed into one end of the amp; These amps were known as the Offset JTM45s. However, it soon became apparent that placing the electronics this way made them unbalanced and difficult to carry. This way of placing the electronics in one end was quickly stopped, with only a limited number ever being put into circulation.

Moving forward

The Marshall name was now known for distortion and loudness. But was it loud enough?

Well, it’s never loud enough! Design changes, like the use of a sealed cab, enabled 20w, and soon after 25w, versions to be created – a healthy boost up from the original 15W. It wasn’t just the interior that was updated, there were cosmetic changes too. Over the next three years, the exterior went from the original smooth black leatherette with blonde, to front metal plates with a red enamel font. Jim bought the metal plates from a funeral hardware store, earning them their affectionate name of ‘coffin badges’. It has been estimated that 200 of these badges were bought and less than 50 made their way onto customer-facing models. Other sources say that due to the high cost of each plate, every single one was used and sold. The amp cabinets also became longer, and the thick look of the front edges was removed. At the end of 1963, we finally get to see the all-black livery that is still the choice of design on our amps today.

In 1965, we advertised our first-ever combo amp, the 1962 model JTM45 MKIV ‘Bass and Lead’. Based on the JTM bass chassis with tremolo, the Series 1 2x12 combos were boxy and featured traditional JTM45 styling. These combos were open-back, made from Baltic birch, and had a gold block logo and white speaker fret cloth, paired with Celestion Alnico 15-watt T652 speakers. These were also available in a 4x10 format, known as the 1961 model. While it’s difficult to pinpoint transition periods, new cosmetic changes were introduced which included the instantly recognisable Marshall script logo, and grey and white pinstripe grille cloth. Alongside this, the Alnico speakers were switched out for G12M Greenback speakers. This combo amp eventually evolved into what is now known as the Bluesbreaker, thanks to the ‘Blues Breakers’ otherwise known as the ‘Beano’ album by John Mayall with Eric Clapton.

History of

JTM45

So what happened?

After the prototype

Moving forward

In the present day

Want to know more?

You might also like...