Marshall Arts: Common Misunderstandings and Misconceptions of Marshall Amps

By Mitch Colby

Last issue I discussed a few general amp terms that are commonly misused by guitarists, collectors and even a few experts. This time I’m going to be more specific and focus on misconceptions and misunderstood terms related to Marshall amps. Since I was associated with Marshall for 30 years, I am very aware of a lot of the confusion surrounding Marshall product names and terminology as well as commonly misconstrued facts about the products. Below I’ve discussed a few of the most common terms about Marshall amps that many guitarists don’t fully understand and concepts that are frequently misinterpreted in articles and discussions.


Several different series of very early Marshall models were identified with the “JTM” prefix, such as JTM45, JTM50 and JTM45/100. JTM stands for Jim and Terry Marshall. Many think that Terry was Jim Marshall’s wife, but that’s not the case, as Terry is Jim’s son. Terry worked for the Marshall company on and off for years. Most notably he was involved in artist relations in the company’s very early years. Marshall used other three-letter acronyms mostly for different series of amps (not individual model numbers), such as JCM, which are the initials for Jim’s full name—James Charles Marshall, and JVM, which stands for Jim and Victoria Marshall. Victoria is Jim’s daughter who also worked for the company.

The JTM45 is a 45-watt amp

Although the Marshall JTM45 can put out about 45 watts when driven into full distortion, it typically puts out about 30 to 35 watts of clean power and really should be considered a 30-watt amp. This flexibility in power rating is often the case with guitar amps. Some will put out more than the stated power rating and some less. For example, some early Marshall Super Lead amps with high plate voltages can put out 120 watts clean and over 150 watts at full bore, which is not so easy on the EL34 power tubes!


The term “Marshall Bluesbreaker” was coined by musicians as an unofficial name for the Marshall combo amp that Eric Clapton used on John Mayall’s Blues Breakers with Eric Clapton album. Clapton’s Marshall amp, which is pictured on the back of the album cover, is the 1965/66 version of the model 1962. The 1962 was a JTM45 amp with tremolo (model 2245) housed in a 2×12 combo featuring a pair of 20-watt Celestion Greenback speakers. Because the model 1962 amp has become highly collectable, many other Marshall combos are often called Bluesbreakers as well.

In my mind, the only true Bluesbreaker combos are those that have the same amp chassis (JTM45 with tremolo), including the first version (called Style 1), which had a slightly different cosmetic configuration, thicker wood sides, two Vox-style brass vents, and 15-watt alnico speakers. I’d also include Marshall’s 2×12 and 4×10 combos from 1964 through about 1966 in the Bluesbreaker category. The front of these amps had the split look with vinyl on the top valence and pinstripe grill cloth on the bottom. Later combos used the 50-watt chassis, which employed EL34s rather than KT66s. Most of these later amps also have basketweave grill cloth on the entire front of the amp. An even rarer version of the later combos had vinyl on the top and salt-and-pepper grill cloth on the bottom. While both of these 50-watt combos are fine amps and are actually preferred by some players because they sound more like a typical Marshall, they are not Bluesbreakers.

The biggest misapplication of the Bluesbreaker name is its use for the 10-, 18- and 20-watt combos of the Sixties and early Seventies. These combos, which came in all the cosmetic configurations described above as well as in 1×12, 2×10 and 2×12 versions, are often referred to as “mini Bluesbreakers.” While these are fine amps, especially the 18-watter, they aren’t Bluesbreakers.

Marshall also used Bluesbreaker as a model name for overdrive pedals. While these pedals may be the only truly official use of the Bluesbreaker name to appear on a Marshall product, they are not the Bluesbreaker amp that many guitarists speak of in reverent tones.

Model Numbers

Many of Marshall’s model numbers start with “19” such as 1959, 1987, 1962 and so on. These are model numbers only and do not represent a date. A Marshall amp with the model number 1959 is a 100-watt Super Lead head, which Marshall produced between 1966 until 1981. There is no possible way that 1959 could refer to the date that the amp was made as Marshall did not start making amps until 1962!


JCM800 is the name of a range of Marshall amplifiers from the Eighties, not a single amp model. The JCM800 series included both Master Volume (2203 and 2204) and Split-Channel Reverb (2210 and 2205) heads as well as a variety of combos. The Split-Channel Reverb amps far outsold the Master Volume amps, but the Master Volume models are usually the amps people refer to now when they say JCM800 because they were preferred by touring bands. Due to the popularity of the Master Volume JCM800 heads, Marshall offers a reissue of the amp.

Mitch Colby helped develop many Marshall and Vox amp designs and is the founder of Colby Amplification.

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