Classic Gear: The 1979 Marshall JMP502204 Master Model

Marshall’s plexi models of 1967-’69 are the stuff of many guitarist’s dreams, but cast your “mind’s ear” to the classic sound of rock guitar throughout the late ’70s, ’80s, and ’90s, and in many cases the amp you’re conjuring up will be a JMP50 2204 Master Model, much like this one.
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Marshall’s plexi models of 1967-’69 are the stuff of many guitarist’s dreams, but cast your “mind’s ear” to the classic sound of rock guitar throughout the late ’70s, ’80s, and ’90s, and in many cases the amp you’re conjuring up will be a JMP50 2204 Master Model, much like this one. After Randall Smith’s Mesa/Boogie amps with their scorching cascading-gain preamps began delivering super-sustaining lead tones at manageable volumes to just about every notable artist in the early to mid ’70s, the major names knew they needed to catch up to the high-gain game. Marshall’s response was to adopt a few of the Boogie’s tricks, but to keep the resultant sound entirely British. The amps they delivered became instant “latter-day classics,” and still remain a more accessible vintage option for players who can’t stretch to the hallowed JTM45s and plexis of the ’60s. And in truth, for many of us, these might be a faster track to the ripping Marshall tone we’ve been chasing all along.

Amp and photo courtesy of Mike Tamposi and Mark Bishop

In 1975 Marshall introduced its Master Models, which had factory-installed Master Volume controls to enable preamp overdrive without having to run the output stage at full whack, and producing the blistering volume levels that some playing situations just couldn’t hack any more. As such, the Model 2203 100-watter and Model 2204 50-watter had a second volume control placed between the end of the cathode-follower tone stack and the input to the phase inverter, but each was initially a little different in another essential way. Both amps had two inputs instead of the previous four on traditional non-master Marshall lead amps: On the first rendition of the 50-watt 2204 JMP Master Model of around 1975-’76, the High and Low inputs each used half of the first ECC83 preamp tube, with a different voicing for each via different cathode bias networks and different coupling caps on the way to the shared Volume control. In that sense, they weren’t all that much different from the four-holers that had come before, and which Marshall still made, other than in their inclusion of the Master Volume control itself.

The 100-watt 2203 JMP Master Model, on the other hand, had High and Low inputs that yielded entirely different results. Plug into the Low, and you would essentially tap the classic circuit, which ran as follows: first gain stage into tone stage into phase inverter. The High input, however, routed the signal through an extra gain stage before joining the rest of the Low input’s path, resulting in a hot signal that would have been virtually unmanageable without that Master Volume control. At this point, Marshall really was taking a page out of Mesa/Boogie’s book, and the cascading gain gave the amp much greater lead capabilities than, say, the Twin Reverb of the day, to which Fender had added a Master Volume in 1972, but not a cascading-gain stage.

Part way through 1977, the 50-watt Master Model amps were also given this hotter cascading preamp circuit. That further evolution means that amps like the pristine 1979 version featured in this issue are considered by many to be the best-sounding 50-watt Master Models of the era, and are generally preferred to the earlier renditions. Although the Master Models were notable as a new development, Marshall continued to produce non-master-volume amps at this time, too. The 50-watt Model 1987 Lead and 100-watt Model 1959 Super Lead largely retained the circuits of their legendary predecessors. Those, however, still had to be cranked up to foundation-rumbling levels to achieve singing lead tones just like in the old days, so most players who sought that sound gravitated toward the Master Models. Note that for ease of servicing, the US-import amps of the era were equipped with 6550 output tubes rather than the classic EL34s that were retained by amps staying in Britain and headed to Canada and much of Europe. Many American players modify their export Master Models to use EL34s (as has been done with this one), but plenty will also tell you that these amps sound perfectly ferocious—and still 100-percent Marshall—with the 6550s in there.

ESSENTIAL INGREDIENTS

► Two EL34 output tubes generating around 50 watts RMS
► Fixed-biased output stage
► Three ECC83 (12AX7) preamp tubes
► Cascading gain stages via “High Sensitivity” input
► Master Volume control
► Solid-state rectification

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