The Marshall Shopper’s Guide Part 1: Marshall Plexi Era

One of the most common questions we get here is, “What kind of Marshall amp should I buy?” We get countless questions not only about what type to get, but also questions about specific vintage vs. newer models, higher powered vs. lower powered models, types of speakers and how do they all sound, etc.

Marshall PlexiBut back to the first question regarding what kind of Marshall to get… That isn’t such an easy question to answer because the various Marshalls over the years have been really each optimized for particular types of tones and guitar types and have changed both due to the tastes and demands of musicians as well as for cost or manufacturing reasons. We’ll cover that and cover in general what seems to work the best to maximize a particular Marshall. Some work well with high-output style humbucking pickups, others really come alive with PAF (i.e. stock Gibson) types. While certainly there is much opinion about what makes good tone – which can be an argument in and of itself –  there are certain facts and consistencies of setups to avoid. In addition, there are some notable models that the potential buyer should be made aware of that may not be as solid or good sounding as another particular amp from the same series. We’ll explain those models and reveal why…

It’s easy to understand the love/hate attitudes among guitarists regarding Marshall amplifiers. Models have of course changed much through the years and while the well-known rock recordings seem to always get all the great Marshall tones, it can sometimes feel somewhat elusive for the person who has saved their money and gone out to get their first Marshall and then perhaps felt some disappointment by not hearing or obtaining all the sounds they expected.

I know this all too well because I was once in this category. For years I wanted a certain tone and I think where I failed first is I tended to put too much emphasis on the amplifier head of choice with little regard to the cabinet/speakers, type of guitar and pickup, etc. Of course I didn’t know about which Marshall to get in the first place and there wasn’t an Internet resource at the time (much less an Internet) as well to help. In any event, when I did purchase my first Marshall in 1989 (a brand new 100 watt channel switching JCM 800 2210 100 watt head), while it sounded o.k. and I was happy with it at first, I became discouraged over time in part because the amp didn’t seem to cut well through the band mix and also because a good friend of mine was playing through an older, seemingly less-sophisticated model and was getting a tone that was blowing mine away. It took years to full understand and grasp why, but to make a long story short, this guitar player friend of mine had factored in all the appropriate ingredients to his sound. He knew and understood that the amplifier itself was only part of the equation. He had the right cabinets, guitars, and pickups installed to maximize the sound he was after. It also helped that he had a fantastic technique so never discount the benefits of practice!

So with that all said, the purpose of this article is to simply cover a range of various Marshalls made throughout the years, discuss some of the good as well as the bad of the most popular, or well-known models. This article is by no means made to cover oddities such as Marshall’s “Club and Country Combo”, “Capri” or others like it, and at the same time, there’s no point in discussing the first series of early badge logo Marshalls made in the early ’60s. Not only are these rare, but are collectible and therefore expensive. The intention of this guide is simply to provide some input and experience about what has seemed to work and not work for me over the years during a period of many purchases and playing experiences through various Marshalls. The thoughts that I share here should also be credited to fellow friends and musicians that I’ve known and worked with throughout the years. They were invaluable and it was great to learn and grow as a result of the common goal and quest for great tone! I hope that this article can answer most of the questions you may have about shopping for your Marshall. Enjoy!

JTM 45 series, including “Blues Breaker” combo

These are the first series of amps to cover and certainly also the most expensive out of the group here we’ll talk about. Being the most expensive and most collectable, I will make the assumption that the majority of readers won’t be shopping for a $3,000-$5,000+ Marshall head or a combo that can cost twice that amount or more so we’ll make this section relatively brief. Again, there also will be little point in discussing the differences in transition from badge logo to script logos and those types of details with this particular series. Just the basics!

The JTM 45 head was available in lead, bass, and p.a. form and the circuits themselves were very similar throughout. The sound of a JTM 45 overall is a diverse one, offering warm clean tones as well as some pretty fat grinding overdrive or bluesy dirt available when turned up. Its design was largely based on the Fender Bassman, one of the world’s great guitar amps (a bit of an irony!), but the JTM 45 had a bit more grit and top end brightness to the tone, thanks to use of more negative feedback (i.e. presence) within the circuit than the Bassman. That said, these are certainly the least bright of all Marshalls and are again known for their rounder, warmer sound. The JTM 45 also was most often equipped with KT66 tubes, unique for a Marshall since the Marshall rock sound is more commonly equated these days with the EL34 tube. The KT66 is a very high-quality tube with a bit more headroom than the EL34 and allowed this amp to deliver some nice bottom-end frequencies in the mix. This model also incorporated a tube rectifier that, when the amp was played hard, contributed to a somewhat sagging or softer response because of the way the rectifier had difficulty providing all the full power when played to the limit – well, this easily added a bit more of a compressed feeling to the guitars playing through the amp.

The most common trait with Marshalls from this era up until the late JCM 800s was the fact that they had such simple designs. Four inputs that could be linked and patched together for different tones (check out the tricks and tips for Super Lead article – same concepts apply), no preamp gain control, no reverb, but plenty of tone. The JTM 45 series are among Marshall’s best for warm, bluesy tones – a fact that has elevated their value to collectors and players alike.

The “Blues Breaker” was the combo version of the JTM 45 and available in a cabinet equipped either with alnico or ceramic Celestion speakers with some models including a tremelo effect. Made famous by Eric Clapton when playing with John Mayall for the BluesBreaker’s LP, these combos can be had for the price of a small import automobile. It’s for this reason that I’m not going to cover the particulars about these amps or what to look for in terms of originality, etc., though I’ll discuss these specific trends with the various amp series that follow.

One area I WILL cover is the birth of the reissues, both the JTM 45 head and 1962 BluesBreaker combo. Both in my opinion are fine amplifiers, though not 100% accurate to the original by any means, are still good values for the money. The JTM 45 reissue head is perhaps my favorite of the reissue series of vintage Marshalls, though it is equipped with different power tubes than originally used (using 6L6, a.k.a. 5881), it does have the tube rectifier and resulting warmth and sag from a nicely built circuit.

The Blues Breaker reissue combo also incorporates the same tube set as the JTM 45 and includes tremolo as well. Its cabinet has less depth than the original Blues Breakers and hence bottom end suffers just a hair.

For those looking to make the most of their JTM 45 reissue amplifier heads, ensuring that a good quality set of tubes that are properly biased will take these amps a long way. The tubes can be swapped for KT66s as well if so desired (some versions of the larger KT66s may not fit in the Blues Breaker combos). For those that want to really make an even closer approximation of a true JTM 45 or Blues Breaker (and this applies to ANY of the reissue series by the way), a big tonal difference can be had if the reissue model’s output transformer is changed over to a higher quality unit such as those made by Heyboer or Mercury Magnetics. These models of transformers are basically blue-printed sonically and physically from the originals. People don’t usually think about swapping output transformers, but especially when you play these amps hard, the tonal coloration of the transformer definitely comes into play. The output transformer is after all, the final link between the tubes and the speakers. In my opinion, today’s Marshall output transformers used in the reissues series overall are lacking, with my least favorite being the tone in the 100 watt 1959 SLP reissue. It is the transformer in part that causes the grainy, over trebly type of tone with additional transformer saturation/compression added to the mix. The original transformers used in the original JTM 45s and plexi amplifiers were by far superior. And the transformers manufactured by the specialty companies mentioned have done a fantastic job recreating them and are a great way to add tone to a struggling reissue amplifier.

But a final note now on the JTM 45 and Blues Breaker combo circuits… because of the extended bass frequency in the circuit, it is easy to obtain a flubby sound if too much bass is put through the circuit when turning the amps up, so take it easy with the bass control! I know a lot of guys who run the bass controls between 0 and 2 on these amps when they are driving the volume hard.

The Plexi Era of 100 and 50 watt Lead and Bass Heads

1969 JMP 100 Watt Super LeadMarshall wanted to up the power of its amplifiers because players of the time were demanding it. P.A. systems were rather inadequate so were often reserved for key areas such as vocals, overhead fill, etc. And while I’m not here to talk about the invention of the stack, I do want to talk in general about the various models in the plexi era and then provide some detail on what to look for when shopping for them, etc.

The earliest plexi 100s were actually those that had the same front panel as the JTM 45, and are known as the JTM 45/100 heads. What differentiates these between the later JMP plexi Marshalls is the fact that they employed very large transformers and the filter caps for the power supply were all placed underneath the chassis. All Marshalls during this era were hand-wired point to point with no printed circuit boards. The larger transformers and high plate voltages applied to the earliest 100 watt plexis meant that they had a lot more headroom, were very loud, and also wore down tubes fairly hard. JTM and MK II issue 100 watt lead and bass amplifiers can be thought of as basically louder versions of their smaller JTM 45 cousins. These amps were produced in ’66-’67 and are the most expensive of the range. Again, they were available in lead and bass versions that were somewhat similar, many of the smaller differences disappearing after the volume was cranked up.

In 1968, Marshalls plexi amps were labeled with a JMP logo on the front panel, and the sizes of both the output and power transformers and corresponding plate voltages were reduced somewhat, leading to a bit more reliable performance. The transition from filter cap placement from the bottom board chassis, to being top-mounted occurred gradually during this era as well. JMP plexi Marshalls are the most commonly available and are certainly the most affordable of the Marshall vintage plexi amp lineup.

Sonically, JMP versions of the plexi had a touch more gain, some of this in theory can be attributed to the tone of the output transformer and resulting saturation occurring when it was downsized a bit. There were other technical changes in the circuit from shared to split cathode (though I’m going to avoid this type of technical talk in this article). The bottom line is if we had to place these amps in a comparison between the earliest JTM 45 amps and the next series of metal-panel Marshalls, while the JTM 45s would be considered the bluesiest and the early metal panels, the most aggressive with loads of distortion, we could safely put JMP plexis somewhere in-between the two. This makes them very popular rock and blues amplifiers that happened to have also been very well built.

Now like the JTM 45, there were various versions of these plexi amplifiers. There were Bass (50 watt), Super Bass (100 watt), Lead (50 watt), and Super Lead (100 watt) heads in addition to a range of p.a. heads and later the 200 watt Marshall Major. There also consisted of Tremelo and Super Tremelo heads that of course added – you guessed it – a Tremelo effect that could be footswitched. The 200 watt Major is rather rare and a different circuit and tube set. I honestly don’t have any personal experience playing through one so won’t comment on them except to note that they are said to be a different type of Marshall sound. The P.A. and Super P.A. heads on the other hand, while unusual to find, are probably the most affordable in the bunch and are quite a good choice for those looking for an original plexi on a budget. Why are they cheaper you may ask? – Are they worse amps to have? On the contrary, p.a. heads just don’t hold the same allure as Super Lead amps for example. That said, with eight inputs, it’s very common to have these voiced where the first set of inputs are set to lead specifications and the second are set to bass.

Now let’s cover some fun questions:

What do the plexi series amps sound like?

In general terms, the earliest plexi amps from circa 1966 and 1967 were typically the loudest – though remember we’re talking in relative terms: they’re ALL loud! In addition, early MK II and JTM 45/100 series amps had the most amount of available headroom and also tended to distort just a bit less then the JMP-marked plexi amps that began its run in 1968. The earliest models also had slightly less brightness and crunch of the later plexi amps. In this regard, they are favored for their loud bluesy tones and warmth.

In 1968, the JMP-marked plexi amps arrived and had reduced plate voltages that were easier on the power tubes and a bit more brightness in the circuit to add some crunch. A stock Super Lead from this era will give a nice full-sounding crunch chord at high volumes and while these aren’t the most valuable from the plexi 100 and 50 lineup, they’re my personal favorite. A Super Bass from the same era will have just a hair less gain and in fact will sound closer to the MK II and JTM 45/100 amps that preceded it. Super Bass amps pack quite a wallop of power – or at least they feel that way because of how the circuit is tuned. In any case, the basic Super Lead and Super Bass circuit are both extremely similar and conversion to either type is very easy to do.

How can my plexi Marshall sound best – what types of guitars and cabinets should I use?

1971 4x12 CabinetReference the tone tips and tricks article on Marshall Super Leads as it applies in particular to these amps. Beyond that, from my personal experience, if playing a guitar equipped with a humbucking pickup, a PAF-style to medium gain pickup works best, rather than a high output or super-high output ceramic-based model. High output pickups have extended lows and highs that are not very clear often so the resulting mix through these era Marshalls is a muddied type of tone. Now there ARE some Marshalls that do tend to favor high output pickups when used for certain styles and we’ll get that to that later. But definitely not recommended for plexis – at least my personal ears don’t recommend them, but this can be an opinionated piece.

Regarding cabinets, since writing the tips and tricks for the Super Lead article, I’ve had a chance to aquire and play through two basketweave style cabinets. The combination of the basketweave material which dampens some of the brightness as well as the solid wood construction including the back (versus the particle board backs that started from late ’71 and onward), and original 25 watt Greenback speakers to me is the epitomy of the ultimate Marshall cabinet. Celestion Greenback speakers have a nice full sound with good bottom end and smooth mids and exhibit nice breakup in their sonic characteristics. G12H30s are also a good choice and have larger magnets and power handling capability. Ironically, the larger magnet does NOT seem to make it have a stronger or fatter bass response as one would tend to think. These are a cleaner speaker that still retains warmth. Not as much breakup as the Greenback, the G12H30 also doesn’t have a tendency to get mushy when pushed very hard as can occur with a Greenback G12M 25. Both excellent choices. Now as to reissue versus the originals? G12H30 anniversary reissues are said to be more accurate in construction and design to the originals and indeed sound good. Plenty of people also like the G12M 25 watt greenback reissue though it does exhibit quite a bit more brightness in its tone. Some of this may be due to aging since speakers will roll off some of their highs after years of use. In the end, my choice is my ’71 solid-back basketweave cabinet loaded with G12M 25s with original cones. Sounds great and better to my ears than any of my other cabinets, even when playing newer Marshalls!

What year is this old amp? How to identify the year of the Plexi

1968 JMP 50 Watt PlexiThis can be tricky and is easier for 50 watt models in particular because they had codes on the transformers that could reveal and indicate the year of manufacture. Here are some other general spotting clues. The first one isn’t a clue at all, but really a tell-tale sign. Look at the chassis of the amplifier as it may have its inspection tag still attached with a legible test date. If it’s there, no need to read further in this section! Otherwise, some general things to look for:

Circa 1965-early 1966: JTM 45 identified on front panel for 100 watt amps indicates first of the series. Switchover afterward to “MK II” label on front. Many models had no option to run U.S.A. power supply and require running a separate outboard transformer to convert European voltages to appropriate modern 120 V AC current. Filter capacitors all located on underside of chassis (filter capacitors are the circular blue or silver cans that look like tubes that are on the top side of most Marshall chassis standing vertical with the other tubes around them). 50 watt models all in small box head enclosures throughout the plexi era. 50 watt heads were tube rectified. Gold brittle logo along with small gray plastic feet on all head boxes. Head boxes have flat front lip. Thinner than normal top screen vent for 100 watt models. No vent on top of head boxes for models under 100 watts. Voltage and impedance selector on back will be a plug style, the shape and size roughly of a larger vitamin capsule style pill.

1967- early 1968: MK II labeling on all amps. Enlarged normal top vent screen on 100 watt models. Plug style voltage/impedance selector continued. Voltages for U.S.A. models set at 105 and 110 volts. Some filter capacitor cans not mounted on the top, but NOT the complete set of 6 as was traditional on all later 100 watt heads from later in 1968 and onward. Serial number scheme inconsistent with window-etched types or ink stamped being the norm. Gold brittle logo along with small gray plastic feet on all head boxes continues. Head boxes continue flat lip style.

Mid 1968-July 1969: JMP now labeled on front panel. Majority of amplifiers now used small, rounded black plastic on/off and standby switches. Voltages for U.S.A. selector now set at 120 volts AC. Mid ’68 marked the transition to the window-style voltage and ohm style selectors which is a one inch round black plug with a small square window to view the ohms or voltages selected. Fifty watt JMPs now have solid-state rectifier. Serial numbers now consistently stamped in engraved black on rear plexi panels. Mid 1968 marked the beginning of the 6 filter capacitors (typically 50 x 50 uf each, though some have been equipped with 32 x 32 uf as well) being mounted consistently on the top of the chassis. This configuration continued with 100 watt models until midway through the JCM 800 series. Gold logo along with small gray plastic feet on all head boxes continues. Head boxes revert to rounded-front lip style in early-to-mid 1969 before the end of the plexi era.

To buy a 50 or 100 watt?

Both will be powerful and of course loud. 100 watt amps can be generally thought of as punchier with a tighter bass response and of course more headroom. 50 watt amps can be thought of as more of a “blended” raw sound when the amps are turned up to distort with its particular tone. It’s a subtle difference between both but sonically they are different. One cannot say that an equivalent 50 watt amp will have more distortion than a 100 so don’t look for more gain to pop out of that 50 watt amp. Also, don’t think that the added two extra tubes in a 100 will cause more distortion. In truth, they are about the same but have a different feel and response.

Also, whether I play a 50 watt or a 100 watt plexi amp, I still need to use an attenuator such as the THD Hot Plate to bring down the levels a bit. The actual volume difference between a maxed 50 or 100 watt is only about a 3-4 dB difference! So don’t decide based on the notion that a 50 watt should be half as loud. I prefer the 100 watt sound personally, but many prefer the response of the 50 watt models. It’s best to experience them both for yourself and then decide.

Original European amp or made for export to U.S.?

In the plexi era, beginning in mid-late 1967, Marshall made slightly altered versions of its plexi amps for the U.S.A. market. These models can be identified by use of three toggle switches on the front rather than two for the European amps, with the extra toggle being a polarity/ground switch. This worked together with an attached two-prong AC cord and was used to eliminate any hum caused by a ground loop from the line. Built for U.S.A. export amps also did not have a variable voltage selector, but rather fixed voltages (the extra wire taps for other voltages was usually still available off of the transformer however) and sometimes mounted to a separate mini-board along with the polarity switch assembly. You simply plugged in your amp and chose the polarity setting that caused the least amount of hum. European amps were grounded, had detachable circular three-prong Bulgin connectors and no polarity switch on the front.

What kind of changes should I consider to make my plexi sound better? Should I modify it?

If you enjoy the various rock and blues sounds from the known players that have used Marshalls, you should know that many of these Marshalls got their tone in stock, albeit cranked form. There are small circuit changes that some people choose to make to fine tune their amps, but in general, I find it’s more important to focus on your entire rig or system and go through it before you look into performing major modifications to an amp. Certainly with collectability of plexi Marshalls being a major factor these days, I personally wouldn’t do much if anything to mine on the off chance that I may want to recover from my investment at a later time.

Also consider what are you looking for? For some people, it’s more gain, to others it’s to reduce the brightness, for others the amp may seem too muddy. I’ve been there. For gain, I chose to incorporate a clean-boost effect to increase my gain when I wanted without affecting the tone (you can read more about this in the Tips and Tricks for the Marshall Super Lead article). For reducing the brightness as well as overcoming what was to me a muddy sound that lacked definition, I did two final things. 1) I invested in a 4 x 12 Marshall basketweave cabinet loaded with Celestion Greenback speakers and 2) I invested in a quality pickup and tossed the high-gain ceramic pickup that was in my guitar. By not modifying the amp, but rather some of the items around it that was plugged into it, I found that I was and am able to achieve the smooth rock Marshall tones I’ve enjoyed listening to over the years.

How to check out a plexi for originality even if you’re not a tech!

Plexi BoardsFirst you should be familiar with what a Marshall plexi is and what it should look like. Basic amplifier with four inputs, controls for presence, bass, middle, treble and volume 1 and volume 2. Look at the front and back of the amp. The most common easily visible modifications are master volume controls (usually one extra knob installed in one of the four input jacks or a speaker jack if the modifier chose not to drill a new hole), effects loops (two extra jacks on rear), direct/line out (XLR or ¼ inch connectors), and of course the ever-popular mod in the ’80s, the fan mounted to side of head cab- mod. An extra switch sometimes accompanies this mod. In anycase, modifications are relatively easy to detect, but if you’re looking at a plexi amp and it’s being advertised as all original and you’re going to pay the price, you should do some additional checking of your potential amp.

Who cares about originality? Well, what about the output transformer? A swapped out output transformer for a lesser quality cheapo version will dramatically alter the tone and the value of the amplifier. Now with mods, my opinion is only that – an opinion, but modded amps are always worth less because they’re like a crapshoot. You never know what you really get, BUT from my experience especially with hot-rodded gain heavy Marshalls is that there is so much preamp gain that two things happens. First, the tone just loses punch because you’re no longer running the power tubes into distortion because if you try to do just that, your hot-rodded Marshall will start to squeal uncontrollably. Then second, you turn down the preamp gain or secondary gain to compensate but somehow the amp just doesn’t sound as good anymore…Hmmm…Now on to originality looking inside the amp.

Remove the back panel and look inside. A Super Lead or Super Bass will have three preamp tubes and a Tremelo model will have a 4th tube. Four tubes in a Super Lead or Bass means an extra gain tube was added or possibly it’s a tube for a tube-driven effects loop. Now look at the two transformers. The one on the far right that may be laying down or standing up is the Power Transformer. Examine the shine or lack of shine on that transformer bell housing and compare it to the output transformer, which is the transformer closer to the near center of the amp. Do they look similar or is one nice and shiny while the other is dull? It’s not a guarantee but if they look different, it’s a good bet that the shiny transformer is the newer replacement.

Now, let’s pull the chassis out of the head box by removing the four screws on the bottom of the amp. Have the owner do this and if he doesn’t want to, then it’s best to move on unless you’re scoring a deal of the century. If removing the chassis yourself, pay careful attention to the plexi panels. Don’t just slide out the chassis but gently lift it up slightly first so that the plexi panels don’t snag and crack against the aluminum shield plate underneath it.

If you’ve got an amp model with a vertical “stand up” style power transformer and therefore it is the same height as the output transformer, you can turn the amp over and rest it on its transformer tops to get a full comfortable view of the circuit layout. If you’ve got a laydown-style power transformer, use some books or other items to help support the amp so it can rest in the same way. Now first, carefully look at the circuit board. The majority of these Marshalls have red painted dye that was put onto all the solder connections including the pots, switches and jacks. Look for it everywhere. If you see plain silver solder, it’s the mark that some work has been done. OR what if you see two different shades of dye? Beware as some unscrupulous people have re-dyed the factory solder joints after changing parts.

Now given the fact that you’re examining an amp that’s 30+ years old, assume that of course it’s had some maintenance or repair. Now look for the cloth-coated wires from the output transformer that lead to the output ohm selector as well as the circuit and tubes (one wire each there if I recall). Do all the wires from the output transformer have the red dye mark as well? Are the cloth-covered wires? All plexis I’ve seen with original output transformers have this kind of wire. Do the same by looking at the leads for the power transformer.

If you’ve got consistent red-colored dye that is all the same basic color shade all around, then you’re in luck, or you’ve got a very well-done fake!

What!!? Well I haven’t personally seen one, but it would seem fairly easy to dress up a later metal panel Marshall amp with some reproduction plexi panels and then pass it off for 3 times the money!

O.k. on that note, there are a few other things that one can look for if you’re more of the technical type including the type of bias selector used and board color and whether it’s perforated or not. In general, the earlier boards were all perforated and a dark tan and brownish color. Then that transitioned into a darker tan non-perforated board. If you’ve got a light tan or crème-colored perforated board, this can be a warning flag that you may not have a real plexi. Also, regarding the bias selector, the stock original types for the plexi era are the slider types which are long metal pieces with a square slider that you move across to adjust the bias. The first of the screwdriver rotational types emerged either toward the tail end of the plexi era or right in the beginning of the metal panel era. I call these the horseshoe style-bias adjusters. They changed again in early 1972 to another similar but smaller circular bias adjuster.

Finally look at the inside of the chassis walls. Do you see any holes that appear from the inside, but not on the outside? Some are normal such as the spot where the tremolo and voltage selector areas are at. Usually those look factory made and are easy to identify compared to what someone may have done with a drill bit. In any case, seeing holes on the inside, but not the outside panel indicates a panel change.

You know with all this said, most dealers and people in general are honest, but you’ve got to be careful, especially with people that claim they don’t know anything about a particular amp they’re selling. It’s actually kind of fun looking these amps over – certainly cheaper than checking out cars, kicking the tires and what have you!

What’s so special about a plexi Marshall anyway?

Plexi Cloth LeadsMany things. First and most important perhaps is the sense of dynamics and rich harmonics. No large-production amp created before or since the early Marshall plexi series has been able to capture the feel of the player through varying degrees of dynamics and coloration from the (mostly) EL34-based tube circuits of these Marshalls. Call it a lucky accident with the folks at Marshall, but they were able to create amplifiers that really responded well to the guitars that played through them. A wide palette of distortion color that is rich and full and just powerful and timeless in tone is what these amps deliver. It takes some time to really get used to playing a basic amp such as a Marshall plexi. No multi channels or reverb or effects and no master volume controls. Turn up the amp and play – play hard and the amp rewards you with fullness of tone and smooth distortion. Back off your playing and the amp will respond, and move into lighter shades of overdrive. Roll down your guitar volume a touch and you’ve got a warmed up clean sound. There just isn’t anything like the ability to feel a set of power and preamp tubes overdriving together musically.

On a less-significant note as far as tone itself of the amp is solely concerned is namely the rich Marshall heritage. When you’ve had players from Hendrix to Clapton, to Van Halen and Page and countless artists in between and now – all put there sonic stamps of creativity through a plexi Marshall, that certainly says something.

Finally, certainly something special, but not unique to the plexis, is the build quality. These amps were hand-wired point to point, feature vastly superior transformers than production models of today and while it’s a cliché, it’s never been more true: “They don’t build ’em like they used to!”

Other than all that mentioned previously, there really isn’t much special about plexi amps!

What’s it worth? Where to find ’em?

Kind of a trick question, but in general if you’re shopping specifically for a plexi Marshall and want the best price and amplifier possible for your dollars, you’ll have to decide whether or not it’s worth it to you to spend some time to examine the market and see the trends. Obviously condition and originality are some key factors and if you’ve got a nice original plexi with all the components in place, those will command a premium over one that has had holes drilled into it, replaced transformers, etc. On that note, if you can forgive a previous mod-mark of some type, or are willing to deal with a fixer-upper amp you should find some good opportunities for good pricing. Realize that a fixer-upper is like anything else and you may end up investing more dollars to fix up an amp to get it up to shape then what a clean-original piece would have sold for in the first place. Think of this as similar to a classic car – you can purchase a beat-up classic car for a deal, but more often then not, buying a restored or extremely clean car in the first place – while initially at a higher investment in dollars – ends up being cheaper in the end. Fixing or restoring a classic car is not cheap and many of those little knick-knack parts can be very expensive. The same holds true, believe it or not, with vintage amplifiers.

On that note, I tend to stick to amps that are original in the first place without holes or replaced major parts (e.g. again, either transformer!) because no matter what you do to the amp to fix it cosmetically and/or sonically, the value and interest in the amp will be dramatically less in the end no matter what. I think this is an area that some private sellers don’t understand and learn the hard way when they finally go to sell their plexi Marshall with three leftover holes from former modifications and/or a replaced output transformer and then they discover they have such difficulty getting the plexi-premium pricing that they’re longing for!

From my experience, the higher prices paid for plexis come from vintage amp dealers and the lower prices are typically found from private party sales. That said, a dealer has its reputation at stake so usually there is more comfort involved with those purchases as well as possible recourse for misrepresentation or issues. Some dealers are also very knowledgeable and not only specialize but also work on and maintain these older classic amplifiers. In the case of a dealer offering full servicing with its amps for sale, a higher price can often be justified and worthwhile. In other cases, a dealer may just be providing a high price simply from the fact that quite honestly, the plexi shopping market has really dried up in terms of really nice amps being available and the dealer may not be in any hurry to let go of the particular amp, knowing full well that its value will only go up as it sits in the shop.

You’ve got all sorts of options when actually looking for a plexi Marshall – you can check your music stores in your area, possibly the classifieds in your local paper, but beyond that you also have the Internet as an option which can open up new possibilities. In terms of finding plexi Marshalls as of this updated writing (5/02), they just aren’t around much so don’t get discouraged and be patient. Bulletin Board forums and various dealers are available online and are a resource. In the case of bulletin boards, these are great for meeting and conversing with other buyers and sellers of Marshalls as well as good avenues for information.

You also have the Ebay option. I know that there is an element of concern many times purchasing something you can’t hear or play through in person, but I’ve found that personally spending time with sellers by asking important questions through e-mail or phone correspondence can do a lot to ease any possible concerns. Certainly I’ve had good luck and experiences making purchases from Ebay, dealers listed online, as well as through folks on forums or bulletin boards, but I’d say it’s again because I try to be very careful and ask very critical questions. If a seller doesn’t know a particular answer to a question, I try to guide them through a detailed description of what I’m looking for over the phone. If a seller is unwilling to allow this scrutiny, I’ll pass on the transaction – either the seller in this case has something to hide and may be looking for a more naive customer or he/she is just not willing out of laziness or whatever reason to deal with the questions – that’s o.k. in the case of the second scenario, but it’s o.k. for me at that point to take my business elsewhere! Of course you always have to be careful, but at the same time I’m a believer that 95% or more of the folks out there are basically trustworthy and some correspondence with the seller can generally help give you a feel for the person.

Purchasing outside of your home country: Two words: Buyer Beware. I don’t recommend you use wire services for payment. Use a credit card that will provide you some protection just in case.

How reliable will it be? Considerations when purchasing vintage Marshalls!?

There are no hard and fast rules here. It’s an older piece of equipment and obviously will at some point require servicing and maintenance. Fortunately old Marshall plexis are amazingly simple circuits and some time spent in general maintenance when you first obtain your amp – areas like retube/rebiasing, retensioning, cleaning all tube sockets, cleaning the jacks, retensioning and cleaning voltage and ohm selector sockets, etc. – will all go a long way to providing many years more of faithful service. Because these classic amps were built well and use good components in the first place, Marshall plexi amps are overall very reliable and can take a beating. If you have a tech you trust, perhaps have them look over an amp before a purchase if possible and they can give you an idea of what you’re getting into.

That said, if you have concerns or excessive worries about potential problems and just have a worrying personality, you may be better suited to purchasing a reissue model or modern boutique clone. While reissues are different in many ways, they can be worked on to warm-up the tones a bit, though its my experience that they won’t ever duplicate the original – they can get reasonably close. For more information about the original vs. reissue debate, check out the article on that exact subject under the “Amps” pages.

In the case of modern boutique clones, these are excellent choices for that person that wants an out-of-the-box new amp with classic tones and with a warranty. You need to be careful with boutique amps however and do your research because they may not all be up to par in terms of build and sonic quality and may instead be capitalizing on the boutique category in order to maximize their profits. There are some however that we have NO problem recommending, including those built by George Metropoulos. One boutique clone of a JTM 45 that also delivers the goods, is built by Mojave Amp Works. Check it out at if this is something of interest to you. Full details and photos are available at the company’s site.

For me personally, I really enjoy not only the tones of the older original Marshall plexi amplifiers, but I also play them because of their rich history and heritage. It’s always a thrill to fire up the ’68 plexi Super Lead (or even my ’72 metal-panel which is a great amp but of course worth less) and extremely satisfying to note that its array of tones are still very relevant and useful in the music I create today. Knowing that so many legendary players from the past played (and in some cases still play) similar Marshalls is an extra bit of a kick I’ll admit.

That concludes this first installment of the Marshall Shopper’s Guide. Next time, we’ll cover the metal panel years, including the start of the master volume series and some of the other interesting changes that occurred in the models from the time of mid 1969 through the JCM 2000 series. Happy Shopping!

6 thoughts on “The Marshall Shopper’s Guide Part 1: Marshall Plexi Era

  1. I found this article very interesting, I really do love Marshalls but I’ve never had a plexi amp. Like someone says “It’s never too late”!!! :-)

  2. Thank you. They are fun – and these days there are MANY great amp makers that build designs that sound just like the originals as well (especially good to note since the originals are scarce and valuable).

  3. “These amps were hand-wired point to point”
    Great article, just a minor point on terms. In my experience, the term point-to-point refers to circuits where the components are wired directly to each other on a wiring strip, as opposed to the tag boards used in amps. The Vox AC4, for example, is considered point-to-point. The Fender Bassman, not so much.

  4. You are absolutely 100% correct. True point to point like in old Valco amps can look a bit messy. Marshall used the term point-to-point with its marketing of the handwired series, so I think the term has shifted a bit in meaning over time.

  5. Interesting article… Some points though… The reissue JTM 45/Bluesbreaker does not need to be “converted” from 6L6/5881s to KT66s. The KT66 is a 6L6 type tube to begin with so no converting needs to be done just bias for the tubes themselves. Plus, where the Bluesbreaker reissue combo is physically smaller than the originals, the KT66 wont fit as it is too large… The JTM 45/100 (and early MKII up until ’67) amps used KT66 power tubes. ’67 marked the switch to EL34s across the board… The tube rectifier was phased out of the 50 watt in favor of the diode sometime in ’66… The earliest 45/100 (before launching into full production in late ’65) amps had two JTM 45 output transformers rather than the one larger and had an absolutely mammoth power transformer (the unicorn of the 100 watters). I only know of two in existence… One of which was wrecked (but still survives) by The Who… And those who don’t really want to pay a king’s ransom to own a Plexi and are concerned more with the tone rather than the value should check out Metropolous amps. George Metropolous builds a fantastic Plexi clone… One last note: For those looking for “that tone” like Clapton, Kossoff, and tons of others had, get a clean power booster. The standard of the day was the Dallas Rangemaster Treble Boost. It was the secret weapon of the day. If you want to get the best out of a Plexi (or any pre JCM 900 Marshall) then a power booster is a wise investment. The T.C Electronics “Spark” is a great unit. The lower priced EH LPB1 is also very good though I’m not sure if the new versions are true bypass. I know my original wasn’t… Anyhow… Have a good one.

  6. Good catch on the tube language for the KT66 as you are correct in that it’s not a conversion, but rather an upgrade. I also agree 100% on the Metro amps. We checked out one of his 12xxx ’68 replicas when they first came out and were blown away. As for boosts, I’m a bit biased but the Time Machine Boost is a collaborative effort I did with Robert Keeley many years ago – it has two channels so you can do any combination of rhythm and lead boosts. The vintage germanium channel is Rangemaster like but with a few selections and mods and the modern channel is a pure clean boost done with dual JFET and voltage-doubling for insane headroom and punch.

Leave a Reply