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45 Degrees of Tone: The JTM45 Roundup

Nearly 50 years since its creation, the Marshall JTM45 remains both a relevant and near-perfect example of what a great rock ‘n’ roll tube amp should be.

Nearly 50 years since its creation, the Marshall JTM45 remains both a relevant and near-perfect example of what a great rock ‘n’ roll tube amp should be.

It was originally built around the design of one of Jim Marshall’s favorites, the Fender Bassman; like the Bassman, the JTM45 was actually a fantastic guitar amp. Because of its consistent popularity, Marshall has offered a reissue version of the head— more than 20 years after production of the original JTM45 ceased. While the reissue is built with modern components and assembly techniques, it retains much of the tone, responsiveness and character of the original, hand-wired versions of the early days. No wonder builders today still carry on the tradition of the JTM45, and guitarists continue to seek out the pure simplicity and touch response of this tone machine. To celebrate the JTM45, I got together with my Sunday afternoon amp group, after contacting a handful of respected amp builders who sent us their versions of the amp. We fired them all up alongside an original and a reissue JTM45 to take a listen—and to enjoy one of the best amps ever designed.

About the Authors

About 5 years ago, while playing a 9/11 benefit

show, I had the good fortune to meet two people

who would not only profoundly impact my life

with tube amps, but would become lifelong

friends. John Rossi and Tony Burns were there

that day; Tony, a killer player and a regular on

the Tempe/Phoenix music scene, and Johnny, his

friend and amp tech, making sure Tony’s amps

were running well in 115 degree heat at the

outdoor amphitheater. When I saw Tony’s wall of

Marshalls next to my backline of Marshalls, it was

an instant conversation starter.

We spent time between sets that day discussing

the various finer points of our amps and gawking

at each other’s rigs. The show went great but my

’67 Super P.A. felt a bit stiff, and wasn’t reacting

in the most flattering way. This incident proved to

be the catalyst, as Johnny was an underground

semi-retired tech and ultra-fanatic Marshall enthusiast,

and he had some ideas that he wanted to try

out. He invited me over the following Sunday to

check out the amp, and to experiment with various

preamp and power amp tubes while BBQ-ing and

having a beer. Tony was there, and it became clear

that we all had a deep respect for these amps;

rather than modify them, we wanted to bring

them back to their former glory. After five years,

and dozens of hacked-up Marshalls coming back

from the dead, here we are. Over that time we’ve

learned more about these amazing amps than any

of us ever anticipated, and we’ve have had a blast

in the process. I have no doubt in my mind, based

on my readings of the various amp forums, that

there are plenty of groups just like us all over the

world doing the same thing.

The Lineup

The lineup consisted of our own 1965 original and 1990 reissue heads, two

MetroAmp JTM45s (a kit version as well

as the GPM 45), a Germino Classic 45, a

Wallace Amplification BKW45 and Mojave Ampworks’ new Special Edition Plexi 45

head. After searching through our collection

of cabinets, we settled on both

an eighties Marshall JCM800 4x12 with

blackback 25s, and a Mojave 2x12 cab with

1963-era Celestion Alnico Blues. It may

sound strange that there were no pinstripe

or basketweave cabs used for the roundup,

but that wasn’t for lack of trying. Among all

the members of the amp group, we actually

have a pinstripe, a basketweave and a variety

of Marshall 4x12s, but for some reason

we always come back to the early-eighties

JCM 800 cab with blackback 25s.

That particular cab has more clarity, tone

and authority than any other, and it remains

our favorite in the bunch—despite the cool

factor of the older cabs. The 2x12 with

Blues was a natural choice, as that flavor

shares similarities with the mid-sixties

Marshall cabs and is also a popular speaker

configuration for Bluesbreaker combos. The

guitars we used were our standard array

of Les Pauls from the ‘70s, ‘80s and 2000s,

as well as a newer 2008 Fender Strat and

two early-seventies Strats. With everything

in the room (it was quite a sight!) we were

ready to begin.

Original 1965 JTM45

To get our ears accustomed to the JTM45

sound, we began by firing up our ’65 head

with a Les Paul. Normally, this head has EL34s

in it, but we borrowed the Genelex KT66s

from the Mojave and biased the amp to

accommodate them. It made sense to us to

use KT66s, because they were what the amp

was designed for. With everything looking

good, we flipped it from standby and beheld

the beauty of this vintage masterpiece. It’s no

wonder players and collectors are paying big

bucks for these amps; everything we played

through it sounded incredible.

What was amazing was how much of a rock ‘n’

roll amp this really is. Considering how long

it’s been since it was conceived, the amp’s

sound remains surprisingly current. The distortion

is organic, full-bodied and earthy, and

it allowed the personality of the guitar and

player to shine through. While it was very easy

to play, this is an amp that still requires a level

of discipline and control to fully harness its

capabilities. It makes sense that players who

want to be heard would play on this style of

amp, because like it or not, whatever you play

through the amp is… well, amplified. It just

comes out better.

We played through it for a good long time,

switching guitars and speaker cabinets to hear

it in as many different configurations as possible.

Whether it was a Strat, a Les Paul, a 2x12

or a 4x12, the sound was always remarkable—

perhaps the very definition of great tone.

Subjective? Yes. Brilliant? Absolutely. Rolling

back the volume on the guitars exposed a

beautiful clean tone that was harmonically rich

and defined, never muddy or dull. Even with

the guitar’s volume knob all the way up, the

dynamic response of the amp, and the way it

musically fed back, was awe-inspiring.

Once we had established a base tone for comparison’s

sake, it was time to play and listen

to the other amps. Before I break down each

individual amp and builder, I must observe

that each and every one of the amps had ridiculously

good tone, and they all sounded like

JTM45s, but each had its own unique voice.

Aside from the reissue Marshall, all of the

amps are hand-wired. The reissue Marshall was

of PCB-construction, and used the standard

parts and components that Marshall was building

their amps with during that era. I spoke

with Mitch Colby from Korg USA (Marshall’s

US distributor), who told me that the reissues

have not undergone any significant changes

since their reintroduction 20 years ago. While

they are using the components that Marshall

builds with today, they should yield very similar

tones to the earlier reissue amps.

MetroAmp JTM 45 Kit and GPM 45 Custom Build

George Metropoulos is no stranger to the

world of Marshall amps or to the online ampbuilding

community. Having run MetroAmp

for some time now, George offers everything

from fully built replicas of many classic

Marshalls to ready-to-build kits and hard-tofind

replacement parts for vintage Marshalls.

A player, George honed his amp-tech skills by

adopting a DIY approach, taking care of his

own amp repairs on the road. This extended

into repair work at home, and then really

took off when amps began coming in for

restoration rather than simple re-tubing. After

his ’73 Super Lead was stolen from a gig, he

realized it might be best to leave the valuable

amps at home, and so he embarked on

a never-ending quest to replicate the tone of

the old Marshalls.

Like all the builders in the roundup, George

is passionate about vintage Marshalls and

obsessive over the details that make these

amps so coveted. We received two amps

from Metro: the JTM45 kit (which can be purchased

already assembled for an additional

$400) and the GPM45, George’s custom-built

JTM45 using NOS vintage parts. When we

fired up the MetroAmp 45s, it was clear that

they both came from the same camp. Both

amps were meticulously built and incredibly

precise in their layouts. The main physical

differences between the amps came down

to the caps, resistors and tubes. Both amps

shared the same iron and layout, so they

also shared a lot of the inherent tone in their

circuits. As George is a fan of the mid-sixties

JTM45s, Metro’s transformers are based on

the Drakes, rather than the earlier Radio

Spares iron. Still, there was no question that

the GPM45, which included NOS Phillips

mustard caps, Allen Bradley carbon comp

resistors and a gorgeous set of Genelex

KT66s, was sweeter sounding.

While those differences accounted for a tonal

upgrade, what made the differences even

more compelling was the way they affected

the touch factor of the amp. Much like our

’65, the custom-built Metro had an ease

about it that felt like a broken-in vintage

head, making it a breeze to dig in, or to lay

back on the strings and feel the amp act as

an instrument. It was truly inspiring. Of all the

amps in the roundup, this amp sounded most

like our ’65—frighteningly close! I should

mention that the Metro kit version was actually

plugged in first, and before comparing

it to the GPM45, we all agreed we’d be

thrilled to have one in our collection. We may

be splitting hairs here to some degree, but

knowing that anyone can buy a complete kit

for under a grand, and have that kind of quality

and tone—that says a lot.

JTM45 Kit:

GPM 45 Custom Build:

Wallace Amplification BKW45

Brian Wallace has electronics in his DNA.

His father, an electronics engineer, and his

grandfather, an RCA tube repairman, were

both instrumental in his early education

and development in tubes and electronics.

When he was young his father gave him a

75-in-1 electronic projects kit and further

encouraged Brian by letting him watch as

he built his own projects. Like all of the

builders in the roundup, Brian is a player.

He began modifying amps in 1974, when

he removed the speakers and baffle in his

Checkmate amp and replaced them with

a baffle he created and some purchased

speakers—altering the sound of the amp

and thus beginning his lifelong journey.

In 1995, he was approached by Guytron

Amplification to help out while they were

getting started. A positive experience, it

propelled him to the next level and led

to the creation of Wallace Amplification,

which now offers several amp models as

well as replacement transformers under

the Marstran name.

Wallace’s first amp is the BKW45, but he

is more than a clone maker. Recently he

introduced the Abaddon, which is a 50-watt

master volume head consisting of four

gain stages in the preamp. There is much

more to come, including a line of pedals

and a reissue of the Fuzz Ace pedal he

made back in the early 90s. The BKW45 is

a unique flavor of JTM45. A hair darker in

tone and possessing slightly less gain than

all of the other models, including both the

vintage and reissue Marshall, it yielded

enormous bloom and a bold, thick, sustaining

quality. Even though there was a little

less gain, it didn’t affect playability, and we

never struggled with the amp. It was one of

the rarest qualities I’ve experienced in an

amp, and certainly an unexpected bonus.

The Wallace had a magical ability to push

notes through loud and clear while still being

able to dish out gritty and harmonically pleasing

chords that didn’t fight the non-perfect

intervals they were built on. This all came out

of an amp that was using tubes you can buy

today without breaking the bank.

Speaking of breaking, check out the sidebar

on what the BKW45 was subjected to by

UPS en route to our roundup. In spite of the

gorilla treatment it received, the amp arrived

without shattered glass and performed flawlessly

throughout the entire set of three

sessions of playing and listening. That’s a

testament to a solidly built and roadworthy

piece of equipment. And one look inside the

amp will show what a dedicated and precise

builder Wallace is. In tone and build quality,

the amp is a work of art.

Ever wonder what could happen to your amp in shipping? In the case of Brian Wallace’s BKW45 amp, UPS had a field day, and decided it would be a lot of fun to throw it around. When the amp arrived, it was packed neatly in a new cardboard box with padding inside suspending the padded road case that housed the amp. That’s double-boxed and protected by a case built for heavy abuse. Sadly, it took one good slide down the end of a ramp and collided with either another box or the wall of the truck. Though the box didn’t show any signs of abuse on the outside, it was clear that something had shifted when I opened the case. Take a look at this picture of the damage and the way the entire amp was shifted to one side because of the impact. Believe it or not, the tubes didn’t shatter and the amp worked fine, but it was cosmetically damaged by a broken front Plexi panel. This isn’t the first time this has happened, but it’s the first time I’ve seen it happen with this type of road-worthy packing. Let this serve as a reminder to always insure your amps, as the shipping company can’t tell if you’ve got a bag of peanuts in a box or an amp that was lovingly built by somebody like Brian.

Germino Amplification Classic 45

Greg Germino is another lifelong guitarist

who was bitten by the tube-amp bug

after catching the Allman Brothers Band

back in 1972. He was so inspired by that

show that he switched over from acoustic

to electric guitar and began taking electronics

classes in high school. In 1979, he

requested schematics from both Ampeg

and Unicord (Marshall’s US distributor at

the time) and began his hands-on education

with tube amps. He spent the ‘80s at

an electronics job, and by the early ‘90s

he was moonlighting doing tube amp

repair for a few music stores. He continued

to play live with both 50W and 100W

Marshalls during that time and moved to

Durham, NC to work at Bull City Sound—

working on tube amps from the big-name

amp companies.

This led to Greg’s being commissioned by

Mojo Musical, where he built their Tone

Machine amplifier. The following year,

2002, he began work on the prototype of

his Lead 55 amp, which debuted in May

of 2002. The Classic 45 model is based on

the earlier R/S-style output transformer,

rather than the Drake 1202-103 used in

the ‘65–’66 era, and the circuit is exactly

what you would find in an earlier original.

The R/S OT is supplied by none other than

Chris Merren, who is highly regarded in

the world of Marshalls, and known to make

some of the most accurate transformer replicas

out there.

The Classic 45 was the only amp in the

roundup that used 6L6 power tubes. Greg’s

decision to use them was a combination of

staying true to the earliest tubes Marshall

used on the original JTM45 amps and his belief that the current crop of 6L6s sound

and perform better than newer KT66s. NOS

and vintage 6L6s are also less expensive

and more plentiful than NOS KT66s. Our

immediate response to the Classic 45 was

that it was a lively and aggressive amp, with

tons of power that made the pick explode

off the strings. In ways it reminded us of

our favorite ‘67 Super Bass in its volume

and attack, but it still retained the sound

of a 45. It may very well have been the

loudest amp of the bunch, and that volume

translated to a feeling of excitement that

made the amp extremely fun to play. It

was present without being shrill and had

a super-tight bottom end, no matter what

guitar we played through it. While the

Classic 45 had tons of natural gain on tap,

it also cleaned up nicely when rolling back

the volume on the guitar, revealing a bright

and sparkly chime. This amp is a real beast,

and it could hold its own against 100W

amps without flinching.

Mojave Ampworks Special Edition Plexi 45

Anyone familiar with the JTM45 would surely

be jealous of Victor Mason. Not only has

he seen more than his fair share of vintage

Marshall, Vox, Hiwatt and other rare treasures

come through his shop, but Victor recently

acquired 26 of the all-time greatest JTM45s

ever assembled via the Kronemyer collection,

and he’s got the pictures to prove it! This is just

one of the factors contributing to the obsessive

nature of Mojave (and the associated Plexi

Palace). Having been around for over a decade

on the internet, Vic has been repairing, restoring,

buying and selling vintage Marshalls for

quite some time now. Stemming from his early

desire to find out how EVH created the classic

brown sound, Victor embarked on his journey

through countless hours of digging into vintage

amps and learning where their strengths and

weaknesses lay. Mojave now offers an entire

line of amps to serve the classic Marshall tones

and well beyond with innovative features and

designs. The Mojave Plexi 45 also has two very

unique features over a stock JTM45. First is a

simple feature to allow volume control by way

of throttling the power level. Second is a line

level output, which is adjustable and incorporates

a ground lift.

Standing apart cosmetically from the rest of the

amps, the Special Edition Plexi 45 is built on

the same footprint as the Coyote and Scorpion

designs, with a white-and-black color scheme

and chrome hardware. The head is built with an

open grille cage that allows for maximum airflow

to keep the set of completely NOS glass cool.

The 45 supplied for the roundup consisted of

a pair of 1970 NOS Genelex KT66s, 3 Mullard

12AX7s and a Mullard GZ34. Like the Germino,

the Plexi 45 is based on the R/S transformers,

which are custom wound by Mercury Magnetics.

The chassis is a thing of beauty; the .09” thick

aluminum, with a high tensile strength and welded

edges and seams will ensure it will not flex,

bend or develop fatigue, like the early, folded,

softer chassis, and will prevent the heavy transformers

from causing the chassis to sink in and sag. Mojave deviates from the original JTM45

by using modern, tight-tolerance parts. Custom

manufactured caps and metal film resistors allow

each amp to sound as close to the one built

before it as the one after it. Consistency is something

that Vic definitely strives for, and it shows

in the build quality and attention to detail, and

the desire to add convenient functionality to his


We found in testing that not only did the

amp have an extremely low noise floor, but that

it was an authoritative and powerfully voiced

amp. There was definitely something different in

the tone of the Plexi 45; it was cleaner sounding,

but still very bold. Having been to Vic’s shop,

I was fortunate enough to play one of the 26

JTM45s he had acquired, and I’m positive that

the experience with those amps had more than

a little to do with the design of the custom R/S

transformers made for his Special Edition model.

The amp is built like a tank.

Marshall Reissue JTM45

While the reissue looked very similar to

the ’65 on the outside, especially due

to the fact that it’s already 20 years old,

the differences on the inside were quite

pronounced. Assembled with more modern

methods, and using a PCB rather

than hand-wired turrets, you could easily

be fooled into thinking that it wouldn’t

perform like the others. This particular

amp was the only one in the bunch to

use EL34s rather than KT66s or 6L6s, so

the sound was definitely different. It was

incredibly loud and focused sounding,

and actually had many of the characteristics

of a Super Lead. The sustain and power of the amp was incredible, and for

an amp that can be found used for around

$1000, this is a sleeper bargain. Marshall

has taken some flak for their amps sounding

stiff and cold from the factory, but with

a little attention–slightly hotter bias and

good tubes–this amp is a monster. And just

because it says it’s a 45-watt amp, don’t

harbor any illusions that it would be a good

bedroom amp. This is a loud and powerful

beast, and a tone machine as well.

The Blindfold Test

As a final, fun test, we did a blind study, to see

how accurately I could identify each of the various

amps in the roundup. Johnny and Tony set

up the group of amps, and I sat in a chair with

my back turned away from them. With the guitar

plugged in, they began to fire up the various

amps, and we got rolling. Out of all the amps,

I was always able to distinguish the Wallace

BKW45, due to it’s slightly darker sound. The

Metros were also fairly easy to spot, but I ended

up guessing the kit as the custom build and

vice-versa. The ’65 was also an easy amp to recognize,

but as ear-fatigue set in, the lines began

to blur substantially. Pretty soon, I was confusing

the Germino for the reissue JTM, the Mojave

Plexi for the Wallace, and the Metros for the

real JTM. It just goes to show you that all of the

amps performed remarkably well, and you can

be fooled when you’re not seeing what you’re

playing, so never discount a PCB reissue head

as a second fiddle to the real thing. In the mix

of a band, these differences become small, and

any one of these amps would hold their own

any day of the week.


To have the opportunity to play through

so many variations on a classic theme was

not only fun, it was educational. Each

one of the builders excels in creating

their own unique version of the great

rock and roll amp that Ken Bran, Dudley

Craven and Jim Marshall built back in

1962. While like all Marshalls, the JTM45

went through changes in tubes, components

and designs over its lifetime, there

is a trademark flavor and color that still

can be found in all of them. Not everyone

can afford a vintage 45, but with the

help of these builders we have the opportunity

to get into that sound and have

build quality that will last for years.