Marshall JMP 1987 50w tube guitar amplifier 1960A 4x12 speaker
cabinet
Last Update 05/31/2022
My guitar playing brother - who is very good at spending other
peoples' money - had been badgering
encouraging me to get a Marshall amp. A
vintage Marshall Major turned up at the store and my brother encouraged
me to buy that amp. He used to own a 100 watt Marshall head and
by the time it got a good crunch it was unbearingly loud. One of
the reasons I sold my 60 watt
Mesa Boogie MkIIa was it was too
loud. Reminding him of those amps, I told him that a 200w
Marshall amp was impractical. Those things were good for
concert arenas but way overkill for a recording or club gig
environment. Some years later, this Marshall
1987 50w head with 1960A 4x12 cabinet turned up at the same
store. The small Marshall logo and tethered power cord gave away
its
vintage. Trying it out, it got a good crunch at a more reasonable
volume than the way-too-loud amps we both used to have. The
asking price was a bargain back then compared to the prices they are
commanding on today's vintage amp market.
The store explained to me that two of the speakers in the cabinet had
been reconed,
but they couldn't get the cabinet to sound right. I had a good
idea why it didn't sound right, and sure enough after I got it home I
found that one of the speakers in the cabinet was wired out of phase -
yeah that will screw up the tone. When I corrected the wiring,
the cabinet sounded MUCH better. I knew those guys at the store
were competent and was surprised they didn't check for phase.
Going by the serial number, the amp dates to 1975. It's a PC
board amp and not point-to-point (PTP) like the earlier
Marshalls. The guitar community prefers
point-to-point Marshall amps due to the hype that PTP "sounds
better". Frankly, the guitar playing community takes far too many
myths like these
as gospel. Being an EE, I'm well aware that PC board design done
the wrong way will ruin the sound of the amp. But done right the
amp will sound great. While Fender and Vox in the 60s and 70s did
a PC board amp design the wrong way, no one ever complained about Mesa
Boogie
amps that didn't have PTP wiring. Marshall PC board amps sound
great and were a bargain compared to earlier PTP amps but as this is
becoming more common knowledge the value of these amps have crept
up. Put a crappy guitar through
this amp then through a crappy speaker cabinet, and yes it will sound
like a dog. By this time I had good guitars in my possession and
was gaining experience with different speakers. So I had
little trouble getting the guitar tones associated with this amp -
texas blues, southern rock, early Bad Company, 70s hard rock.
When I bought the amp, it already had three modifications:
- Original 6550 power tubes replaced with EL34s (requires a circuit
change)
- Post Phase Inverter Master Volume (PPIMV)
- Two channels converted to single channel with cascaded input
triodes
The amp also had the original speaker impedance selector which has a
history of going bad, which risks running the tube power amp without a
load and POOF the output transformer is toast. The original OT
was intact so I quickly took the amp to have a new and better speaker
impedance selector installed. The amp tech doing the work
recognized his work on the modification - he had modified the
amp. His memory is hazy but he believes the PPIMV circuit is the
Ken Fischer design. The amp is easily reverted to stock as the
tech carried out the modifications without altering either the front or
back panel.
When Marshall amps were imported to the US, EL34 tubes more prevalent
in the UK were in short supply in the US back in the 1970s. It
was not possible to import tubes between two countries due to rough
shipping, which can break the vacuum seal in the glass dome and ruin
the tube. With the 6550
power tubes more readily available in the US, they were installed in
Marshall amps in the US with minor circuit changes. There is a
tone
difference and players preferred the tone of the EL34s in the UK
amps.
The power tubes weren't directly compatible without changing the
circuit, but many
players opted to have their amps modified to accomodate the EL34 tubes,
which became more available as time went on.
The unmodified amp was a non master volume (non-MV) amp, and many
players liked the sound of the amp turned up but the volume was way too
loud for anything but large halls and concert arenas. Marshall
introduced master volume amps during 1976, but their implementation
wasn't ideal as the tone suffered. Techs like Ken Fischer later
uncovered a better solution in the PPIMV. The reason why the
non-MV amps sounded great when cranked was because the distinctive
Marshall crunch was a product of overdriving the power tubes and the
phase inverter (yes the phase inverter DOES impart its tone when
overdriven). Marshall's master volume solution inserted a volume
control BEFORE the phase inverter, yielding a wimpier tone even with
the preamp tubes overdriven. Ken Fischer's solution placed the
volume control between the
phase inverter and the power tubes, so the phase inverter
continued to receive a hot signal thus better tone. This solution
however does require more parts.
The final modification involved cascading the two input triodes to
achieve a high gain sound. This duplicated the configuration in
later Marshall amps. The downside is the amp is no longer a two
channel amp so you can't use the "jumpering channels" trick, but the
gains are better. Two of the four input jacks were disconnected
with the removal of the second channel. The remaining two were
wired so one jack gave you the stock input configuration, while the
other jack gave you the raunchier high gain sound. It isn't the
atypical Mesa Boogie high gain sound, but I actually like this
modification better. Unlike the Mesa Boogie high gain
architecture, you can get different tones on this amp that are not just
high gain. I found a setting that is ideal for a touch player,
which is my style. That's something the high gain Mesa Boogie
will not do. Hard playing breaks the amp into crunchy
overdrive, while lightly stroking the strings cleans up the tone.
The dynamic timbre is very controllable with just fingers, and the
relative volume stays the same. It's even better with the 65w
speakers. That's something the high gain Mesa Boogie amps will
not do, not even their texas blues Lonestar amp. No
need for channel
switching! When I was performing ZZTop's "La Grange" with the
southern rock band, I could play the clean tone during the intro then
go to that raunchy sound without channel switching. That was
convenient. And not enough players have an appreciation for touch
playing. This modification also gives a nice articulation with
muted and "chicken" picking.
It wasn't until later that I learned what that 4x12 cabinet really
was. Checking the datecodes of the speakers, I determined that
the cabinet dated to 1970. It did have the metal handles that
identify these early cabinets but I wasn't aware of them at the
time. Checking further, I discovered that the Celestion speakers
- 25w "greenbacks" - were the highly sought after "pre-Rola"
speakers. Rola was a plant where all Celestion speaker
manufacture was moved to by 1971, and the label on the back of the
speaker magnet identify them as being made at the Rola plant.
Players noticed a change in tone, and found that speakers in the older
cabinets sounded different (I won't say "better" because this is highly
subjective). "Pre-Rola"
speakers can be easily identified by the label on the back of the
speaker, which is missing the "Rola" in the title. In addition
the construction of 4x12 cabinets back
then was different, which impacted the tone. So I found myself
with a highly desirable vintage 1970 Marshall 4x12 cabinet with highly
desirable
"pre-Rola" greenback speakers. The store didn't know what they
were selling.
At first I thought it was one of those custom color cabinets with its
dark green tolex, but I later learned that was the stock color tolex
back in 1970. The tolex on the amp is black and doesn't match,
but at a distance they are so close in appearance that they look the
same.
Needless to say, that Marshall 4x12 has lots of friends. Every
guitar player I knew who owns a newer Marshall 4x12 and has tried my
cabinet has
loved the sound. When I was in the
southern rock band, our guitar player borrowed it for a week and he
begged me to sell him that cabinet. By then I knew what it was
and I politely told him that the cabinet was not for sale. He
sought something similar; he landed a cabinet made in 1972 but it
didn't sound like my cabinet - different construction and different
speakers. He's still looking, but they're hard to come by as
players hang onto these
cabinets.
Later I realized that my brother's 4x12 cabinet - which was long
missing its original grillcloth and piping - had metal handles and
grooves where the original piping
used to be - same as my cabinet. His cabinet was also an early
one like my 1960A slant cabinet except his is a 1960B straight
cabinet. Between my brother and me, we now had a full stack of
highly
desirable 4x12 cabinets!
Here's a demo
of my brother playing his '69 Les Paul Custom through my Marshall amp
through his 1960B cabinet loaded with Celestion Vintage 30s. His
guitar had been modified with brass nut, jumbo frets, bridge is a
replacement wih larger mass saddles, bridge pickup is early 80s SD
"Jeff Beck" pickup, and his signal chain is his Mesa/Boogie V-Twin
pedal through my reissue Fender
Reverb. Recorded with a single Audio-Technica AT2021 about a
foot from the cabinet, haas effect post processing added for subtle
stereo ambient effect (provided by my Yamaha E1010).
Man does that sound sweet - I still haven't been able to duplicate that
with a modeler.
The southern rock band I was playing with was playing a large venue
with a stellar
in-house PA system. I had been playing guitar through my Vox Tonelab SE amp modeller
in my
keyboard amp/speaker (I like a simple setup, one amp/speaker saves time
on setup and cartage), so for giggles I decided to drag out the
Marshall
head and 4x12. That was a mistake, as everybody raved about how
much better they could hear me and they wanted me to use that setup at
every show. I didn't really want to gig that vintage 1970 4x12
cabinet and scruff up the cabinet more, and I didn't want to risk
blowing those irreplaceable speakers (the original supplier of the
speaker cones - Pulsonic - lost the "recipe" to the paper cones when
their factory was destroyed by fire in the 1970s). I had two
other Marshall cabinets with 65w and 75w speakers but they didn't get
the southern rock tone like the greenbacks did. Neither did my
brother's Marshall cabinet loaded with vintage 30s. The 75w
Celestion speakers sounded so close to the 65w Celestion speakers in my
1960B
cabinet that the 75w speakers were redundant. I wound up putting
the
75w speakers in my Rhodes piano (why should guitar players have all the
fun?), and decided to load the now empty
cabinet with reissue 25w greenback speakers and gig the newer
cabinet instead of the vintage one. Comparing the vintage and
reissue cabinet/speakers... there is a difference in tone. The
difference is slight but the reissue speakers still got that southern
rock tone. Why do they sound different? Could be the
speakers, could be the cabinets (old vs new are different construction)
but I haven't gotten around to swapping speakers between cabinets
yet. I definitely prefer the pre-Rola speakers but for club work
the reissues are sufficient. Many players complain that the
greenback 25w speakers lack some bottom end, but that can be an
advantage depending on the rhythm sound to fit the song or making the
guitar lead be heard in a mix without turning it up.
One other accessory proved very useful. My Groove Tubes
Speaker
Emulator did an uncanningly scary good job of emulating the sound
of my cabinet through a flat frequency amplifier like my keyboard
amp. Like my Hughes
& Kettner Red Box, I had options for recording or for leaving
the guitar cabinet behind for a gig.
A very fine vintage package... this one isn't going away.
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