Marshall Amplification JTM45 User manual
From the Chairman
Congratulations on your purchase of the limited
edition reissue of the offset JTM45 halfstack. The
original versions of this amp and cabinet were built
back in 1962, the very year in which Marshall
Amplification was born. In fact, the offset head was the
first version of the JTM45 my company made and only
a mere handful of these heads and cabinets were ever
constructed. In case you are wondering, the reason the
amp's chassis was offset like this was to help ensure
that the head balanced properly when carried. Despite
the practicality of this design however, we quickly
discovered that most people preferred the symmetrical
look of a centrally placed chassis, so that’s how we’ve
been building heads ever since!
A few years ago one of these extremely rare offset
halfstacks came back into my possession and I
immediately placed it in the Marshall Museum at our
headquarters in Milton Keynes, England. Since then, all
who have seen and heard it have commented most
favourably - not only on its unique looks but also on its
rich, fierce, majestic tone.
To celebrate the dawn of a new century I wanted to
offer something truly special - hence this reissue. To
make this unique product as authentic as possible, we
have sought out and reproduced all of the original
components and methods of construction we used back
in 1962. From the hand-wired tag-board circuit housed
in an aluminium chassis, through to the original silver
Celestion Alnico loudspeakers. We have even
resurrected the original ‘coffin’ logo!
I sincerely hope that this eye-catching reissue of one
of the first Marshall amplifiers ever made, will provide
you with countless hours of playing pleasure. I'm sure
it will. I'm also sure it will prove to be a quite a
conversation piece too!
WARNING!
Please read the following list carefully.
A. ALWAYS use the correct power cord
B. NEVER attempt to by-pass the fuses or fit ones of the incorrect value.
C. NEVER attempt to replace fuses or valves with the amplifier connected to the mains.
D. DO NOT attempt to remove the amplifier chassis, there are no user serviceable parts.
E. ALWAYS have this equipment serviced or repaired by competent qualified personnel.
F. NEVER use an amplifier in damp or wet conditions.
G. DO NOT switch the amplifier on without the loudspeaker connected.
H. ENSURE that any extension cabinets used are of the correct impedance.
I. PLEASE read this instruction manual carefully before switching on.
WARNING : This apparatus must be earthed!
WARNING : Do not obstruct ventilation grille and always ensure free movement of air around the amplifier !
KEEP THESE INSTRUCTIONS
Introduction
As Jim has already stated, our goal, when building this limited edition, offset reissue, was simple. To make it as
close to the original as humanly possible! To this end we have gone to great lengths to recreate every single aspect
and specification of this visually and aurally striking item-from sourcing an exact replica of the original coffin logo (so
called because it was first made for us by a coffin manufacturer!), to ensuring that the output and power transformers
boast the same exact core lamination materials as they did back in 1962. Likewise, the amplifier circuit itself is hand-
wired on a hand-built tagboard, the chassis is constructed from aluminium and the valve complement is 3 x ECC83s
in the preamp, a GZ34 rectifier and a pair of KT66s in the power amp - just like the original.
We are delighted to report that many of our suppliers went to the same exacting lengths as we did when providing
us with parts for this reissue, and none-more-so than Celestion. Thanks to their commitment to this project they
successfully recreated the Alnico magnet, silver G12, model T0652 loudspeakers found in our museum piece-right
the way down to matching the same exact colours and lettering fonts used on the original label!
As is the case with all our amplifiers, the best way for you to truly appreciate this remarkable reissue is to grab
your favourite guitar, plug it in and play. Enjoy!
JTM45 O/S Front and Rear Panel Features
Front Panel Functions
The JTM45 O/S features four inputs, two per channel. The first channel is voiced for a high treble response with the
second channel voiced for normal response. The first input of each channel has more gain than the second input of
each channel and hence is louder. Though the first input of the first channel is the input that most guitarists use,
don’t hesitate to experiment. Some guitar players prefer to mix
the two channels by putting a patch lead between the second
input of channel 1 and the first input of channel 2 and then plug
their guitar into the first input of channel 1. Doing this allows
you to mix the different tonal characters of each channel for
greater flexibility.
See Diagram right.
Front Panel Functions
1. Power Switch
On / Off Switch for mains power to the amplifier.
2. Standby Switch
Controls H.T. or high voltage to the valves to allow
them to attain correct working temperature before
playing. To prolong the life of the valves it is
always advisable to switch on the Mains Power
Switch (item 1) about 2 minutes before switching
on the Standby (item 2).
On switching off, the Standby should always be
switched before the Power Switch.
The standby facility is particularly useful live
between sets and before playing, as it allows you to
keep the valves operating at a functional
temperature but without any sound being
produced.
3. Presence Control
Adds higher frequencies to the guitar tone, creating
crispness and bite. Turning this up will make the
sound more cutting and further forward.
4. Bass Control
Controls the amount of low frequencies or bottom
end in your tone.
5. Middle Control
Dictates the middle register of the amplifier.
Turning this up will make your guitar sound fatter.
Conversely reducing the amount of middle in your
tone will result in a sharper and thinner guitar
sound for the classic ‘scooped’ tone.
6. Treble Control
Controls the high frequencies of the guitar tone,
making your guitar sound brighter when increased.
7. Volume I
Controls the overall output level of channel 1.
Note - this channel is voiced for a higher treble
response than channel 2.
8. Volume II
Controls the overall output level of channel 2.
Note - channel 2 is voiced for normal response.
9. Input Jack
Connects the guitar to channel 1.
10.Input Jack
Connects the guitar to channel 1.
Note - this input has less gain than item 9.
11. Input Jack
Connects the guitar to channel 2.
12. Input Jack
Connects the guitar to channel 2.
Note - this input has less gain than item 11.
Rear Panel Functions
1/2. Loudspeaker Jacks
With all valve amplifiers it is imperative that the
amp is connected to a load whilst in operation and
that the impedance selected on the amp matches
the total impedance of the speaker cabinet(s) being
used. For example, if the amp is running into a
single 16 Ohm cab, the amp should accordingly be
set to 16 Ohms. If running into two 16 Ohm cabs,
the amp should be set to 8 Ohms. If running into
two 8 Ohm cabs the amp should be set to 4 Ohms.
Note - The matching cabinet supplied with this
amp is wired for 16 Ohms.
Failure to comply with these points will result in
damage to the amplifier.
3. Output Selector
Matches amplifier output transformer impedance
to loudspeaker load impedance.
4. H.T. Fuse
See label for correct value.
5. Mains Input
Connects unit to power supply.
6. Mains fuse
See label for correct value.
JTM45 O/S Front and Rear Panel Features (continued)
JTM45 O/S Front Panel
12
10871 2 6543
11
9
JTM45 O/S Rear Panel
6
5
43
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1
Whilst the information contained herein is correct at the time of publication; due to our constant improvement and development, Marshall
Amplification plc reserve the right to alter specifications without prior notice.
Marshall Amplification plc
Denbigh Road, Bletchley,
Milton Keynes, MK1 1DQ
England
Tel: (01908) 375411
Fax: (01908) 376118
Whilst the information contained herein is correct at the time of publication; due to our constant improvement and development, Marshall
Amplification plc reserve the right to alter specifications without prior notice.
BOOK-00057-00
Marshall Amplification plc
Denbigh Road, Bletchley,
Milton Keynes, MK1 1DQ
England
Tel: (01908) 375411
Fax: (01908) 376118
BOOK-00057-00
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2
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