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5
1. POWER SWITCH
This is the On/Off switch for mains power to the
amplifier.
Note: Please ensure the amplifier is switched off and
unplugged from the mains electricity supply whenever it
is moved.
2. STANDBY SWITCH
The Standby Switch is used in conjunction with the
Power Switch (item 1) to 'warm up' the amplifier before
use and to prolong the life of the output valves.
When powering up the amplifier always engage the
Power Switch first,leaving the Standby switch on
'Standby'.This allows the heater voltage to bring the
valves to their correct operating temperature. After
approximately two minutes the valves will have reached
their correct operating temperature and the Standby
Switch can be engaged,enabling the HT without
'shocking' cold valves.
In order to prolong valve life,the Standby Switch alone
should also be used to turn the amplifier on and off
during breaks in a performance. Also,when switching
off,always disengage the Standby Switch prior to the
main Power Switch.
3. INDICATOR
This 6.3 Volt incandescent filament indicator will light up
when your amplifier’s heaters are energised at mains
power switch on,(irrespective of standby switch
position).It will not be lit when the amplifier is switched
off and/or is not receiving mains power.
4. PRESENCE CONTROL
This control operates in the JTM45/100's power section
and adds high frequencies to your sound by altering the
power amplifier's negative feedback.Turning this control
clockwise adds more 'sparkle' to your sound,making it
crisper and more cutting.
5. BASS CONTROL
This adjusts the bottom end,turning it clockwise
increases the amount of low frequencies in the sound.
6. MIDDLE CONTROL
This adjusts the level of those all-important mid-range
frequencies.Turning it clockwise increases the mids and
fattens your sound,giving it more punch.Turning it
anticlockwise reduces the mids,producing a more
'scooped' tone.
7.TREBLE CONTROL
This adjusts the top-end.Turning it clockwise increases
the amount of high frequencies present in the sound,
giving your guitar tone a brighter edge.
Note: The following four controls - PRESENCE (item
4),BASS (item 5),MIDDLE (item 6) & TREBLE (item 7)
- are all shared,meaning that they are common to both
Channel I and Channel II.They are highly interactive and
altering one control can change the way the others
behave.For this reason,experimentation is
recommended.
8. LOUDNESS 1
This controls the overall output level of Channel I,
turning it clockwise increases the volume.This channel
is voiced for a higher treble response than Channel II,
hence its 'High Treble' labelling.
9. LOUDNESS II
This controls the overall output level of Channel II,
turning it clockwise increases the volume level.This
channel is voiced for a 'normal',flatter response and is
labelled as the 'Normal' channel.
10. HIGH SENSITIVITY INPUT FOR
CHANNEL I
This is the 'high sensitivity' guitar input for Channel I,the
so called High Treble channel.It is the most commonly
used input.Always use a high quality screened guitar
lead.
11. LOW SENSITIVITY INPUT FOR
CHANNEL I
This is the 'low sensitivity' guitar input for Channel I.
12. HIGH SENSITIVITY INPUT FOR
CHANNEL II
This is the 'high sensitivity' guitar input for Channel II,
the so called 'Normal' channel.
13. LOW SENSITIVITY INPUT FOR
CHANNEL II
This is the 'lo
w sensitivity' guitar input f
or Channel II.
Interesting aside: Back in the day,a 'high sensitivity'
input jack was recommended for use with a guitar
loaded with low-output pickups (e.g.:single coils) while
4
Tone Circuit: In typical Marshall fashion,the JTM45/100’s shared tone network is passive and interactive.By
interactive we simply mean that the settings of the Bass and Treble controls affect the amount of mid-dip (cut)
available via the Middle control.
Tag Boards: The tag boards used in your hand wired re-issue are exactly the same as those in the original in terms
of thickness and matrix pitch.The material we're using is made exclusively for us and is ‘UL recognised Micom type
Marshall EM42’.The reason we didn’t use a board with the exact same chemical composition as in the original units is
because that material doesn't pass current safety requirements regarding flammability.
Transformers: The mains (power) and output transformers are vital to the performance,sound and feel of an all-
valve amplifier.Because of this we spent a great deal of time studying and analysing the constructional methods and
materials used in the original transformers so we could match everything as closely as possible.We also went to great
lengths to ensure that the all-important electrical characteristics and performance of the originals were duplicated
exactly.In order to achieve these vitally important goals we worked extremely closely with our associates in the R&D
department of Drake – the company which supplied us with the output transformers used in the original JTM45/100.
Mains (Power) Transformer: In the original JTM45/100 the mains transformer was an “off-the-shelf” device
purchased from a highly regarded general electronic components supplier.Referred to as the “RS De Luxe ”this
transformer is no longer available,but with the help of Drake’s expertise we were able to replicate the performance
of the original “De Luxe” of which we have several genuine examples.We paid particular attention to an important
electrical effect called ‘regulation’ which is the variation in behaviour of the HT voltage and current from the
transformer and is dependant on load demand (i.e.how loud you’re playing!).This behaviour affects how the amplifier
compresses and reacts to saturation when played at high volumes – hence its importance.
Output Transformers: As already mentioned,the pair of output transformers used in the original JTM45/100s were
supplied by Drake,as are those in your reissue.Fortunately Drake still had their original documentation intact after all
of these years,a factor which obviously helped ensure that the reissues are 100% accurate.
Power Supply: This circuit has the same exact filtering on the H.T.(high voltage DC,a.k.a.the B+ voltage) line as the
original versions,a factor that contributes to the JTM45/100 having a unique,dynamic characteristic all of its own.
Chassis: We are using a box-section chassis made from 16-gauge mild steel with butt-welded corner joints.The steel
is also passivated giving lifelong resistance to corrosion.
Front Panel: Extra thick,gold coloured Plexiglas (actually Perspex,causing some people to refer to it as ‘Perplexi’!),
exactly as the original.Specific details pertaining to the front panel features can be found on page 5 of this manual.
Rear Panel: Made from cream styrene with gold print,just like the original references.
Head Cabinet Construction: High-grade,flawless (knot-free) Baltic birch-ply with finger locked joints for maximum
strength.The main cabinet frame (sides,top and bottom) are 15mm ply,the front baffle is constructed from 12mm ply
while the back of the cabinet is 9mm ply.All edges have a 15mm radius.
Head Cabinet Cosmetics: The Marshall Block logo,black Levant covering,original venting,beading and piping
duplicate the look and style of the originals.
ENGLISH
ENGLISH
Front panel features
1 2 3 4 5 6 7 8 9 11 13
1210
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