Marshall 1974X
Marshall 1974X Overview:
Tone and Tech Talk The 1974X is an all-valve, 18 Watt, two-channel,
1x12" combo with valve driven tremolo and no
negative feedback in its cathode-biased output
stage. When building this handwired re-issue our
goal was both obvious and simple: to make it as
close as possible to the original.
As Jim has already pointed out, we went to
incredible lengths to achieve maximum
authenticity in terms of components, circuitry,
constructional methods, materials,
specifications, aesthetics, signal path, performance,
tonal characteristics and feel. We are delighted to report that our suppliers were equally as exacting in their
tasks – none more so than Dagnall Transformers and Celestion Speakers.
As you can see from its top panel layout, the 1974X is an extremely straightforward amplifier. Channel 1 (the
non-tremolo channel) only boasts two, self-explanatory controls: Volume and Tone; while Channel 2, the
Tremolo Channel, boasts four – namely Volume and Tone, plus Speed and Intensity for the valve driven
tremolo circuit.
Like all Marshall valve amplifiers, the 1974X sounds truly majestic when turned up full – and because of its
relatively low wattage this can be done at ear friendly volumes, making it a wonderful recording tool. In
keeping with bigger, non-master-volume, all-valve, Marshall amplifiers such as the 1962 'Bluesbreaker'
combo and the legendary 100 Watt 'Plexi' head, the 1974X's sweetly distorted, harmonically rich, thick,
musical tones result from the power valves being overdriven. Our proprietary, re-issued and 'aged' 20 Watt
Celestion speaker contributes to the combo's unique, punchy yet smooth sound as well. As a result, when
'cranked' the 1974X is incredibly touch-sensitive, cleaning up or, if desired, sitting right on the edge of
distortion when the guitar's volume is turned down. It responds well to picking dynamics too, 'sagging' nicely
when you play like you really mean it and, once again, cleaning up as you pull back on your picking attack.
There now follows some information regarding the inner workings and build of the 1974X.
Valve complement: Three ECC83s (12AX7s) in the pre-amp, a EZ81 rectifier and a pair of EL84
power valves working in push-pull. All valves are of the highest quality available and go through a meticulous
grading and testing process.
The way the three ECC83s (V1, V2 & V3) in the pre-amp are utilised is as follows:
V1 is dedicated to Channel 1, the non-tremolo channel. As Channel 1's pre-amp has a single gain stage,
each half of the valve (the ECC83 being a dual-triode) acts as a dedicated gain stage for the channel's two
inputs (which are identical). V2 acts as the amplifier's phase-splitter. V3 is dedicated to Channel 2, the
Tremolo channel. To be precise, one half of the ECC83 acts as the single pre-amp gain stage for the
channel's two inputs (High and Low) while the other half acts as the oscillator for the amp's tremolo circuit.
Due to the fact that the EZ81 rectifier valve and also the pair of EL84 output valves attain extremely high
temperatures when the amplifier is in use, their bases are made from the highest grade ceramic available.
Marshall 1974X Top Panel Features:
1. INDICATOR
This filament bulb indicator will light up when your
amplifier is switched on. It will not be lit when the
amplifier is switched off and/or is not receiving
mains power.
2. STANDBY SWITCH
The Standby Switch is used in conjunction with the
Power Switch (item 3) 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 application of the voltage
required to heat the valves to their correct
operating temperature – hence the switch's name.
After approximately two minutes the valves will
have reached the correct operating temperature
and the Standby Switch can be engaged. Upon
doing this the H.T. (High Tension) voltage required
by the two EL84 output valves to pass signal (and
hence produce sound) is applied.
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,
upon full power down, always disengage the
Standby Switch prior to the main Power Switch.
3. 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.
CHANNEL 2 THE TREMOLO CHANNEL
4. TREMOLO SPEED CONTROL
This controls the speed of tremolo oscillation when
this effect (which can be switched on/off via the
supplied footswitch) is being used. Oscillation
speed increases when the Speed control is turned
clockwise and decreases when it is turned
anticlockwise.
5. TREMOLO INTENSITY CONTROL
This controls the intensity or depth of the tremolo
oscillation when the effect is being used. The effect
depth increases when the Intensity control is turned
clockwise and decreases when it is turned
anticlockwise.
6. TONE CONTROL
This adjusts the tonal character of the Tremolo
Channel. Turning this control clockwise increases
the amount of high frequencies (treble) present in
the sound.
7. VOLUME CONTROL
This controls the volume of the Tremolo Channel.
Turning it clockwise increases the volume level of
the channel.
8. CHANNEL 2 INPUTS
These are the guitar inputs for the Tremolo
Channel. The top one is the 'high sensitivity' input
for this channel, the bottom one is the 'low
sensitivity' input which is 6dB lower (i.e. half) than
the 'high sensitivity' input and has a darker sound.
Always use a high quality screened guitar lead.
CHANNEL 1THE NON-TREMOLO CHANNEL
9. TONE CONTROL
This controls the tonal character of Channel 1.
Turning the tone control clockwise increases the
amount of high frequencies (treble) present in the
sound.
10. VOLUME CONTROL
This controls the volume of Channel 1. Turning it
clockwise increases the volume level of the
channel.
11. CHANNEL 1 INPUTS
These are the guitar inputs for this Channel and
both are identical.
Marshall 1974X Rear Panel Features:
1. TREMOLO FOOTSWITCH JACK
This is where the supplied Tremolo on/off
footswitch is plugged in.
.
2. LOUDSPEAKER OUTPUTS
There are two parallel loudspeaker output jacks
provided for connection to the internal speaker
and/or an external load, i.e. speaker extension
cabinet(s). When connecting speaker(s) please
always ensure that the amplifier's output
impedance is set correctly (item 3).
WARNING! Never use the combo without a load
attached!
Always use a non-screened Marshall approved
speaker lead when connecting an extension
cabinet to these units.
3. OUTPUT IMPEDANCE SELECTOR
Matches the amplifier's output to the load (speaker)
impedance.
As is the case with any Marshall all-valve amplifier
it is imperative that: a) the amplifier is connected to
a load whilst in operation and b) the impedance
selected on the amplifier matches the total
impedance of the internal speaker and/or extension
speaker cabinets.
The combo's internal speaker is 15 Ohms so when
it is being used by itself the Impedance Selector
must be set to 16 Ohms. If an additional 16 Ohm
extension speaker cabinet is used in conjunction
with the internal speaker the Impedance Selector
should be set to 8 Ohms.
WARNING! An extension speaker cabinet with an
impedance of less than 16 Ohms should NOT be
used in conjunction with the internal speaker.
The amp should be completely powered down
before the Output Impedance Selector is turned.
Failure to comply with any of the points raised in
this section will result in damage to the amplifier.
4. MAINS FUSE
The correct value of mains fuse is specified on the
rear panel of the amplifier. NEVER attempt to
bypass the fuse or fit one of the incorrect value.
5. H.T. FUSE
The correct value of H.T. fuse is specified on the
rear panel of the amplifier. NEVER attempt to
bypass the fuse or fit one of the incorrect value.
6. MAINS INPUT
Your amp is provided with a detachable mains
(power) lead, which is connected here. The specific
mains input voltage rating that your amplifier has
been built for is shown on the back panel. Before
connecting for the first time, please ensure that
your amplifier is compatible with your electricity
supply. If you have any doubt, please get advice
from a qualified technician. Your Marshall dealer
will help you in this respect.
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