Marshall Amplification 1974X Owner's Manual

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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.

Important Note: In order to comply with the strict safety requirements of modern legislation, the 1974X’s
valves have been housed in a removable, vented aluminium cage. This is obviously a deviation from the
original spec. but has no tonal or performance impact on the amplifier what-so-ever.

Introduction

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Output Transformer:In the original 1974 the speaker was hardwired directly to the 8 Ohm tap on the

transformer. To make the re-issue more user-friendly, the internal speaker is not hardwired to the
transformer – instead the speaker cable is fitted with a jack and then connected to the amp via one of the
two speaker outputs on the rear panel of the combo. The rear panel also boasts an impedance selector with
three options – 4, 8 or 16 Ohms.* These additions (the original didn’t have speaker outputs or an impedance
selector) give the user maximum flexibility, enabling you to use an external cabinet (Note: the 1974CX, a
cosmetically matching 1x12" extension cabinet loaded with the same 20 Watt Celestion speaker, is
available) in conjunction with the internal speaker or, if you wish, disconnecting the internal speaker and
using the 1974X to drive one or two external speakers cabs.

*Note 1: Adding speaker outputs and the impedance selector has no effect on the tonal authenticity of the
1974X, they merely add to its potential flexibility.

*Note 2: On the original output transformer you could choose from one of three taps: 8 Ohms, 16 Ohms and
something called a ‘100 Volt line load’ – a quaint offering that’s completely irrelevant to musical applications.
So, we replaced it with a 4 Ohm tap instead – a far more useful option, the addition of which has no effect
what-so-ever on the performance of the transformer.

Mains (Power) Transformer:Just like the ‘off-the-shelf’ device used in the original, the re-issue’s

mains transformer is a ‘drop through, half-shroud’ type. In order to comply with strict, current-day safety
legislation the custom-manufactured Dagnall transformer we’re using is physically larger than the one in the
original but, as with the output transformer, we went to great lengths to ensure that its performance mirrors
that of the original. We paid particular attention to exactly replicating an effect called ‘regulation’ – which is
the way that the voltage from the transformer that feeds the valve circuitry varies according to the power
delivered in the speaker.

Chassis: As in the original, the chassis we’re using is made from aluminium. While the original chassis

was open-ended though, the re-issue’s is closed-ended. This has been done purely for
strength/constructional integrity reasons (all the open-ended originals we’ve seen have been quite badly
deformed) and has no sonic effect (positive or negative).

Speaker: A definite contributing factor in the sound of the vintage 1974 amplifiers is the way the

Celestion Greenback loudspeaker sound softens with age. In order to establish exactly the sound we were
trying to recreate we listened to many vintage correct Greenbacks from our Museum here in Bletchley. We
then met up with Celestion to decide a strategy to recreate the gorgeously smooth tones of our vintage
Greenbacks which are over 35 years old.

Celestion revisited the 1967 recipe for the original 20 Watt, ceramic magnet, 15 Ohm, Greenback T1221
speaker used in the 1974 and supply it to us exclusively. They meticulously duplicated every critical vintage
parameter from winding lengths, coil former dimensions and edge treatment to using the original dustcap
material and adhesive. In sound tests these speakers were close, but still lacked something of the sonic
signature of the originals.

Further investigation uncovered that the magnetic
properties and cone make-up of the vintage speakers
varied slightly from the newly manufactured speakers.
This slight sonic discrepancy led us to investigate the
possibilities of somehow ‘ageing’ the speakers.
Celestion’s proprietary ‘ageing’ is largely achieved by
the following two things:
i) Matching the magnetic flux to that of our vintage
references in order to duplicate the output of the older
speakers. Doing this not only affected the ‘loudness’
of the speakers but also altered the tonal balance,
warming up the low end and also making the top end
less aggressive – exactly like the originals.
ii) Specially manufacturing the cone material to be
more ‘pulpy’, recreating the ageing effect and thus
further softening the sound of the combo.

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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 1

THE 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.

1974X Top Panel

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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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1974X Rear Panel

Follow all instructions and heed all warnings

KEEP THESE INSTRUCTIONS !