Manual Marshall 1974X (page 3 of 5) (English)

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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.

ENGLISH

Tone Circuit: In typical Marshall fashion, the tone network is post gain and passive. The tone circuit

involves a blend of high frequency pre-emphasis and passive high frequency cut – the mix of which is

dependant upon the setting of the Tone control on the channel being used.

Components: With the obvious exception of the valves, all components used were sourced from

European and American manufacturers – including some custom built, ‘double can’ (a.k.a. ‘dual gang can’ or

‘dual electrolytic’ – meaning two capacitors in a common case) power supply capacitors due to the odd value

used in the original – one of many steps taken to ensure maximum authenticity.

Tag Board: This is exactly the same as the original in terms of dimensions, thickness and matrix pitch.

The material used is 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 legislation regarding flammability.

Transformers: Because the 1974 combo was produced relatively early in Marshall’s history (1966 - ’68),

Jim had yet to strike up his now well-known relationship with transformer manufacturers, Dagnall and Drake.

As a result, both the power and mains transformers used in the original 1974s were ‘off-the-shelf’ devices

purchased from a highly regarded, general electronic component supplier. This company, whilst still in

existence, does not have records of exactly who manufactured the original transformers.

As you probably know, the output and mains transformers are vital components in an amplifier as they

influence performance, sound and feel. Consequently, we worked extremely closely with our associates in

Dagnall’s R&D department in order to duplicate the original transformers in all areas. To do this we spent a

great deal of time and attention studying and analysing the constructional methods and materials

(e.g.: lamination grade, insulation, coil spacing, etc.), used in both transformers so we could match

everything as closely as possible and also ensure that the all-important electrical characteristics and

performance were identical. With Dagnall’s expert help and dedication, we’ve done exactly that.

ENGLISH

OUTPUT

TRANSFORMER

EL84 OUTPUT

VALVES

V3 V2 V1

MAINS

TRANSFORMER

ECC83 VALVES

EZ81

RECTIFIER VALVE

1974X hbk 21/5/04 3:52 pm Page 2

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Marshall 1974X Manual

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