Marshal JCM 800

 

Pierre Schwartz

 

 

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Marshall JCM 800 model 2210

The amp model is from 1989, its a 50watt (2 x el54 tubes for output, 6 RCA A12 pre amp tubes)

Serial number is X22917

 

Very large sice pic of the inside of the JCM 800

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Schematic diagram of JCM 800 Lead

For the past two decades, one name has been synonymous with the best in rock amplification. Marshall has now become a household name throughout the world as a symbol of precision acoustic engineering, to be relied on, not only for superlative sound quality, but for high performance night after night.

Each amplifier chassis is constructed from a minimum of 16 S.W.G. steel, precision cut, punched, bent and seam-welded to form a substantial, rigid foundation strong enough to take all the knocks of the road. Industrial grade cadmium passivating ensures many years of rust-free operation.

All electronic components are selected and tested to out perform their required functions, and the electrical hardware, such as switches, selectors, etc., comply to most international safety standards to ensure the user is safe from the risk of electric shock. The same applies to both the mains and output transformer, that are designed and built to withstand full output for hour upon hour. To complete the electrical specification all valves are selected from the finest grades available. Once assembled and wired, using both hand and machine techniques, each chassis is fully tested by the team of electronic engineers.

After testing and adjusting, each chassis is assembled into cabinets that are manufactured to an equal standard as the chassis. Each cabinet is made from finest quality birch ply, corner locked and r.f. bonded for immense strength and longevity. After the protective and decorative RV.C. covering is bonded and stretched onto the cabinet, A.B.S. corner protectors and air vents are riveted in position, and the heavy-duty strap handle and shock absorbing feet are screwed on.

A process of constant development work and a keen awareness of the requirements of the market piece, have resulted in the design and manufacture of a number of new amplifiers, beginning with the now famous 2000,2001 professional series. The success of these models, with their twin channel formats and versatile facilities, led in turn, to the production of the equally successful 5Ow Combo model 4210. To complete this line of development, two new heads have been produced which, although based closely on the Combo 4210, have been modified to accommodate the requirements of high powered stage loudspeaker stacks.

The preamplifier section has a single input, which is then split between the normal channel and the boost channel, these are footswitch selectable, hence the terminology “Split Channel”. The normal' channel has volume, treble and bass controls, offering a wide range of sounds and is aimed at being the clean or rhythm channel. The 'boost' channel has an L.E.D. indicator to show selection and features gain, volume, treble, middle and bass controls. This is aimed at being the 'dirty' or lead channel and, as such, offers the player the facility of long, controllable sustain with the sound quality that has made Marshall the big name in guitar amplification.

Both channels are fed into the 'master' section that contains the footswitch-controlled Hammond reverb, presence control, effects send and return sockets, and the 'master volume' control that adjusts the apparent output power of the amplifier.

The output stage of each amplifier features either 50 watts or 100 watts of Marshall power and contains the usual Marshall items of selectable mains voltage and output impedance, fuse-holders etc., enabling the amplifier to be used world-wide with almost any loudspeaker configuration. Also on the output stage, is a frequency compensated D.I. socket and volume control to facilitate the ease of slaving or recording, yet maintaining the sound quality projected by Marshall loudspeaker systems.

Although attaching great importance to its development programs, Marshall are not in the business of planned obsolescence, and are acutely aware of their reputation for longevity, in both product and model range. Thus, despite the success of recently developed equipment, the original Marshall amplifiers are still available and are as popular as ever. Below are descriptions and diagrams of these amplifiers.

These two amplifiers have undergone a major re-design programme to keep abreast of the requirements of modern bass playing trends. The amplifiers feature two mixable inputs with volume control, active treble and bass controls and a middle circuitry sweepable from 400 HZ to 1 KHZ, plus a slope control that filters the low fundamental notes for that tight punchy sound when playing loud. All this, plus an improvement of bass in the power amp, leads Marshall to believe that the 1992 is the finest 100 watt bass amplifier that they have ever produced.

This is the panel of the classic Marshall amps, so much favoured and featured by some of the world's greatest guitarists and bands. There are two models with this format:- model 1987 standard lead 50 watt, the original and legendary Marshall amplifier with its unique sweet overdriven valve sound and sustain, and model 1959 standard lead, with that incomparable 100 watt raunch. Both amps feature the same controls and twin channels, one channel is normal (input II) and the other has a high treble response. Each channel has its own volume control and is mixed into the tone network of treble, middle, bass and presence controls. Variable mains and output selectors enable both amps to be used around the world, with virtually any speaker system.

The amps were developed out of the original Marshall circuitry to enable the musician to reproduce the classic Marshall overdrive sound at any volume level. By varying the pre-amp volume, and master volume controls the sound can be varied from a clean crisp sound to a rich overdrive sound at a controllable volume. As with the standard amps, the master volume series have twin inputs, one having greatly increased gain. Both channels mix into the usual Marshall tone circuitry of treble, middle, bass and presence control. This is an exceedingly versatile amp, and perfect for the discerning guitarist.

(Source Marshallamps.com)

 

Marshall Amplifier Date Codes

The newest models are incredibly easy to date (read on, if you aren't already aware of the current serial numbering system) but dating older amps (pre-1993) are slightly more involved. Here's the story so far…  

July 1969 - September 1992  

In July of '69, Marshall introduced their first date code system. To determine the year of manufacture, a letter of the alphabet was included in the serial number. Here's how it works:

A – 1969/1970       C – 1971               D – 1972               E – 1973

F – 1974               G – 1975               H – 1976               J – 1977

K – 1978               L – 1979               M – 1980               N – 1981

P – 1982               R – 1983               S – 1984               T – 1985

U – 1986               V – 1987               W – 1988              X – 1989

Y – 1990               Z – 1991/1992

“B” was skipped because “A” ran for 18 months and “I,” “O” and “Q” were also skipped because they looked too similar to numbers.

As a rule, the serial number is usually located on the back panel of the chassis but some amplifiers made between 1979 - 1980 had them on the front panel. Now, at this point you're probably wondering where exactly this letter can be found within the serial number. That's a very good question so here's the answer. From July 1969 to December 1983, the letter was put after the serial number. For example, let's say you found this stamped on the back panel:

SL/A  14532  D

What does it mean?  

SL/A = model number

12532 = serial number

D = Date code (1972)

Tubes pre RCA 12AT6

12AT6, 12AT7 | Electronic Vacuum Tube Specifications

Tubes output

Groove tubes EL34 changed in 2005

Groove Tubes Power 4xGTEL34R Quartett www.thomann.de no. 3944048 82,90 EUR

This Russian made pentode is standard issue on many UK amps and has great durability, although as with most Russian power tubes the break up is a bit harsh and they lack high end as compared to the true European models.Unique sound, slightly edgy distortion when pushed hard. Newly exclusive GT design, close copy of classic Mullard type with good power and flat tonal response.  The most reliable of all in this family.

 

Pictures of my amp serial SL/A 10209

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Contact info: pierreschwartz@pierreschwartz.com