MARSHALL AVT412A Marshall_Tips
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Marshall - Impedance Settings
Essentially in any Marshall set-up there are only three possible choices of impedance, 4 Ohms, 8 Ohms or 16 Ohms. If you are using a single cabinet then it is pretty obvious that the amp should be set to the same impedance as that of the cabinet i.e. 4 Ohms for a 4 Ohm cabinet, 8 Ohms for an 8 Ohm cabinet etc.
If you are using two cabinets of the same impedance, you divide the impedance of one cabinet by the number of cabinets being used. So for two 8 Ohm cabinets you would set the amp to 4 Ohms, or for two 16 Ohm cabinets you would set the amp to 8 Ohms.
In situations where you are using cabinets of different impedance's the most likely configuration would be one 16 Ohm cabinet and one 8 Ohm cabinet, in which case you would set the amp to 4 Ohms. As a rule of thumb if you work on the idea that where using two cabinets of different impedance's you set the amp to half the value of the cabinet used with the lowest impedance, then you won't go far wrong. There really is no mystery to any of the set-ups described above, but it is vital to the correct and safe working of any amplifier to always ensure that the impedance is correctly matched
Sound Settings
As sound is such a subjective thing and there are so many variables involved, from the weight of your guitar strings through to the type of guitar and strength of pick-ups etc. it is very difficult to give serious advice. Generally if you start with everything at 12 o'clock and adjust from there, then let your own ears do the rest. Obviously, the more you increase the gain, the more intense the distortion becomes. Another important thing to remember is that, particularly on valve amps, the EQ is inter-active so adjusting one control can affect the others in relation. The best thing really is to experiment and don't be afraid of being radical as there is no absolutely right or wrong way to set up a sound. If it sounds good then use it.
Top Ten Tips
Here are the answers to the most commonly asked Marshall service questions. If you follow these simple guidelines you will ensure that you get the longest possible life from your valves (tubes) and maximum performance from your Marshall.
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With any valve (tube) amplifier always switch on the mains switch two minutes before switching on the Standby.
This allows the valves (tubes) to reach their full working temperature before use.
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When replacing output valves (tubes) always replace the whole set, preferably with valves (tubes) of the same make.
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Never mix valve (tube) types. So if your amplifier has EL34 power valves (tubes) you must always replace them with EL34s. If it has 5881 or 6L6 valves you must use those.
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Always make sure that the pins on the base of the valve (tube) line up exactly and fit the valve base on the amplifier perfectly.
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If possible always allow the amp to cool down before moving it.
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Always use high quality guitar and speaker leads and check them regularly.
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Never store your amp in damp or overly humid conditions. Garden sheds, greenhouses or garages - not a good idea.
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Always ensure that any cabinets used have sufficient capacity to handle the full power of your amplifier (bearing in mind that an amplifier can give peaks far in excess of its normal rated Wattage).
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Always make sure that the amplifier has the correct impedance selected to match the cabinets being used.
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Always have your amplifier serviced by a qualified technician.
MARSHALL AVT412A History
MARSHALL EXPLOSION
By the end of 1965 a production of 40 amplifiers and 100 cabinets per week was unable to reduce the growing back orders. Demand, fuelled by the appointment of a distribution company, exploded. The world was crying out for more Marshall. The solution was another move. Marshall now moved to Bletchley, Buckinghamshire into 7000 sq.ft. Export sales grew as the success of British bands spread abroad. Throughout the 1960's Marshall sound powered the most influential and original guitar players. From Pete Townshend with The Who, Eric Clapton with his distinctive Bluesbreaker tone, then with Cream; to Ritchie Blackmore with Deep Purple and the greatest ambassador of all, Jimi Hendrix. With his prodigious guitar talent, he used the power of Marshall as a creative tool and as an extension to the instrument itself. 1968 and the sales explosion created the ned for greater capacity. A 14000 sq.ft. purpose built factory was opened and at last the world market stood a chance of fulfilment. Investment in massive PA systems powered the tours of many early 70's “super groups”. Multi coloured Marshalls appeared and the product range expanded.
THE MASTER VOLUME
By 1975 the first transistor heads were introduced, followed by the first Master Volumes in 1976. Guitar styles soon adapted to squeeze the most from this extension of the Marshall sound. Here began the quest for gain which continues to this day.
A DOUBLE LANDMARK
1981 saw the end of the 15 year distribution contract and the introduction of the JCM 800 Series. We were now fully back in control of our own destiny, with phenomenal products, another demand explosion occurred. The long awaited Split Channel amplifier came in 1982 and was an instant success, with it's incredible flexibility and distortion control; the world loved it!
THE QUEENS AWARD
One of the proudest moments for Jim and the company came in 1984 with the presentation of the Queens Award for Export Achievement. This was followed by the move to our present site, where a staff of 90 now occupied 50000 sq.ft. Another personal triumph for Jim was his induction into the Hollywood Guitar Centre Walk of Rock in 1985.
SILVER JUBILEE
Celebrations of the Marshall 25th Anniversary and Jim Marshall's 50 years in music, reverberated throughout the world in 1987, Special Limited Edition Jubilee products received great acclaim and continued our upward spiral.
A FIRST CLASS TEAM
As the company has grown, Jim has assembled a first class team, which in the lead up to the 90's has taken Marshall to new heights. The factory has now extended to 70000 sq.ft. and the workforce has grown to 220. The present generation of ever more demanding guitar players are enjoying our recent innovations. The Series 9000, JCM 900 valve amps, SE1OO speaker emulator, Valvestate and new effects pedals, have all received the welcome we appreciate most, they are being PLAYED.
1992 AND BEYOND
To celebrate our 3Oth Anniversary we have produced a remarkable new amplifier which holds true to the tradition of excellence instilled in the company by its founder. One man's drive and vision has created this legend which continues to grow.
The history of Marshall amplifiers has become a source of great fascination and interest over three decades. In 30 years of manufacturing we have made a vast number of different models using many materials and techniques.
Documentation from those early years is virtually non-existent. The pressure to build amplifiers was so great that detailed record keeping was impossible. This pressure also created anomalies in the products themselves as component and minor cosmetic changes could be phased in at any time where supplies ran out but production had to continue.
The following information is a rough guide to the major changes in the most popular Marshall models since 1962.
1962 - The original production of those first JTM45 models featured the following:- Serial numbers starting at 1004; Smooth black covering: White grill cloth: Silver polished aluminium panels: No rear panel: Rectangular metal logo with red block lettering: Leather handle: Single speaker output: 5881 or 6L6 valves. Cabinets - Straight fronted, using the same logo and fret cloth: Celestion G12 15 speakers.
1963 - Production essentially the same as the above but with the following changes:- Twin speaker outputs: Black knobs with serrated edges: Changed to white engraved panels late in 63: First angled cabinets, similar finish and speakers to the straights but taller than today's 4x12.
1964 - Serial numbers begin with 2: Valves now changed to KT66's: Logo changed to gold plastic with black lettering mid year: The first combos made late 64: Speakers now changed to G12 20's.
1965 - Panel changed to gold plexi glass: Serial numbers no longer reliable: Handles changed to plastic with larger end cap: The first 100 Watt amps appeared in larger cabinets with two 50 Watt transformers, JTM45 panels, KT 66 valves and without GZ34 rectifier. The first serious combo production of models 1961 4x10 and 1962 2x12 took place. The same features as the JTM45 but with the addition of tremolo. Fret cloth changed to green flecked weave late 65. The 'stack' was born from Pete Townshend's original request for an 8x12 cabinet. Late 1965 saw the change to green fret cloth
1966 - TheJTM45 changed to JTM50 on panels: Block logos now changed to white script with gold coloured plating: Valves changed to EL34's and Gz34 rectifier phased out: Transformer uprated. 100 Watt production was now standardised with a single 100 Watt transformer and EL34 output valves. The 1961 and 1962 were upgraded in line with the heads and cabinets slimmed down. All cabinets now had corner locked joints. As a method of quality control all cabinets were signed inside.
1967 - Chassis were all upgraded from aluminium to steel construction. The first 200 Watt Majors appeared, with just treble, bass and volume controls, “active” tone circuitry and KT 88 valves. 10 and 18 Watt combos introduced in 1x12, 2x10, 2x12 tremolo or non tremolo versions. Fret cloth on cabinets changed to basket weave in late '67.
1968 - The Major was modified to match the normal panel layout and active electronics dropped. Gold logos changed to white.
1969 - New gold metal panels were introduced across all ranges. Serial numbers now followed a dating system with the letter A appearing after the number. By 1970 cabinets had all changed to check fret cloth. From this point onwards, Marshall amplifier history is much more easily accessible from the serial number and the inspection tag attached to every amp chassis.
Notable dates after 1970 are as follows:
1970 - The period of coloured Marshalls. Orange, purple, blue etc.
1974 - The first transistor 100 Watt amp (model 2098) was introduced.
1975 - Design of the first Master Volume amp was completed. 1976 - All units changed to thicker wood finish and large white script logos. Black fret cloth gradually introduced.
1981 - JCM 800 range launched.
1982 - The first split channel amps arrived.
1987 - 25/50 silver Jubilee units produced. 1989 - Series 9000 rack systems released.
1990 - The year of JCM900.
1991 - Valvestate swept the world.
1992 - The 30th Anniversary.
With each passing year more Marshall amplifiers achieve “classic” status. The Anniversary Series Limited Edition amplifier is such a fine piece of engineering and technology, that it will achieve this status instantly.
One thing is certain, whichever Marshall you own it has a unique pedigree and at some time will command its own place among the Marshall classics.
Marshall AVT412A 200 Watt 4x12 Cab
