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Marshall Amp Frequently Asked Questions (FAQ)
This collection of Marshall Frequently Asked Questions (FAQ) is a work in progress. The links and information herein are subject to change, however the most current version is always available at: http://faq.marshallarts.org.
The biggest change involves preamp tubes. This is where the amplification process really starts, so a little change at this end of the signal chain makes a big difference. Some preamp tubes stay clean until they're really "pushed," which provides more headroom. Other ubes tend to break up sooner, giving a nice distorted sound at lower preamp volume levels. If you're into experimenting, we recommend our friends at The Tubestore, who have have a number of excellent online articles about the mechanics and sound differences among various types and brands of valves (tubes).
It may seem silly to put this in print, but make it a practice never to allow beverages, candles, paper clips, etc. to be placed on top of your amp. Especially if it's a tube amplifier that has top-mounted cooling ports. While not in use, a protective cover that's made for your amp offers additional protection for those times when the amp is out of your sight.
Note that running an amplifier at a higher output setting does put more wear on the power tubes. This is offset by the increased versatility of using the Powerbrake to control the amplifier tone at lower volume levels for recording, practicing, and live performance.
The owner's manual for the Powerbrake mentions that the PB-100 is built to handle 150 watts RMS. This is important, since a 100 watt Marshall tube amp delivers more than 100 watts. RMS power ratings are usually measured at no more than 1% distortion, which as we all know, is a lot less distortion than most of us play our Marshalls at! It's good to know that the PB-100 is designed to handle a full 100 watts of Marshall power.
For more information, see the Powerbrake page.
Using a Powerbrake on a MV amp allows power tube saturation to occur, resulting in the more pleasing, musical distortion preferred by recording artists and stage performers alike (but at a volume level that won't blow apart the diaphragm of that vintage RCA ribbon studio mic).
For more information, see the Powerbrake page.
Early Marshall models had dates stamped into the amp chassis. Later models have a date code sticker applied to the rear of the device. You can find more information by visiting the date finder page.
Heck no! Marshalls are known for delivering the "sound of rock" when the controls are "dimed" or set to 10. Marshall agrees, stating "[A]ll Marshall Products are designed to work at maximum but if you run your amplifier at maximum you can shorten the life of certain components such as valves, but it should not damage the actual unit."
Power tubes, especially, wear more heavily when operated at full volume. When the crispness and attack of your amp begins to degrade, it's probably time to buy a new set of tubes and replace them.
Marshall does not recommend the removal of any valves (tubes) as their 100 watt amplifiers are designed to work with four power valves. The removal of two can and will cause damage. One way to reduce the output of the amplifier is to use a power soak device, such as the PB-100 PowerBrake. This gives you a lower physical volume output, letting you turn up the amplifier volume controls to achieve the perfect tone you're after.
That depends. If you replace your amps existing tubes with the same brand and configuration, then generally speaking, the tone may not be that different. Reliability will be improved, however, especially if you replace your old, worn out power tubes with new ones.
The 12AX7 is the American model number for the ECC83 preamp valve. Marshall, being a British company, uses the British part number designations in their specification and part number designations.
The 5881 is the same type of valve as the 6L6, but with slightly higher output. The bias on the amplifier will need to be set depending whether you are using 5881 or 6L6 power tubes. For safety's sake, all work of this nature must be carried out by a qualified engineer, due to the high voltages present inside your tube amplifier.
When replacing power tubes to ensure they work correctly, give the required sound, and ensure a long working life, Marshall recommends the amplifier be re-biased. If the bias is not set correctly when the power valves are replaced, damage to the valves and amplifier will result. Biasing is not expensive, and can be performed by most reputable shops. Your power tubes -- and your amp -- will operate longer and safer with the proper bias adjustment. For safety's sake, all work of this nature must be carried out by a qualified engineer, due to the high voltages present inside your tube amplifier.
If you have replaced the blown fuse with the correct type and value and it still blows, this could be due to a faulty valve or a fault within the power supply. Do not attempt to replace the fuse with a larger value as this can and will cause more damage. Marshall recommends that you have it looked at by a qualified engineer. To help prevent premature failure, especially in performance venues where the mains power is questionable, you may want to invest in a voltage regulator device, such as the
Furman AR-1215. Many performers consider this to be cheap insurance for their sensitive (and expensive) electronic gear.
Marshall recommends that under no circumstances should you attempt to use your amp until it has been checked by a qualified engineer. Spilled liquids can and will cause more damage to your amplifier if you attempt to use it. Any damage of this kind would not be covered by the warranty.
If smoke is coming from your amp, Marshall recommends that you safely and quickly unplug the amp from the AC mains and do not attempt to use it again until it's been checked by a qualified engineer. If the amplifier is still under warranty, you may return it to the dealer you purchased it from for repair or replacement. (Unless the smoke condition was caused by spilled liquids, in which case it will not be covered by the factory warranty.)
No. The Marshall factory warranty applies only to the original purchaser who obtains the product from an authorized Marshall reseller, and is not transferable. If you purchased the previously-owned amp from a store, check with them, as they may provide a separate warranty for second hand goods. If so, the warranty is with the shop only; not with Marshall.
The PB100 Marshall Powerbrake is an external device that allows the amplifier power section to run at high power levels, and soaks up some of the power output via a series of resistors before the amp output is sent to the speakers. Marshall also incorporates a reactive load (the impedance of the load changes, depending on frequency) and a pair of transformers in the PB100.
A master volume-equipped amp works in a different way than a Powerbrake. The MV control reduces the level of the power amplifier section so that the output tubes do not work as hard. While this accomplishes the goal of lowering the volume, the power amp tubes are not driven to a high enough level at low volumes to produce distortion.
The following sources have a nice selection of spare parts and accessories for Marshall products:
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NOTICE: The information contained herein has not been reviewed or endorsed by Marshall Amplification PLC, Marshall USA, or any other entity. The user assumes all risks of damage or failure to equipment, persons, or property arising from the use of the information contained herein. This page is offered for the sole purpose of presenting the opinions of the various authors opinions on the topics shown. It is not intended to be an all-inclusive or definitive source on the subject. More detailed answers to user inquiries may be obtained from certified Marshall amplification repair centers or dealers. In no event shall the respective authors, MarshallArts.org, The Blame Productions, or their sponsors, affiliates, or assigns, be held liable for acts arising from the use or misuse of content contained at this web site. Repairs should be attempted only by a qualified service center.
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