How to Diagnose Marshall Amp Head Problems

Written by ryan cockerham
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How to Diagnose Marshall Amp Head Problems
Amp heads can develop distinct problems separate from the speaker unit. (amplifier image by Darko Draskovic from

Professional guitarists around the world rely on the Marshall amp head to supplement their recording and performance gear and provide a consistently high level of quality and performance. Like all engineered products, however, the possibility of malfunctions or problems does exist. Identifying and repairing issues with the amp head is an easy process. By checking the fuses and valves, an accurate solution to the problem can be formed quickly.

Skill level:

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Things you need

  • Speaker cabinet
  • Electric guitar
  • Instrument cable

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  1. 1

    Connect the faulty amp head to the speaker cabinet and plug the guitar into the amp head using the instrument cable.

  2. 2

    Lower the volume level on the amp head to a very low setting. Turn on the amp head and speaker cabinet. Strum the guitar and gradually raise the volume on the amplifier to a comfortable level.

  3. 3

    Listen carefully for any defects in the sounds coming out of the speaker cabinet. The most common source of problems will be the preamp valves in the amp head. If you hear any high-pitched whistles, a sudden loss of volume or a sudden loss of high-range frequencies, the preamp valves are the source of the problem. Turn the power off on the unit. Replace all the preamp valves simultaneously by unscrewing the front grill on the amp head, gently pulling the faulty valves out of their sockets, and replacing them with the new valves. The valves have a grouping of pins on one end that will line up with holes in the socket.

    This will lead to a much higher quality performance from the amp head.

  4. 4

    Check for any blown fuses inside of the amp head. If any of the HT or main fuses have blown, this is a very clear indication of valve failure.

Tips and warnings

  • The output valves on the preamp are responsible for the quality of sound your amp head will produce. Depending on how regularly the amp head is used, the experts at Marshall predict that "output valves will last 18 to 24 months." Replace your valves within this time frame to avoid a majority of the problems you might experience with your amp head.
  • Any time you are troubleshooting problems with your amp head, turn the power off on the unit before you attempt to remove fuses or valves. The risk of severe electric shock is great when working with audio equipment that draws a large amount of power.

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