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Amp Troubleshooting

The majority of service problems that occur from time to time through normal wear and tear on group equipment are often minor ones. Musicians need only have a small amount of practical know-how to do servicing jobs in order to keep themselves out of trouble when their equipment stops working or malfunctions.

The majority of hums, clicks and bangs encountered with amplification set-ups can be found amongst the mains cables, speaker leads and instrument leads and quite often the 'NO SOUND' amplifier is simply the result of a blown fuse or a wire that has detached itself from a plug connection. Bands and musicians are often situated where service is not readily available or where the service charges may be prohibitive if travelling abroad, and, to help you tackle service jobs on your instrument amplifier we have drawn up a schematic diagram that takes you through the servicing check steps in a logical way. We hope that this will be of practical use to you and it will help you to keep on playing between major services.

To make use of the diagram it is necessary to carry basic spares and a tool kit. Bands on tour always carry valve replacements and fuses or transistors and driver boards, whatever the equipment requires. Great care should be taken when changing valves to ensure that you use the identical coded valve as a replacement. If equivalent valves are used check that the pin numbers are the same as the valve you are replacing. For American amplifier valve spares contact a top dealer or the Dupont agent to get the correct valve as sometimes an equivalent does not give the original sound!

Switch off the amplifier before valve changing, leave for a few seconds then exchange the valves and switch on. If a replacement valve glows in a distressed manner after half a minute or so switch off the amplifier and take it to a good service engineer.

Transistor amplifiers are not as straight forward to trouble shoot and we would recommend that you carry fuses, spare power transistors, a driver board (P.C.B.) and integrated circuits when you go on tour. To change the power transistors if they are a plug-in arrangement can be quite a quick job, and if the driver board for the power stage is plug-in this can also be quickly done. However this will only help in the event of an amplifier that has stopped working due to an output stage fault, if the amplifier is distorted components in the pre-amplifier stage may need replacing (integrated circuits or small signal transistors) and if you are not technical leave it alone and take it to a service engineer.

This is a first step in fault finding for the non-technical musician who would like to trouble shoot himself out of blowing the gig.

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International Musician & Recording World - Copyright: Cover Publications Ltd, Northern & Shell Ltd.


International Musician - May 1975

Donated & scanned by: Mike Gorman


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