Chances are that one of your tubes (valves) has failed. If your amp is still in manufacturers warranty take it back to the place where you bought it. Otherwise you need to identify which tube has gone and replace it. This will entail gaining access to the inside of the amplifier case. BEWARE this can be VERY DANGEROUS if you don't know what you are doing. IF IN DOUBT TAKE IT TO A REPAIR SHOP Always disconnect from the mains electricity supply before dismantling. Once you have got the case off you will need to plug the amp in again and turn it on - you don't need to plug a guitar in just the mains supply. TAKE GREAT CARE not to touch any metal parts. Look at each of the valves (there are some on the pre-amp stage behind the front panel as well as on the main amplifier chassis) they should all be glowing a nice bright red colour in the middle if they are healthy. If any valve is not 'lit up' that will be the faulty one. DO NOT TOUCH IT - apart from the high voltage electricity associated with them valves get very HOT. Turn the amp off, unplug the mains supply and WAIT at least 10 minutes for it to cool down again. Carefully slip the metal retaining spring off the top of the valve and, gripping it with a tissue or soft cloth, gently pull it out with a slight rocking motion. Carefully note down all the numbers and letters on the valve to identify the correct replacement. There are literally hundreds of different valves - putting the wrong one in may cause further damage to the amp.
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Chances are that one of your tubes (valves) has failed.
If your amp is still in manufacturers warranty take it back to the place where you bought it.
Otherwise you need to identify which tube has gone and replace it. This will entail gaining access to the inside of the amplifier case. BEWARE this can be VERY DANGEROUS if you don't know what you are doing.
IF IN DOUBT TAKE IT TO A REPAIR SHOP
Always disconnect from the mains electricity supply before dismantling.
Once you have got the case off you will need to plug the amp in again and turn it on - you don't need to plug a guitar in just the mains supply. TAKE GREAT CARE not to touch any metal parts.
Look at each of the valves (there are some on the pre-amp stage behind the front panel as well as on the main amplifier chassis) they should all be glowing a nice bright red colour in the middle if they are healthy.
If any valve is not 'lit up' that will be the faulty one. DO NOT TOUCH IT - apart from the high voltage electricity associated with them valves get very HOT.
Turn the amp off, unplug the mains supply and WAIT at least 10 minutes for it to cool down again. Carefully slip the metal retaining spring off the top of the valve and, gripping it with a tissue or soft cloth, gently pull it out with a slight rocking motion. Carefully note down all the numbers and letters on the valve to identify the correct replacement. There are literally hundreds of different valves - putting the wrong one in may cause further damage to the amp.