How to Troubleshoot & Repair a Guitar Amplifier

Dust can gather behind the dials, causing the potentiometers to crackle.

Your guitar amplifier requires maintenance and occasional repair. You will notice from time to time that your amplifier emits a strange hum or an unusual buzz. These are signs that your amplifier is malfunctioning. In other cases your amplifier may stop working, in which case you need to replace certain parts. Solid-state amplifiers are less likely to break down than tube amplifiers because transistor technology used in solid-state amps is more reliable. You may need to occasionally change fuses and transistors in a solid-state, but this is unlikely.

Things You'll Need

• Phillips or flat-blade screwdriver
• Replacement guitar cable
• Replacement fuses
• Replacement power tubes
• Replacement preamp tubes
• Soldering iron
• Cotton cloth
• Plastic-safe contact cleaner and lubricant
• Flashlight

Instructions

1. Replace your guitar cable. Start the troubleshooting process by using a new cable. Old cables can create buzz that is often mistaken for a problem within the amplifier.

2. Plug in your guitar and turn on the amplifier. With the volume turned to zero, power up your amplifier. Now gradually increase the volume and play the guitar. If the amplifier powers up without problem, your power section is working fine. If the amplifier fails to power up or is intermittently cutting out, inspect the power section. Start by unplugging the amplifier and replacing the fuse in the plug. If this does not work, remove the back of the amplifier using the appropriate screwdriver and replace any burned-out fuses in the power section. If you have a tube amp, replace any burned-out power tubes. You'll find the power section by observing at which point the power cable connects to the amp.

3. Inspect the preamp section of the amplifier. Amplifiers have three main sections --- the power section, the preamp and the speaker. If you can turn your amp on but get no sound from it, there is a problem in either the preamp or the speaker. If you have a tube amplifier, look for any burned preamp tubes. Burned-out tubes have a discolored filament. If you spot one, switch off the amplifier and replace the tube with an identical one. If all the tubes are working but there is still no sound, check for burned-out fuses and replace any damaged ones. With solid-state amps, look for burned-out transistors. This is a less common problem, but the solution is as simple as changing a tube. Just pull out and replace the transistor.

4. Remove the preamp completely and clean and lubricate the potentiometers at the back of each dial with the cotton cloth, plastic-safe contact cleaner and lubricant. Dust and grime that collect here can cause unpleasant sounds.

5. Check that the speaker is connected. If your amplifier powers up and creates sound but is producing a humming or rattling, it is likely to be a problem with the speaker. Shine a flashlight on the speaker and look for any rips in the speaker cone. If your speaker is ripped you'll need to replace it. Also check that the speaker is properly connected. Examine the wires and resolder any loose ones.

Tips & Warnings

• When replacing parts, take the original to the store to ensure that you get a like for like replacement.

• Always wear latex gloves when handling amplifier tubes. Oils from the skin can create heat spots that weaken the glass.

• Always disconnect the guitar and any other components from their power source before working on them. Allow tubes and other components to cool before handling them.

References

• Learn To Play Rock Guitar: Guitar Amp Maintenance
• Athens Musician: Tubes Explained for Dummies Like Myself
• Guitar Player: How To Replace Speakers

Resources

• K Bapps: Tube Care