How to Troubleshoot a Tube Guitar Amplifier

Replacing blown tubes is a normal part of routine tube amplifier maintenance.

The warm, fat tone of tube amps has drawn musicians away from their solid state cousins for years. Before you can plug that beautiful Telecaster in however, you will need to make certain your tube amp is functioning properly. Knowing how to troubleshoot a tube amp is not difficult to master and should be a part of every serious musicians skill set.

Things You'll Need

• Effects cable or guitar cable
• Electronic contact cleaner
• Multimeter

Instructions

1. Check the fuses. Flick the power switch on. Look to determine if the power indicator -- usually a red light, is on. Change the AC main fuse if no light is present.

2. Inspect both the power tubes and the preamp tubes visually for voltage. Determine if every tube is glowing as even one shorted tube can cause the amp to malfunction. Replace tubes if necessary.

3. Replace multiple tube outages if necessary by inserting one new tube at a time as tubes are often used in a series and a blown tube can effect all the tubes in a series.

4. Test the jacks of the series effects loop. Insert an effects cable or short guitar cable into the "Send" jack and the opposite end into the "Return" jack. Listen to determine if the amp sound is intermittent as this is an indication of corrosion of the jack's switching contacts.

5. Remove the cable if sound is produced and spray a small amount of electronic contact cleaner in each jack. Insert and remove the cord into each jack eight to 10 times leaving the cord inserted inside each jack when finished.

6. Let the amp sit for an hour while the spray dries before attempting to test the amp again. Replace the jacks if intermittent sound continues.

7. Test the speaker and its corresponding connections. Disconnect the speaker from the amp if possible. Connect another speaker using a different cable and test the amp again. Replace or repair the speaker or speaker cable if the amp works properly with the second speaker and cable.

8. Check the resistance of the speaker to determine if electrical current is flowing by using a multimeter if the amp still is not working after speaker or speaker cable replacement. Disconnect the speaker from the amp output.

9. Switch the multimeter to resistance mode with a reading set between three to 14 Ohms. Check resistance on combo amps by measuring across the speaker terminals. Measure extension cabinets by using a working speaker cable and checking resistance between the sleeve and tip.

Tips & Warnings

• Take your amplifier in to a licensed technician for diagnostic tests if all else fails.

References

• Premier Guitar: Tube Amp Troubleshooting 101

Resources

• Fretland: Tube Amp Tips