Tube Amp Not Working: Troubleshooting Guide

Guitarists prefer tube amps because they produce a more authentic sound and are generally louder. However, the original tube amplifiers designed for guitars came out in the 1930s! So, it is no wonder that tube amps require a lot more repairs and replacement parts when compared with solid state amps.

You could always take your amp to a guitar technician when it blows a fuse or needs a new tube, but where is the fun in that? This troubleshooting will act as a guide for you when your tube amp starts acting up. In this article, I will go over some of the main things that can go wrong with your amp, and I will also walk you through how to identify these issues and repair them.

Safety precautions

When you remove the back panel of your tube amp, you will expose yourself to potentially dangerous circuits that can shock you even when the amp is switched off and unplugged. Therefore, it is imperative to take the proper precautions when repairing your tube amp. So wear appropriate safety equipment and take some time to learn the circuitry before poking around at the wires. Tube amp capacitors have a tremendous amount of power and can give you a lethal electric shock if you are not careful.

If you feel uncomfortable working on your amp or have never worked with electrical wires, I HIGHLY recommend hiring a professional for the job. The last thing you want is to get injured. No piece of equipment is worth that!

Common tube amp problems

The most common issues you will have with a tube amp are a broken power tube or a broken preamp tube. These are the most important and most fragile components of the amp, so they will need to be replaced when damaged.

Signs you have a broken tube

Power tubes are the larger of the two types of tubes in an amp. These tubes send the sound signals to your amp’s speaker output and amplify the signal. There are generally 3-5 power tubes in the amp; and all 5 will need to be fully operational for the amp to work and sound at its best. Power tubes are fragile and can easily break or burn out. While tubes can last years, they will eventually need to be replaced. Here are some warning signs that you may need to replace a broken tube:

  • After plugging your guitar into the amp and powering it on, it still is not making a sound.
  • Certain notes cause a rattling or buzzing sound.
  • The tone is off (high-end or low-end deficiency).
  • The amp is much quieter than usual.

If you suspect one of your power or preamp tubes may be bad, open up the back panel of the guitar amp and visually inspect the tubes. If they appear to be cracked or damaged in any way, replace them.

If none of the tubes are cracked, you can still check to see if they are broken by gently tapping them with a wooden stick while the amp is on. If a tube makes a high-pitched clinking sound, it is likely microphonic and needs to be replaced.

What you’ll need to fix it

  • Screwdriver
  • New power or preamp tubes
  • Rubber gloves (optional)

How to fix a broken tube

First, power the amp off and allow the amp to cool. Next, remove the broken tube by pushing down on the metal grip that the tube is secured by and gently rock the tube back and forth until it pops out. For pre-amp tubes, you must first remove the metal casing that is placed over the tube.

Take the new tube, press down on the metal grip and slide the tube into place with the prongs aligned correctly. It should easily move into position. For more information on replacing tubes, read my post on the topic.

Other problems

Broken and faulty tubes is the most common issue you will encounter with your tube amp, but there are also a few other things that can go wrong.

Blown speaker

A blown speaker is an expensive fix and generally involves completely rebuilding the speaker or replacing it altogether. It is VERY rare to blow the speaker of a tube amp because, generally, you will bust your tubes first. The speakers are designed to handle a lot of power for a long time. Nonetheless, it is possible. Older tube amps with the original speaker still wear down over time. If you are playing your amp on high volume for long periods, you can expect to blow your speaker eventually, but doing so will also bring you many other amplifier issues.

Here are some signs you may have a blown amp speaker.

  • A crackling or buzzing sound constantly coming from the speaker.
  • Speaker is not producing any sound at all.

How to fix

Replacing a blown speaker yourself is not something I would recommend. It is a complex procedure that generally results in completely replacing the speaker. Replacing the speaker of a tube amp is complex and can be very dangerous as you will be exposed to many loose wires. I recommend having a professional look at the amp if you suspect your amp has a blown speaker.

Input/output jack issues

The input and output jacks of an amp are another area that may need to be repaired as you are constantly plugging things into these slots. If the amp has a large amount of feedback when you plug your guitar in, minimal sound comes out of the amp when your guitar is plugged in, or the amp is silent, you may have an issue with the input jack. To check if you have a broken input jack, you need to open up the amp and remove the electronics from the amp’s body.

What you’ll need

  • Screwdriver
  • New input jack (if needed)
  • Soldering iron

How to fix

First, remove all the screws securing the electronic transformer to the amplifier box. Next, remove the transformer from the box and place it down safely.

Check the input cables to see if there is any visual damage. If any of the wires are loose, use a soldering iron to reattach them. If the input jack is damaged beyond repair or you cannot fix it, replace it with a new input jack.

Knobs not working

The volume, tone, gain, and other knobs are yet another area that may get damaged or need replacing over time. You will likely need to fix or replace the knobs if they are not working as they are supposed to or if there is unusual feedback when they are being used.

How to fix

If one of your amp “pots” or knobs is not working, remove the plastic cover and thoroughly clean the cover and the metal “pot.” Sometimes, the fix is as easy as cleaning it up.

If this doesn’t work, remove the electronic transformer by first removing the screws holding it. Once the amp’s transformer has been taken out, take a look at the backside of the knobs, clean them, and spin the knob around 10-20 times. This helps remove some corrosion from the controls, which may be preventing the “pot” from functioning properly. Also, be sure to check the soldering around the interior side of the knob control. Finally, if any wires are loose, resolder them.

If all else fails, your final course of action will be to replace the knob completely.

Power cord shorting out

I have spent hours trying to work out the issue with my tube amp when the issue was simply that my power cord was shorted out. If the amp is not working, even when you have plugged it in and turned the power off, your first troubleshooting step should be to switch out the cable. If the new cable fixes the issue, you now know that the source of the problem was the cord.

How to fix

There is not necessarily a feasible way to repair a power cord that has shorted out. You’ll likely need to purchase a new power cord to replace the broken one.

Wrapping up

Tube amps sound great and provide the classic tone many rock guitarists seek, but they are high maintenance. Any tube amp owner will need to learn how to take care of the amp and fix any issues that may arise. 

If you have more questions about your tube amp or your musical career in general, feel free to reach out, I am always happy to help!