How To Tell If Amp Tubes Are Bad – Noisylabs

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Tube amplifiers are fragile, but necessary. We can't live with them, and we can't live without them.

For audiophiles, tube amps are another way to geek out about audio.

What's frustrating about tube amps is the lack of equipment for testing. There are a lot of symptoms of a bad tube amp, but there isn't a device users can use to test what condition an amp is in directly.

Sometimes the damage is obvious which leaves out a lot of guesswork. But other times it isn't obvious is where concern creeps in.

With this post, we hope you know how to tell if your tube amps are bad.

What Does A Bad Tube Amp Look Like?

The easiest check to see if you have bad tube amps is to shake them. 

While you shake them, you'll hear rattling inside, but don't mistake that from all the components already inside. The sound coming from the rattling needs to sound different from the other tubes to let you know you're dealing with a bad tube amp.

You need to look out for any broken parts. To find out if you have a bad tube amp, try shaking all the other amps, and whichever differs in sound from the shaking needs further inspection.

The second tell-tale sign to look for in bad amps are the getters' color. This is the coating of an amp which is found either on top or on the sides of an amp. It can also cover both the top and sides simultaneously.

how to tell if amp tubes are bad


A healthy color specturm for a getter is black/silver/grey. You don't want your getters to be white. A white getter means a small leak has happened to your tubes.

Another color to look out for is purple. This also signifies leakage.

The color you want is orange. An orange color means your tube is glowing to some degree. There are varying degrees of orange in different tubes, but that isn't a concern. Start worrying if your tube is cherry red.

Common Symptoms Of Bad Tube Amps

Amp is dead 

Even if your amp seems dead, it's always a good idea to test it. One way of doing this is gradually increasing the volume.

If you don't hear anything at its lowest volume setting, reserve judgement until you've hit maximum volume power. 

If you still don't hear anything, then it's a good indicator your amp is dead.

If your amp doesn't respond to volume changing then check for blown fuses.

The remedy for this is to replace the fuse with another fuse. 

When replacing your fuse, you need to remember 2 concepts.

Match the amp rating and make sure your voltage rating is suitable for your wall outlet, or current surroundings.

Remember, voltage can kill a person if enough voltage is applied. An average wall outlet has a voltage of 125. Humans can die from 100 volts if applied correctly. 

But it isn't specifically voltage which kills, it's the current in proportion to the voltage which kills.

Any fuse can make an amp look dead. Common areas where fuses are blown are on a circuit board, and wires with fuse holders.

Once you've replaced the fuse, you can test your fuse by using a multimeter.

how to tell if tube amps are bad

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Excessive Humming Or Buzzing

Our first reaction to humming or buzzing is to check the speaker connections.

But what do we check next once everything is connected?

One area we check next is the circuit. Since noise has to pass through the circuit, this is a logical area.

If you notice a change in humming or buzzing when volume changes, then this is a cause of noise entering the circuit before the control.

By control we are talking about the volume control. 

Another sign we look to tell if your tube amps are bad are the solder joints. Solder joints melt under heat even if it's new. Even if a little solder goes missing, it'll screw up the current's circuit.

Some quick fixes for humming or buzzing are cables. Changing the cables if you have a guitar cable is a plausible solution. 

Going back to what we're saying before, fixing your tubes also eliminates excessive humming or buzzing. 

Other, less obvious solutions is moving your amps to another location.

If you ever have your phone near your computer while it's playing, then you might've noticed some static. This is due to radio frequency interference.

The frequency interference happens due to waves emitting onto other devices disrupting it. If you have humming or buzzing problems, then look out for these signs.

Sometimes the "problem" is a quick fix. It's all about knowing what you're dealing with. 

These are only some of the problems, so it's on you to do more research if none of these solutions work and the problem persists.

Loss Of Power

Another sign of bad tubes is when the amp performs less than its power's capability. One reason amps lose power is due to mistreatment or age. Even if you have high grade material, over time, transistors and capacitors will degrade given enough time.

Loss of power can also happen due to damage. If you were to leave your amp outside, heat will damage it by rusting it up. A capacitor in an amp is built like a battery so it's not unheard of for a capacitor to leak.

One reason for leaking is over exposure to heat.

Other reasons your amp loses power depends on how much power it gets. If it's overpowered or under powered, it'll hurt your amplifier.

Crackling

Crackling coming from your amp comes from poor tube connection. A simple fix is to adjust the position of your tubes.

Although simple, it can be time consuming. to go through each tube to see if it was the problem. But that's what it takes to fix a crackling amp. This also works for excessive humming and buzzing. 

Microphonics

Tube amps have a tendency to amplify any environmental noises it comes in contact with. An example of this is if you bumped into one of the preamps. If you bumped into it, that bumping noise will be exaggerated by the amp.

The trick is to find the noisiest tube, because the noisiest tube is the bad tube. Most tubes, if not all, emanate sound when messed with. But when one tube stands out among the rest, then that tube is usually the bad one.

Voltage Readings

Before measuring your voltage, make sure you know the average voltage readings for your amp. This lets you know what's normal and what's not for your readings.

An above average voltage reading is a cause of a non-functional tube not drawing current from the power supply. If the voltage readings are low, this causes multiple problems.

The first which comes to mind is a component on the circuit board dragging the current. Most of the time circuit boards operate in sync, but there are times where one tube pulls more current than it should.

This happens from a short or incorrect component value from a new amp.

Sometimes you can't even get a reading. When this happens, you need to check the power supply. This is similar to having a dead amp. To make sure your power supply is actually broke, check on solder joints and wiring. 

Furthermore, check on your capacitors and resistors. Resistors not working makes it hard for the circuit to regulate current.

Capacitors on the other hand distribute energy. Check to see if your capacitors are working to find out if it's responsible for the power situation.

Specific Tube Amp Problems

Preamp Tubes

Preamps have 2 common problems you'll notice when things aren't going right. You'll notice either the noise or its microphonics.

The tricky part is when you have multiple tubes. Having to figure out which tube is bad deceives people at times. The main reason why that happens is because a tube may not even sound bad, but still have problems.

You can try tapping on one tube to see if anything has changed. If you tapped it and nothing happened then assume it's alright. Beware that tubes will give a slight ring when you tap it though.

In situations like this it's important to carry an extra tube you know is fine. This lets you swap tubes one at a time to see which one is the culprit.

A common culprit for preamp tubes are the V1 tubes. If you don't know where to start then this should be your starting point.

how to tell if amp tubes are bad


The 2 common problems can be broken down by a few simple characteristics.

For noise, if you hear crackling, popping, or hissing, then you know it's noise.

Microphonic tubes exhibit humming, feedback, and squealing. For those who don't know, feedback is that high-pitched noise similar to nails on a chalk board. It makes everyone want to cover up their ears similar to a squeal.

Power Tubes

Power tubes are also easy to read.

There are 2 problems you're looking for to determine whether they're bad.

The first is the tube is bright red. 

This means the power tube is being overpowered. You need to turn off the amp immediately. Wait 5-10 minutes before starting it up again. If the problem persists, then you need to replace the tubes.

The second problem is a blown fuse.

If this happens then replace the fuse. If it happens again, then replace your power tubes.


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