How to Tell If a Vacuum Tube is Bad

How to tell if a vacuum tube is bad? Well, there are some symptoms that will let you know that you have a problem with your vacuum tube. Of course, this may require some testing. If you want to know the condition of your vacuum tube whether it is in good or bad condition, then this article is for you.

In the early twentieth century, vacuum tubes were used as a special component in radio to pass electrical signals. As you may know, a vacuum tube is a close-vacuum electrical tube that controls the passage of electricity between its two electrodes. Once current travels through a vacuum tube, the filament associated with the cathode heats up. Due to the magnetism of the charge, the heated cathode produces electrons that go straight to the anode. But they are outdated currently.

In this article, we will tell you how you can understand if your vacuum tube is bad or if there is a problem. So keep reading the rest of the article to know the process of examining vacuum tubes properly.

How to Tell If a Vacuum Tube is Bad

Interestingly, although vacuum tubes are outdated technology, they still exist in some amplifiers and other appliances. Examine your vacuum tube for signs of damage and listen for the sound it creates as a fast test. You can also attain a tube with a test chart if you are aware of tubes.

There is another effective way to test a vacuum tube and that is a tube tester. It is electronic equipment used to test the properties of a vacuum tube. Below we will discuss some of the symptoms that will help you to know the problem of your vacuum tube.

Visible Symptoms

  • We will look at some visible signs. This is the initial stage for checking the vacuum tube. This means that the eye can guess what is causing the problem or where it is happening. The first symptom is that each tube has a heater filament that gives off a warm orange hue during work. However, in some tubes, it is more intense than in others. But the thing to note here is that it will glow too much.
  • Conversely, filaments of some tubes cannot be seen as they remain hidden. At this stage, you check whether the tube is cold or hot. Remember that the filament must be heated while working. Otherwise, the tube is likely to be useless.
  • You need to check the condition of the getter. The upper part of the tube is coated. Normally, the color of this coating is black, gray, or silver. If you notice in the white coating tube, then you need to understand that there is a crack. In this situation, it is necessary to add a new tube.
  • When checking the vacuum tube, if there is a purple aura around the components inside it, it indicates that there is a leak. But don’t mess with the blue glow this time. Now fix a new tube instead of the old one.
  • The vacuum tube may turn red over time. If the inside of the tube coating turns red, replace it quickly. The presence of red color in the tube means that the electrical gadget does not fit properly. As a result, it will fail to manage the current and may even ruin the gadget as well.

Reveal the Aura of the Vacuum Tube

Insert into an electrical gadget to reveal the aura of the vacuum tube. Connect the tube to the guitar amplifier or testing tube. If you do not have a testing tube, use whatever pipe-using device you have. Turn on the device to activate the tube.

Now check if there are orange, red, purple colors. These colors are a sign that your vacuum tube is healthy. However, when heated in the filament of the pipe, the orange color will glow inside it, especially when the sun goes down.

Finding filaments is often difficult. However, if you can’t see any color glow, it doesn’t mean that there is a defect in the vacuum tube. There are some tubes whose color is sharper than the rest. If you don’t see any color glow in the vacuum tube, try touching it. At this time no one is going to touch with a full hand. This will burn your hands. Just touch lightly. If you feel intense heat then there is no problem in the tube.

Additionally, after some time of placing your tube in the electric gadget, if it is not turned on, then it is understood that it is broken. And a broken vacuum tube is called a cold tube. This means that the device is fused and it is time to install a new one.

Check the Presence of Shaking

Check if there is any shaking in the tube. Because it can ruin the components. You may feel the presence of trembling when examining the tube. If something like that is in your eyes, it is best to set up a new tube as soon as possible.

Examine the Noise

If your vacuum tube breaks or makes any noise, the tube will be considered bad. Moreover, if you can detect any loose piece twisting inside the tube then that tube is deadly harmful and unacceptable. To test this sound of a vacuum, you take a pencil and gently press or tap on each tube with it. This will make the faulty tube sound a little louder than any other tube. This problem is most often caused by microphonic noise.

Go With a Tube Tester

A tube tester plays a unique role in testing a variety of vacuum tubes. So buy a tube tester according to your budget. This technology is currently being used extensively. Such a Mutual Conductivity Tester will allow you to test the efficiency of the tube. On the other hand, the exhaust tube will help to see if anyone’s tube is operational.


Safety must be a priority during vacuum tube tests. For this, we are recommending you to wear hand gloves. Because when activated, the vacuum tube will be very hot which can burn your hands. Hopefully, this post will be useful for you to detect or tell if the vacuum tube is bad. Protection Status
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