Tube Faults

Common Vacuum Tube Issues and How to Spot Them

If you're an audiophile, a vintage electronics enthusiast, or a musician who relies on high-quality sound, you probably know the importance of vacuum tubes. These little powerhouses amplify and control signals in everything from hi-fi audio systems to guitar amps. However, like any piece of gear, vacuum tubes aren’t immune to wear and tear. Understanding the most common problems can help you keep your equipment running smoothly. Here’s a quick rundown of some typical vacuum tube faults and what to look out for.

1. Burned-Out Filament

This is the simplest and most common issue. Just like a light bulb, the filament inside a vacuum tube can burn out, leaving you with a tube that doesn't work. A tube with a burned-out filament won’t light up, and your equipment will either be silent or completely dead.

Signs to Watch For:

  • The tube doesn’t glow when powered on. (often preamp tubes are hard to see glowing in daylight, try looking at them in a dark room at night)
  • Your gear produces no sound or cuts out entirely. Mind you, there can be a lot more issues that causes no sound.

What to Do: If the filament’s dead, it’s time to replace the tube. Keeping a few spares around can save you a lot of hassle. We recommend always keeping a spare "Good tube, one you know works) that way if you have any concenrs you can remove tube one and rpelace it with the good one, still no sound, then replace tube one and try tube two with the known good tube. 

2. Microphonics

Have you ever heard a strange ringing or feedback sound from your amp when you weren’t even playing? That’s likely caused by microphonics—when your vacuum tube picks up vibrations and noise. This is particularly common in high-gain amps and can be a real annoyance if you're trying to get clean, clear sound. Whilst tubes are tested for micrphonics, you can have sensitive sockets (think of a nerve in tooth ache) these are often cause by poor manufacturing practices or a build up of dust particles on your sockets or circuit board which will provide conductivity. Customers will run an amp for years, then buy a new preamp and complain that the tube is microphonc when in fact it is just a strong tube and the socket has built up dust layers and now the socket or board is conductive. 

How to Spot It:

  • Tapping the tube or even moving your amp makes noise come through the speakers may show is sounds micrphonic but remember this could still be your amp
  • You hear feedback, ringing, or strange sounds even when you’re not playing.

What to Do: If you’re dealing with microphonics, you’ll probably need to replace the tube. Opt for high-quality tubes that are less prone to this issue. You may alos need to have a tech give your amp a good clean. We have testers that check your preamp tubes for microphonics.

3. Cathode Poisoning

Cathode poisoning sounds pretty dramatic, but it’s just what happens when a tube hasn’t been used for a long time. When a vacuum tube sits idle, the cathode can develop a layer that interferes with electron emission, making your sound weaker over time.

What to Look For:

  • The sound gradually weakens, or you get low output even when everything’s powered on.
  • The tube looks old, but you haven’t used it that much.

What to Do: The best prevention is regular use. Don’t let your gear sit too long without firing it up. If you do experience this, rejuvenation techniques might help, but often the easiest solution is just swapping in a new tube.

4. Grid Emission

Grid emission occurs when the control grid inside the tube becomes contaminated or overheats, causing erratic performance. This can lead to distortion or even humming sounds in your audio.

What to Listen For:

  • Distorted sound, especially when you turn up the volume.
  • Inconsistent performance, with your equipment cutting in and out or acting unpredictably.

What to Do: Replacing the tube with a higher-quality one should solve the problem. It’s a good idea to invest in tubes made from better materials to avoid this issue in the future.

5. Gassy Tubes

Vacuum tubes are sealed, but sometimes air can leak inside. When this happens, the tube becomes “gassy,” and this can lead to noise, reduced efficiency, or complete failure.

What You’ll Notice:

  • The inside of the tube looks cloudy or hazy.
  • The equipment might hum or produce static noise, even when it’s supposed to be silent.

What to Do: Unfortunately, gassy tubes can’t be fixed, so you’ll need to replace them. Keep an eye on the quality of the tubes you’re buying to avoid this issue down the road.

6. Internal Shorts

An internal short happens when different components inside the tube touch each other, which can cause loud pops, buzzing, or even sparks. This can be scary if you’re not expecting it and can cause immediate equipment failure.

Signs of a Short:

  • A loud pop or buzz coming from your equipment.
  • The tube might spark, and your gear could stop working altogether.

What to Do: Turn off your gear immediately to prevent further damage. The tube will need to be replaced, and it’s worth checking your equipment for any other issues to ensure nothing else got damaged.

7. Loss of Vacuum

When you see a tube with what looks like white poweder inside the tube you will find this is likely due to a loss in vacuum. This generall happens when the tubes are being replaced and stress is placed on the pins for the tube. Remember: There are steel pins protrucding from glass tubes that hold a vauum. Pushing these pins in a way that adds stress may cause the glass to crack. From time to time a customer will say it was in the amp working and then 20minutes later it stopped working and it was white. Once again, it is likely that the tube was pushed in without viewing the socket properly and the pin has gone down the side of the sicket pin holder and and put stress on the tube, as the tube heats up it becomes weaker, eventually cracking.

Signs of a loss of vacuum:

  • A white poweder look inside the tube.

What to Do: There is nothing you can di, the tube is no longer able to be used, you must replace the tube, being careful on how you install the next tube.

The Importance of Regular Tube Maintenance

Just like your car needs regular check-ups, your vacuum tubes do too. Keeping an eye on your tubes and swapping out faulty ones can save you from larger issues down the road. For those in Australia who are passionate about their sound—whether it’s for a hi-fi system, a guitar amp, or some vintage radio equipment—staying on top of tube health is key to getting the best performance. Remember, we are the one stop shop for reliable vacuum tubes.

Where to Buy High Quality Vacuum Tubes in Australia?

Of course, the best way to avoid these problems is to invest in high-quality vacuum tubes from the start. If you’re shopping for tubes in Australia, make sure you’re buying from a trusted source that carries reliable, top-tier brands. Whether you’re upgrading your sound system, replacing a worn-out tube, or fixing up a vintage piece of gear, the right tube can make all the difference.

At Evatco, we offer a wide selection of premium vacuum tubes perfect for audiophiles, musicians, and vintage electronics enthusiasts alike. Explore our range and find the ideal tube for your needs. So, if youre looking for a place to buy vacuum tubes online in Australia, come to Evatco.com.au where we have the largest range, in fact we are the largest Australian vacuum tube suppliers. 

We carry a hugh range of Audiophile vacuum tubes, Guitar amp tubes, Vintage electronics tubes, and all located here in Australia