The Basics of Tube Amp Upkeep and Maintenance

It’s a special moment in any guitarist’s life when they plug into their first tube amp and hear that heavenly breakup—the legendary tone that forms the basis of everything from Chuck Berry to Stevie Ray Vaughan to Metallica.

With classic tone at your fingertips, you’re probably excited to crank your first tube head or combo and see what you can make with its monstrous power. But before you wake the neighbors, it’s important to know how to take care of your new tonal investment with these handy upkeep and maintenance tips.

Basic Safety

Sure, guitar is all about letting it rip, but some common-sense safety tips will help you get the most out of your rig without damaging it or, more importantly, risking your own health and safety.

As with any electronic device, liquids are a big no-no. Though it might be tempting to rest your favorite brew on your amp in between solos, the vibrations produced by a typical amplifier make it almost guaranteed that your beverage of choice won’t stay put. You could easily get electrocuted or, at the very least, cause your amp to fail.

You also want to make sure that you’re using a grounded, three-pronged power supply. While some people try to clip off the bottom prong or use a two-pronged adapter, this is extremely dangerous. In layman’s terms, you’ve taken away the electricity’s escape route in case of a crossed wire, which means that it might try to escape through your amp chassis, your guitar, or you.

How to Operate Your Tube Amp

With solid-state amps, you just switch on the power and play. But tubes are actually a relic from a different electrical era, and, as such, are a little more temperamental about their power supply. Thus, to take advantage of their awesome tonal character, we have to deal with their lo-fi quirks.

The best way to prolong the lifespan of your power tubes is to turn the amp on and off properly. This means giving your tubes time to warm up in between each use. Fortunately, tube amps have two switches for this exact purpose: On/Off and Standby.

On/Off and Standy switches

To turn your amp on properly, make sure your Standby switch is engaged. Set the On/Off switch in the On position, then give it a minute or so to warm up. You should see the power tubes inside the amp glowing orangey-red, which means you can flip the Standby switch off and start rocking. You may notice that your tubes burn a lot brighter while you’re playing, which is because they create a lot of heat energy while producing your awesome tones.

Some amps let you change the amount of power hitting the tubes with a switch marked “Pentode/Triode” or with different watts ratings. It’s probably safest to switch the power supply only when the amp is all the way off. Remember, tube amps can store up serious voltages, and messing with power supplies could shorten tube life.

If you have a head and cabinet set up, make sure that your amp head is always plugged into a speaker cabinet (using only speaker cables) to avoid damaging the output section of your amp. More importantly, make sure that you’re matching the correct number of ohms (Ω) from you amp’s output to your speaker cabinet’s input. There are a few different configurations that might work, but the most tried-and-true method is to match the same number from output to input.

When and How to Replace Tubes

Just to get the ball rolling, there are two main types of tubes in a guitar amp: preamp tubes and power tubes. It’s easy to tell the difference between the two from their size—power tubes are big and preamp tubes are small.

12AX7 Preamp Tubes

Preamp tubes typically form the gain or distortion section of your amp, though they can also be used in reverb and tremolo circuits, and rarely need to be changed unless they go microphonic—that is, if they begin to pick up vibrations and transmit noise (more on this below). Power tubes, as their name implies, are responsible for your earth-shaking, dead-waking volume.

These heavy lifters degrade over time, usually losing some of their sparkle, at which point you’ll need to replace them in matching sets. Even if just one of your tubes is causing problems, you’ll have to check your amp’s manual to find out which other tube it’s matched with and change that one as well. Once you’ve located the problem pair, wait at least 15 minutes after you turn off your amp before touching anything inside it. Some recommend wearing rubber gloves to avoid burning your hands or getting oils from your hand on the tube, but this probably not essential.

Power amp tubes can be a little tricky to remove, since they have a guide hole on their bottom surrounded by several tiny prongs and may also be held in place by small metal flaps. Push these metal wings down with one hand and gently pull the power tube out with your other hand in a wiggling or circular motion. To put in new power tubes, simply reverse the process. Align the guide hole and small prongs with the socket and gently push it in with a wiggling or circular motion.

6L6 Power Tubes

Replacing a preamp tube is a much easier process. And you do not have to worry about matching pairs. Just replace whichever individual preamp tube is dysfunctional by pulling the tube straight out of its socket and plugging in a fresh replacement.

There are some visual indicators that can clue you in on when a tube is on its way out.

While playing, check your power tubes to see if one is burning noticeably less bright than the others or is turning a different color. Many tubes will start to turn white when their vacuum seal is wearing out, which is a dead giveaway that it’s time to change. Hot spots can also form on tubes if someone touched the tube with bare hands. And, obviously, if a tube is cracked or shattered it will definitely need to be replaced.

You might also notice humming or extra phantom notes coming from power or preamp tubes that have become microphonic. You can test the tubes by turning on your amp and lightly tapping each one with a pencil, chopstick, or other small wooden tool. If they clink like normal glass would, they’re probably functioning normally. But if they make strange rattling or thudding noises through the speaker, they are most likely microphonic and will need to be replaced.

Testing and Setting Your Tubes’ Bias

You may have heard something about tube biasing, and how it’s never safe to do it yourself. Well, if you have a few electronic tools and patience enough to not get yourself electrocuted, it’s actually not that daunting. Of course, if you’re not familiar with electronics and you don’t feel comfortable taking the back panel off your amp, there’s no shame in taking your amp to a tech.

But first, as a simple primer, why is bias important and why should you care? Because it lets you set the breakup point for your amplifier.

Bias adjustment pots

Remember that your guitar turns an acoustic vibration into an electrical signal through the pickups, and biasing sets how much voltage hits your power tubes. Set it too high, and you’ll start to lose clarity before you turn it up past 3; too low, and it’ll be hard to get any crunch at all. Bias also allows you to optimize your tube life, since running them with a hot bias will blow through power tubes faster than you can scream “High Voltage” à la Bon Scott.

Most modern amps have a biasing potentiometer and bias test point inside the amp. Consult your amp’s instruction manual to locate these components. Older amps are usually fixed bias, meaning it’s probably better to take it to a tech who can install the components required to adjust the bias. Some amps are self-biasing, meaning you don’t really have to worry about doing anything yourself. (If you’re lucky enough to have such a model, feel free to skip to the next section.)

The general safety rule that you should always follow when working on amps is the “one hand in your pocket” rule. If you have one hand in your pocket, you’ll avoid contacting a ground point in the amp while also touching a dangerous positive voltage, which could kill you. Since you’re running the amp at full power during this process, it’s better to probe with one hand, go slow, and proceed with caution.

Using a multimeter set to test DCV at 200m, attach the ground wire to the chassis and find your amp’s bias test point. After you’ve tested the bias, put down your multimeter probe, make a small adjustment to the bias pot, and test it again until you’ve reached the optimal bias range specified in your amp manual. You can also test it out (once you’ve closed the amp back up) to see if it’s had the desired impact on your sound. If not, just open it up and repeat the process again.

Other Essential Upkeep

Though tubes are the biggest factor in your amp’s sound, there are a number of other things that need to be done to keep your amp running optimally.

The most straightforward is making sure that the screws that hold the amp together remain tight. Because sound waves constantly shake your amplifier, screws have a tendency to wiggle loose. There are more than a few stories of an amplifier being ruined not by high voltage, but by simply falling apart in the middle of a performance.

To remedy this problem, tighten the screws on the outside of your amplifier up to the point that they feel snug and you have trouble going further. Don’t over tighten them, though: you could strip away the wood that the screw is drilled into and make the problem even worse.

Though tubes are the biggest factor in your amp’s sound, there are a number of other things that need to be done to keep your amp running optimally."

Another easy fix is scratchy pots. With the amp completely unplugged, take the knobs off your potentiometers and spray some contact cleaner into their front. Turn the dial full clockwise and full counterclockwise a few times and then rub away any excess contact cleaner. You can either do this for specific problem pots or just do all your pots at the same time. This will remove noise and prevent your signal from cutting in and out while you’re adjusting your tone.

Many people also replace their speakers to modify their tone, but sometimes speakers do blow out on their own. If you need a new speaker or want to upgrade, it’s a very simple process. You simply unplug the wires from the back of the speaker, unscrew any screws holding the speaker in place, and then move it out of the amp while taking caution not to bump anything else. Now simply reverse the process using a speaker of the same power rating: put it against the amp baffle, screw it into place, and attach the lead and ground wires coming from the amp.

Blown fuses can also be a result of bad tubes or indicative of a larger structural problem. If you blow a fuse, replace the fuses and turn on your amp again. If it continues to blow, there is likely an electrical problem with your amp that will need to be assessed by a professional.

Occasionally, an amp will need to have its filter caps replaced. These capacitors can store up high electrical voltages and are so dangerous that most amps house them under a special case to avoid people accidentally touching them. This is usually a job better left to the techs, since it requires quite a bit of knowhow to discharge lethal voltages from caps before replacing them.

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