Tube amplifiers sound better for many reasons known to musicians and truly dedicated music lovers. Starting from the euphonic distortions they add to the music, optimum sound at optimum levels, soft clipping, or less negative feedback. These effects may seem subtle, but they actually make a noticeable difference.
Digitalization has not made them less relevant, tube amps are still very popular. Professional studio microphones have been using tube pre-preamplifiers for many years now. Nowadays, the mics’ outputs are fed to tube preamplifiers before being digitized for recording and mixing.
Simply put, they make the music sound better.
But, can tube amplifiers hurt you? Or even kill you? How can you handle and troubleshoot your amplifier safely?
Tubes do get hot, but in an adequately operating and closed amp, they’re as safe as solid-state. However, it’s the inside of the amp that you should be concerned with as tubes run at deadly voltages. There’s more danger in working on them, but you can handle it on your own providing you’re experienced and careful.
In this article, we cover the basics of tube amps and the potential dangers of using them, along with useful tips for care and feeding of tube amps.
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What You Need to Know About Tube Amps
Pure tube tone in a guitar amp is definitely something you’ll opt for when deciding between tube amps and solid-state amps. Especially if you’re in a large room with good acoustics. It doesn’t mean they’re better than solid-state amplifiers, though. It’s how they’re different from solid-state amps.
Tube amps sound different (and better for many) because of euphonic distortions. They are more fragile compared to solid-state amps.
Known as a second-order harmonic distortion, it means that any given note you produce also produces a distortion an octave above that note. It is also true for higher-order even harmonics – the same note more octaves above.
This is certainly not the kind of distortion you’ll find in hard rock or metal. However, it adds certain fulness to your tone. And it’s inherent to tube amplifiers, where it happens naturally.
Tube amp distortion is harmonious, it also increases with things getting louder, just like in a musical performance. More harmonic content is generated when you play instruments louder or hit a piano key more. Reversely, the percentage of harmonic content decreases when the notes decay.
This is exactly what tube amps mimic. Like the Woo Audio WA7 Fireflies. It can increase its distortion directly with output level across three decades of voltage, or a power range of million-to-one.
Tube amps have the least distortion at the lowest levels, much like human ears or musical instruments. Accordingly, they can sound awesome if you play softly. Unlike, transistor amps you need to turn up to produce the best sound.
Optimum Sound at Optimum Levels
The thing about tube amps is that they sound great at the volumes at which you actually want to enjoy them. Both digital systems and solid-state amplifiers have the worst outcomes at low levels. Conversely, they perform best at close to their maximum output levels. It’s where no one actually plays them.
Most people enjoy music at about 1mW ~ 1W long-term RMS, or about 0.01W ~ 10W peak. That’s for use with normal music at normal levels. It means a 30 WPC amplifier is the right choice for most applications.
However, most sources publishing lab results typically plot performance down to 100mW. And the critical power range at which we enjoy most amps is from 1mW to 1W. It’s what happens below 100mW that actually matters the most.
So, if you’re going for a 100 WPC amplifier, it’ll be a good fit for a wide dynamic range of classical music at concert-hall volume.
Optimum Power Output
Unlike solid-state amps, tube amps are commonly rated for the power you actually need and will use. Like 8 to 80 W per channel. On the other hand, solid-state amps are typically rated up to dangerous power levels, like 300 WPC or 300W that will blow any single speaker.
Moreover, you’ll wind up paying huge sums for solid-state amps and the sound will be much worse at normal levels at which you will actually enjoy them.
Solid state amps have quite a definite clipping point. On the flip side, tube amps overload gradually. You can add more input for more distortion, but there’s no precise clipping point.
Negative Feedback & High Output Impedances
Given that they have more linear transfer functions than transistors, tube amps typically need and use much less negative feedback. This may not be necessarily negative. It’s the poor basic amplifier linearity that requires a lot of negative feedback to test well.
Amps needing a lot of feedback to cover up their basic flaws have a distortion curve that increases with frequency. And also have low output source impedances (high damping factors). Contrarily, tube power amps have higher output source impedances – lower damping factors. This is due to their lower negative feedback and output transformers.
When connected to a real loudspeaker, the lower damping factor changes the frequency and transient response of the system.
Tube amps are also safe for speakers and have completely isolated outputs. They also have some form of microphonics, which means that you’ll have an audible output each time you tap the amplifier. Despite the enormous growth of transistors, tube amps are a rediscovered way to make your music sound better.
Advantages and Disadvantages of Tube Amps
To understand whether tube amps are actually worth it, here’s the list of advantages and disadvantages.
- Always warmed up and ready to amplify the signal.
- Harmonic distortion
- For Class A amps, you don’t need to wake them up from a ready state.
- Smooth compression.
- Less headroom.
- Higher responsiveness to the touch
- Some Class A amps emphasize high order harmonics, which make them “sing.”
- Keeping them warmed ready requires more current, which results in shorter tube life.
- They require a fairly large room – not suited to living room practice or a coffee club
- They require more maintenance than solid state amps.
- They tend to cost & weigh more than solid state amps.
- They measure poorly in the lab mainly due to added distortions, but it’s the distortions that actually make them sound better.
Tube Amp Maintenance
Tube amps, as well as a large number of solid-state amps contain high voltages. Similar to other potentially dangerous objects, you should handle them with care. It doesn’t mean you should fear them.
You can replace mains fuses and swap tubes if you unplug the amp and screw in the chassis. Being intended to be replaced by the user, you can access fuses and tubes from the chassis.
However, you should be cautious and watch for indicators of something being seriously wrong. If there’s a chance the circuit may be damaged or the amp smells like it’s burning, you should contact a professional.
This includes arcing, fire, burning smells, or physical damage, like loose transformers or smashed chassis.
To troubleshoot the amp on your own, you need at least some level of previous experience.
You should troubleshoot the amp – replace the tube or the external mains fuse – only while it is unplugged. The only time you need it powered up is when you perform a test.
Based on the amp design, you may need to replace the good tubes every 3 to 5 years. Yet, it’s been reported that some tube amps were left on constantly for decades.
Dangers of Using Tube Amps
Tube amps can get hot. Given the fact that they work on the principle of thermionic emission, they need to get hot to be able to function. However, it’s one of the oldest (and tried) electrical technologies in use, there are almost no safety concerns.
Tube amps don’t explode. Since they’re in a vacuum, they can only implode. And that is unlikely to happen, given that you need to smash, drop, or deliberately implode them.
However, you should be aware that the power caps for tubes are rated 450 V and up, meaning they charge over 600 V. It may not be enough to kill you (although it can), but they can certainly hurt you. So, you should avoid dealing with them if you don’t have previous experience and knowledge of power circuits.
Finally, we recommend not leaving them for years. It’s not only the tubes that wear out but capacitors and resistors, as well, which may result in transformer failure. So, turn it off if you’re not using it.
Tips for Tube Amp Care
- Warm up your amp before use – at least, a couple of minutes before switching on the standby.
- Always replace the whole set of output tubes, ideally with those of the same make. Make sure the pins on the base of the tube are aligned correctly and the tube base fits on the amplifier perfectly.
- You should allow the amp to cool down before moving it.
- Make sure your cable is connected to your cabinet before connecting it to the amp. In that manner, you’ll never put a short on the output of your amp. It’s the same with signal lines. You should plug the cable into the source before plugging the other end into the amp.
- Don’t store your amp in damp or overly humid places. The same goes for the speakers.
- Make sure your amp has the correct impedance matched to the cabinets. It means you should avoid loading the amp down with too low an impedance by connecting too many speakers in parallel.
- Ultimately, tube amps may not be resistant to physical damage (hits or smashes), even if in a padded case.