Beginner’s Guide to Vacuum Tube Amplifiers
If you’re into audio, there’s no doubt you’ve probably been involved with, or at least overheard, a debate about tube amplifiers. If you’re looking for a way to catch up on vacuum tube amplifier basics, we’ve got tube amps explained for you here.
What Is A Tube Amp?
Tube amps, or valve amps, are a type of electronic amplifier. As the name hints, they use vacuum tubes to increase the amplitude, or the power of the input signal. While they still have a massive following, low and medium power valve amps were largely traded out for solid state amps during the 1970s because of reliability and maintenance.
Difference Between Tubes & Solid State
While a solid state amp uses electronics, like diodes and transistors, to amplify the signal, valve amps use one or more vacuum tubes. On paper, this would yield the same results if you have two amps consuming the same amount of power, but the difference in sound and tonal quality is very noticeable—even to a person who has no background in music or audio.
Now, amps do not come down to being solid state or valve. In fact, there are many amp models that are “hybrids” and use both tubes and electronics to produce a nice sound. While hybrids often employ vacuum tubes in the tone shaping circuitry, the power section uses solid state electronics. As far as response and warmth, hybrids are closer to full valve amps. However, audiophiles and purists will be able to decipher differences among the different types of tube amps.
Vacuum Tubes vs Solid State: Which Is Better?
When it comes down to the long-time argument of which kind of amp actually sounds better, it’s all a matter of personal preference. However, there are a few factual considerations to take into account. Like, for instance, the fact that solid state amps generally require less maintenance and tend to be more reliable. They are also less delicate than tube amps as they are, after all, solid state without tubes that can be broken or blown.
If you’re like many and you’re stuck on the warmth and responsiveness of a tube amp, you have a few options. First, if you don’t want to deal with the weight and maintenance of a tube amp, modeling amps have entered the scene in recent years—emulating not only the sound and tonal qualities of a valve amp, but typically “modeling” the qualities of a specific tube amp model. Now, some modeling amps are better than others and typically there’s a “sweet spot” in the volume range where the modeling amp sounds at its best, but it is an option to consider that tends to be a bit more cost effective.
If you’re after an authentic tube amp, however, keep in mind that size is not the determining factor. Tube amps usually sound their best when fully cranked and all the tubes are saturated. A little amp will put out plenty of volume at the top of its range, whereas a large tube amp (such as a half-stack) will likely blow out your ear drums if you take it up past five. But, determining how big of an amp you need comes down to the space you’re going to be using it in.
Construction: A Deeper Look
At the most elementary level, tube and solid-state amps are the same. All of them have a chassis, electric parts, and an enclosure. The significant difference is in the details.
Tube amplifiers use a high voltage DC pathway to generate amplification and take a much lower level AC music signal. This mix of AC and DC necessitates using addition elements to isolate potentially lethal voltages in the user along with the equipment.
To deliver their potential, tubes require high voltage. Solid-state devices generally don’t require high voltage so their power supplies are much easier and much cheaper to create. The two solid-State and Tube amps have power transformers to operate their electricity supplies.
Tube amps generally lift the incoming voltage, rectify it, clean it and send it to the circuit in different voltages, from 6 volts to 500 volts. The greatest voltages at a Solid-state amp typically come from the output devices that push the speakers.
While we’re on the topic of output devices, let us look at the #2 most significant difference between solid-state and tube amps. Solid-state amps do not need an output transformer.
High voltage vacuum tubes have a high output impedance and require a transformer to decouple the high voltage DC in the much lower power AC music signal delivered to the speakers. Speakers won’t run on DC, they will melt.
The output Transformer also changes the high impedance signal of several thousands of ohms to a low impedance signal in the 2 to 16 ohm range to coincide with the speakers you join. The transformers are the most expensive components in almost any amplifier. By removing a transformer, solid-state gets a massive cost advantage.
Tube amps require vacuum tubes which impacts the whole design and construction process. Tubes are electro-mechanical devices that operate on high voltage and make a good deal of wasted energy in the kind of heat. High voltages of varying amounts feeds different elements inside the tube to direct the flow of the cloud, though a little AC control voltage modulates the flow volume. Therefore, the British word, valve. This procedure creates heat in vacuum tubes, which could be 200 degrees celsius. Therefore, the enclosure for a tube amp has particular requirements for security, to protect the consumer and innocent passersby.
As scientific study improved, using a mix of dissimilar components combined on silicon wafers to make voltage amplification occurred. Most contractors of vacuum tube gear, seen solid-state apparatus as a threat to their business or a chance to boost their bottom line if they altered their designs.
Since solid-state construction can be smaller, lighter and less costly the removal of the vacuum tube appeared to make sense. This opened the door to mass manufacturing and printed circuit boards.
Early printed circuit boards simply eliminated the mounting points for components and the wires that combined them. Components were soldered into the boards by hand.
Modern solid-state amp structure is typically done on multi-layered printed circuit boards. The components are set up by robots and then soldered in an automatic procedure called wave soldering. The principal purpose is to create them fast and economical by eliminating work done by men and women. You may get much greater quality solid-state amplifiers but the cost rises quickly in the event you require higher quality.
Some guitar amp builders are still using non-conductive part cards with eyelets or turrets to mount their parts. This is ideal for vacuum tubes but not so much for solid-state.
If you’re in need of some visuals at this point, take a look at this quick 4-minute video that does a great job explaining the physics:
Are Tube Amps More Expensive?
When it comes to price, solid-state amplification really shines. Things like transistors, FET’s, rectifiers and integrated circuits are all machine made in enormous quantities using high-speed assembly lines. This reduces the purchase price of individual components to pennies. As most designs do not use an output transformer there is a massive saving on that one item.
After purchase, solid-state amps have almost no ongoing maintenance costs. They run cool, unaffected by vibration and will operate for days without a care. Struggling in solid-state amps usually occurs very early in their life span, due to manufacturing defects.
Vacuum tubes on the other hand, require a whole lot of manual labour and are made in relatively small batches, which makes their cost to produce hundreds of times higher than equal solid-state devices. The average tube amp has ongoing maintenance costs. Tubes are fragile and subjected to intense cycles of heating and cooling. Vibration and heat will degrade tubes and they’re susceptible to developing stray noise and microphonics.
Tube replacement is inevitable and in the case of power tubes, technical skills are required to ensure the amp is correctly set up for proper, safe, operation. Most people do not have the skills to work safely on high voltage equipment like a tube amp, and must hire somebody to do this job for them.
Both solid-state and vacuum tube amplifiers are available as both cheap consumer products and quite expensive professional grade equipment. After purchase, tubes will cost more to use.
What Makes Tube Amp Tone So Special?
Within the group of music enthusiasts that really care about their sound, there are those that think vacuum tubes simply sound better and the ones that think solid-state is just as good or better. Solid-state fans can provide highly technical information that supports their argument, as can those that favor tube layouts.
Amps are basically in two groups: Those designed to create music and those designed to reproduce music. Both utilize completely different audio sources as inputs and very different speakers to handle the output. Musicians want amps that can provide a wide range audio, from sparkling clean to highly distorted and harmonic laden.
Home audio enthusiasts want amps that will replicate the original source material as closely as it can. They do not want to create distortion, they want to replicate the distortion made by others.
Distortion is one of the main selling points for tube amp fans. Solid-state amps do not appear to distort as musically as vacuum tube designs. The primary reason is that when you push tubes hard the distortion comes on slowly and presents itself as gradual compression which blooms into distortion. The high voltage provided to vacuum tubes ensures that the output of the device seldom exceeds the voltage that runs it. Solid-state amps utilize lower voltage supply rails to operate and the output signal can exceed the supply voltage. When that happens, they do not start to compress and slowly clip. They just cut off the output signal at that level. Sine waves become square waves immediately and the sound is not pleasant. That’s perhaps not the best for musical instruments and totally unsuitable for home audio enthusiasts.
However, the principal distinction is even-order versus odd-order harmonic distortion. Perhaps a lesser known sort of distortion, harmonic distortion of tubes is that which fills out the sound and adds heat.
Without becoming too technical, all amplifiers will have sympathetic distortion regarding the original signal. Tubes have largely even-order harmonics (known as second, fourth, and sixth). Solid-state apparatus have more odd-order harmonics (third, fifth etc). It’s the even-order harmonics that will give positive embellishments to the original signal, which makes it sound fuller. This is largely what offers the “tubey” sound, the full, deep, warm sound tube amplifiers are famous for. The odd-order harmonics made by solid-state amplifiers create a edgy or cut-off sound. Often this is seen as more “accurate” sounding, but the truth is it’s also largely the reason behind listener fatigue. It’s not natural distortion or an increase to the original signal positively, and great ears will tire of it quickly.
Solid-state does not seem to handle peaks or transients from the music signal as well as tubes. Essentially, I am talking about sound that goes bang or thump. This is probably due to that fact that tubes naturally have soft clipping and compression to handle transients and smooth those peaks and valleys.
A tube amp designed specifically for low frequencies requires a lot of output tubes and massive transformers to generate the energy that many bassists demand for live performance. This makes them very hot, very large and very heavy. The Ampeg SVT is widely considered king of the bass tube amps but it only delivers 300 watts while contemporary solid-state audio systems can deliver thousands of watts in a much smaller, cooler bundle by using advanced operating modes like class D.
If you are a skeptic, you should take a look at the direction taken by producers of solid-state guitar amps. The advertisements usually feature real tube tone as a major selling point. To be able to deliver on this selling point added solid-state apparatus were developed that more closely mimic the clipping characteristic of tubes. Helper circuits create things like asymmetrical clipping and distortion on demand, using simple diodes. The technology has actually gotten good over time. The debut of amplifier modelling is perhaps the biggest opportunity for solid-state amps to sound like tube amps and has been a real bonus for recording applications.
However, there’s a cost associated when manufacturers produce proprietary devices and circuits to emulate the sound of tubes. After the item stops production, any proprietary parts also cease production. Most popular tube amps are variants of circuits which have existed for more than 60 years and utilize a standard range of components.
In their glory days, producers of tube equipment did use oddball tubes to fit their designs and now you will occasionally find amps that use tubes no longer in production. Most currently produced tube gear uses standard, popular, vacuum tubes in their structure. There’s not enough sales volume to justify the production of new tubes because of their high production cost.
For those who have a tube amp today, you are likely going to be able to get replacement tubes in the future. What happens when your modelling amp loses its CPU? Are they still making it?
When it comes to modification there is nothing better than a tube amp. This starts you down the road to the land of tube rolling. The quest for a tube that sounds different or better than the one you used prior to it.
Many folks consider tube rolling to be among the best reason to own a tube amp. They’re on a quest for the best sound and tube rolling feeds the need. Output tubes do need some tech chops to substitute if they are using a fixed bias scheme. By way of example, a 6L6GC would appear the same from tube to tube. Because they are made by hand, a lot of variation is introduced because of differences in the spacing and orientation of the tube elements. If you should grab a random assortment of those tubes and install them, each would function differently in the circuit. Some might run too cold and some may run too hot. The bias voltage has to be set to compensate for the variations and find the output tubes running in the desired operating current. If you know how to use an electrical multi meter and a screwdriver, you can probably bias the amp yourself.
Looking for more info on tube rolling? We have a comprehensive tube rolling guide here.
If you wish to tweak a solid-state amp, you must open it up. Advanced solid-state circuits are more complicated and easier to destroy than tube circuits since they have a very low fault tolerance. Simple static electricity can kill solid-state apparatus, as can the warmth from an improperly used soldering iron. If you want to tweak a solid-state amp, you will need a qualified technician to do so. Tubes fit into a socket just one way, while solid-state devices are easy to install improperly should you not know what you are doing.
We’re talking about amps here, so you probably want to give this all a listen! This is one of my favorite comparison videos, take a quick four minutes of your time to check out this video:
Common Questions About Tube Amps
There are plenty of questions out there on the topic of tube amps, but here’s an overview of the most common.
Are They Louder?
One of the most common questions asked about tube amps is, “Are they louder than solid state amps?” But, the answer is less straightforward than most people would think.
If you set a power meter on the output of a tube amplifier and a solid state amplifier which were matched for complete output power, then the meter will read almost precisely the same power for equal drive requirements – so in this way, the answer is no, they’re not louder. But if you LISTEN to the 2 amps, you’ll realize that the tube amp does really sound louder to your ears, in opposition to what the meter is telling you. Why? It is tied up in the sensing tool—that is, your ear. The way the human ear functions is that it’s extremely sensitive to the harmonic content of a noise. A tube amp is not as linear (that is, has more distortion) at signal levels under clipping compared to a solid state amplifier.
The distortion increases gradually, and then more quickly as the amp starts to clip. In actuality, the distortion increases so slowly and is of such a benign nature that the onset of audible distortion doesn’t have easily defined threshold. It’s almost perfectly non-distorting right up to the point that it clips, and then it clips HARD. It’s easy to listen to the threshold. This abrupt onset of distortion can also be composed of comparatively harsh sounding distortion, not like the subtle second and third harmonics of the tube amp. In effect, the tube amp fools the ear into believing that its premature distortion is much louder. They, therefore, sound louder than what the actual meter reads.
What Is “Standby”?
It was initially a way to cut down on the wear and tear of the tubes, which would otherwise be continuously wearing out while they stood idle. Frequently, you will want to leave an amplifier without hearing any sounds, like during a rest between sets. The standby switch guarantees that the amp will be silent, and that the primary power source is disengaged from at least the electricity output part of the amplifier. This makes tubes last longer.
What Is The Proper Way To Power On and Off?
Turn the standby switch on (that is, to the standby position), then turn the power switch on. Wait about 30 seconds and then flip the standby switch to “play”. This guarantees that the heaters in the tubes are all heated up and that the startup stress level is as low as you can make it.
To turn it off, do not mess with the standby, simply turn the power switch off. That cuts both the primary power supply and the heater power, so it all simply stops and cools off. The hot tube filaments allow the tubes to continue sucking current out of the power supply filter caps so the caps are largely drained of dangerous voltages.
How Often Do Tubes Need To Be Replaced?
The simple answer is to replace them when they start sounding bad. This can be as short as six months or even after a year of regular gigging if you are cautious with the amp, or as long as several years to a decade of bedroom practice. Generally, the preamp tubes will last even longer.