Are Tubes Still Relevant to Today’s Audiophile? 

Vacuum tubes, historically speaking and consistent with what are used in today’s audio systems, were invented, according to most sources, in 1904 by John Ambrose Flemming. In 1907, New York inventor Lee de Forest patented a tube design similar to Flemming’s, except for an added electrode called a grid. Initially, tubes were used in the then state of the art communications technology, the telegraph. 

Flemming’s invention was called, not surprisingly, a Flemming Valve and, as he was an English physicist, the “valve” moniker became standard in England and throughout Europe. Here in the United States, the term “tube” is most commonly applied. Understand first the terms “valve” and “tube” both describe the same thing – a device utilizing thermionic release of electrons to facilitate both amplification and converting alternating current (AC) to direct current (DC). Even the identifier, or part number, may be listed one way in the U.S. and a different way in Europe – for the same tube, no less. 

Tubes reigned supreme in audio systems for almost the next 50 years. In December of 1947, everything changed when two scientists with Bell Laboratories, then a subsidiary of AT&T, shocked the world with the invention of the semiconductor transistor. Almost immediately, any electronic device, including radios, televisions, and even home stereo equipment, began the transition from requiring bulky, heat producing tubes to transistors and the integrated circuit. Suddenly, the audio system battle between tubes and solid state, along with the unanswerable question of which one is best, began. 

What Does a Vacuum Tube Do and What Are Its Parts?

In essence, a vacuum tube is an electrical device designed to, as it applies to high performance audio, amplify a signal – predominately in a power amp, but also in other components as well, invert the signal polarity where required and convert alternating current (AC) to direct current (DC). What a tube effectively does is control the current flow of electrons inside the tube itself. 

Without being overly technical and too lengthy, most tubes have very similar internal parts. Common to all amplification tubes is a filament. Filaments produce both heat and light. The glow you see on a high performance amplifier tube is created by the filament. This is also why tubes get so blazing hot. A tube with a filament with different colored lights is not really doing anything special. The light show does look really fascinating, however. Filaments are designed to create sufficient heat to assist with the production of electrons. The filament’s real purpose is to work in conjunction with the cathode. 

In tube components, the cathode is a vital part of how a tube works. When the filament gets hot, the negatively charged cathode, almost always in very close proximity to the filament, will be heated by the filament to a very high temperature. When a sufficient temperature has been achieved, the cathode begins to emit electrons. Because inside the tube itself is a vacuum, the electrons are free to move unimpeded, and will bang around with no destination. Something is needed to attract the electrons and force them to move in a manner intended to complete an electrical circuit. 

The anode carries a positive charge. Just as in magnets, positively  and negatively charged poles attract each other. This is what takes place when the negatively-charged cathode, heated by the filament, releases electrons and the positively-charged anode attracts these electrons. This flow from negative to positive actually functions like an electrical circuit, but only in one direction. Variable current flow is why the term “valve” was originally used. The flow of electrons creates an electrical circuit as long as there are electrons moving from the negative, or the cathode, to the positive, or the anode. This explains why high voltages are required in tube amplification. A lot of voltage is required for the filament to create sufficient heat to cause the cathode to emit electrons, which pass to the anode. This flow of electrons takes place because, just as in magnets, two forces with opposite polarity will attract each other. Likewise, similar poles will be repelled. 

Located in between the cathode and the anode is a charged piece of metal most commonly called a grid. The amp (or other type of component) is linked to the grid. The polarity of the grid changes from negative to positive. When the grid is negatively charged, the flow of electrons is reduced. When the grid carries a positive charge, the signal is accelerated, because opposite poles attract. Because the component is tied to the grid, the signal is increased and decreased, thereby affecting the operation of the component itself. 

In this respect, the tube is acting like a “valve,” increasing and decreasing the signal as the flow of electrons are varied. A continuous flow of electrons moving from the negative cathode to the positive anode ensures the signal is maintained. Describing a tube as a “valve” makes much more sense when it is understood how a tube actually controls the flow of electrons, just as a water spigot controls the flow of water. 

While not always used in tubed components, one element may be a rectifier, or more technically, a diode. Almost always used in conjunction with a transformer, a diode has the primary task of converting AC power from the wall outlet to DC, which is what power supplies and other related electrical circuits prefer. Sometimes, other internal electronic parts facilitate AC/DC conversion, which means that a diode, or rectifier tube, will not be used. This is a matter of design of the individual piece of audio gear. 

What Are Some Types of Tube Audiophile Gear and How Are They Different? 

One of the more common type of products using tubes is the Single End Triode Amp, or SET for short. SET amps are basically simple in their design and application. In a SET tube amp, one triode tube is used for each channel. Because of their design, SET amps are normally lower powered, commonly two to 20 watts per channel. They will work best with highly efficient speakers that do not need massive amounts of power. If you like a very warm, highly detailed presentation at lower volumes, a single ended triode, or SET amplifier, is a very wise choice. Any speaker system with low efficiency may not perform very well with a low powered SET type amp. Conversely, a highly efficient speaker paired with an SET amp may have the ability to play very loudly. I’ve heard three watt SET amps paired with efficient speakers play so loudly I almost had to leave the room. 

Any tube amp which provides substantial amplification, well beyond the range of a triode tube, comes in two versions: tetrode and pentode. While these types of tubes function in a similar manner to the more simplistic triode tube, tetrode and pentode tubes have a slightly different design to provide increased amounts of amplification. These type of amplification circuits are easily capable of 100 watts to 200 watts (sometimes even more) of output power per channel. Different brands of tubes may sound different and even cause increased levels of distortion. Some amps may even contain both tetrode and pentode tubes in the same device, and allow the user to switch between each one. 

What Are Some Modern Downsides of Using Tubes in an Audiophile System?

• Lots of heat is the most obvious place to start when talking about the downside of tubes. The high level of heat required for the thermionic release of electrons means the tubes will get very physically hot. When left on for long periods, such as long listening sessions, any tubed device may easily heat up the room, not to mention the component itself. This condition is compounded if there are multiple pieces of tubed gear – like an amp, preamp and phonostage.
• Generally speaking, tubed components use a lot of electricity. For those who are mindful of how much electricity a stereo system uses, tubed gear will almost always be more power consuming than solid state gear. This may lead to higher utility costs. Some tube amps have a bias feature, which allows the reduction of the power consumption and usually a lower operational level of heat. Bias may range from nearly zero percent of full power to 50 percent to 100 percent. Lower bias levels usually will also mean reduced sonics. Tube amps reportedly lose about 70 percent of the energy they draw from the wall to heat, thus they are anything but efficient in terms of cost and overall operation. 
• It is not advisable to leave tubes powdered on all the time. Because of the high levels of heat most tubes create, their lifespan is typically shortened when powered on for long periods of time. Essentially, the more they are in a power on state, the faster they will burn out and need to be replaced. Some tubes do last longer than others, but they all have a finite service life. Small triode tubes may last for about 10,000 hours. Larger tetrode and pentode tubes may last substantially less. Once tubes begin to fail, their sonic capability will begin to gradually suffer. So, if your tubed amp or other component suddenly begins to sound less glorious than normal, it is a pretty safe bet one or more tubes is on the short road to failure. 
• Tubes tend to be microphonic. This is a really wild condition whereby a tube will tend to act like a microphone and pick up external sounds. If a subwoofer or large floorstanding speakers are placed very close to a tube amp, the bass frequencies of the driver(s) may be picked up by the tube and transmitted as distortion. To test how much a device may be affected by this condition, set the volume at a minimal listening level, lightly tap on the component’s housing and listen for the tapping sound to come through the speakers. The louder the tapping sound is presented by the speaker, the more suspectable to microphonic effect your device will be. It is not advisable to tap on the tube itself. 
• Tubes are not available in a surplus status at the present time. This may change as time goes on, but there are not many manufacturers of tubes in the United States. Russia was once a source, but their production is not anywhere nearly as robust as it once was.  There are also tariffs over their attack on Ukraine, which make getting Russian tubes even more complicated these days. Other countries in Europe have been effective suppliers of tubes at one time or another. Think places like Poland and some of the other similar European countries. At the time this article was written, Ukraine was a major tube manufacturer and was a supply partner to audio companies all around the world. With the war with Russia, how long Ukraine will remain a significant player in tube production is unclear. In a perfect world, we wouldn’t have to deal with geopolitics in our audio systems, but we don’t live in anything close to a perfect world, thus these are our realities. 

What Are Some Modern Day Differences Between Tube Based Audiophile Gear and Solid State?

Now we get to the heart of the matter for the modern audiophile. Tube-based audiophile electronics can produce very realistic levels of clarity and accuracy. What most people call a “warm” sound is how an analog tubed device sounds more “natural” than a solid state circuit. With the advent of modern, Class-D semiconductor-based amps which create little to no heat, need almost no maintenance and draw minimal power from the wall, many audiophiles feel Class-D sonically rivals tubed gear without any of the downsides. 

Tubed gear uses distortion as a friend to achieve this characteristically “warm” sound. We’re talking harmonics here, specifically even ordered harmonics. Tube amps utilize second order distortion, which to most human brains sounds pleasing. And certainly, contrary to accepted audio norms, tubes are not as prone to clipping (overloading the amp) and consequently make better use of distortion than do solid state components.  It is not uncommon for a SET amp, for instance, to have very high levels of distortion, yet still sound magnificent. It is not advisable, therefore, to make choices based exclusively on distortion specs when considering an SET amp.  

Some designs are called “hybrid.” These devices use both an analog tube design, normally on the output stage, and a solid state circuit, normally on the input stage. This design intends to provide a best of all worlds. I once had a hybrid phonostage. The solid state input was powdered on all the time. When the power button was activated, the tube outputs would power on and the phonostage was ready for use. However, it did take an hour or more for both stages to reach thermal stability and produce the highest level of sonics. Normally, I would turn the phonostage on, leave the audio room and return in an hour or so, when everything was warmed up and ready to go. My current phonostage is completely solid state and remains in a constant power on state. Warm up is therefore not necessary. I will allow, however, tubes and LPs do seem to go together like cake and ice cream. 

Tubes also have an advantage in personalizing a pleasing sound. “Tube Rolling” is the practice of using a variety of different tubes by different manufacturers and even different designs, as long as they are the same type of tube overall. Trying a variety of tubes allows the user to find the most pleasing sound. It is very difficult to start swapping out transistors in a solid state amp. 

Another common concept in the audiophile tube world is “New Old Stock.” While they are decidedly difficult to find, the idea is discovering tubes that historically yielded significant levels of performance, but were made many years, even decades ago. If a supply of such tubes is found in the back of an electronics store, they may be dusty and the boxes faded. However, the tube is otherwise brand new and never used. These tubes are therefore termed “new old stock.” Finding a stash of “NOS” tubes is a rarity and, if found, better buy them all. 

How Does Tube Gear Match Up to New Solid State Amp Designs?

If solid state devices have done anything innovative, they have embraced a wide ranging design ethos. We now have Class-D amps which, to many audiophiles, sound far superior to multi decades old designs. New technologies, such as Gallium Nitride (GaN) amps, are combining affordability, light weight and, for an increasing number of amps, remarkable sonics which many feel rivals Class A and tube designs. Solid state amplifiers are available with other components, such as preamps, phonostages, DACs, and streaming devices all built into one housing. For that matter, a variety of solid state gear may be bundled into an all in one component, just like your personal insurance needs. One relevant question – does the convenience of all the new and innovative solid state designs outweigh the sonics a significant percentage of audiophiles prefer in choosing tubed gear? Given the vastness of all audio equipment choices, this is a pervasively difficult question to answer. 

Final Thoughts on Tubed Audio Equipment These Days …

Many solid state proponents today have the concerted opinion that solid-state audio gear has progressed to the point where it is sonically equal to analog tubed gear. The design of solid state equipment, the theory goes, has been constantly changing, and actually improving, while the basic functionality of tubed gear has remained essentially the same. Both of these positions have some level of associated truth. At the end of the listening session, so to speak, this entire debate boils down to one principal deciding factor – personal preference. Some people prefer the warmer, purportedly more natural sound of tubed equipment. Others, like myself, are firmly entrenched in the solid state camp. Still others like to mix and match. 

For tube aficionados, it will be a very difficult task to diminish the level of devotion to these types of enthusiast audiophile components. They will forever rejoice in the sound of their tubed amp, preamp,phonostage and any other related devices. They are not interested in what those who champion solid state believe, or the equipment they support and purchase. Considering tubes are at least a 100 year old technology, this level of devotion certainly speaks to the attractiveness of such a timeless component design. Deciding on whether a tubed piece of audio gear is the correct choice is only provable by one predominant task – listening. This may not be a welcome practice, but one that is necessary. How will any audiophile be able to decide if they enjoy a tubed component if they do not hear it for themselves? Answer – they can’t. 

Just as someone may like chocolate ice cream, others like vanilla, some like Ford and others love themselves a nice Chevy.  Personal preferences are our guiding principle in whether we like the sound of one audio technology over another. Tube amps are old-school but, just like a powerful muscle car from the early 1970s, there is an appeal to the time-tested, musically engaging technology of tubes, despite all their real-world downsides. Are today’s electronics better? Just in the past few years, the delta in performance from tubes to Class-D switching amps, as well as Class-A amps, has narrowed dramatically. For most people, these new technologies are going to be more compelling, but let’s not forget about the allure of tubes. They produce a sonic magic which not only will warm your listening room, but they can also warm your heart with a level of sonics many feel is unequaled.