I remember the excitement of buying my first guitar amp, determined to join the ranks of my favorite artists and play through a “tube” amp. Little did I know at the time the vacuum tube, or “valve” as it’s commonly known, had a rich history in the world of electronics.
Tube amps are classic pieces of equipment that most guitarists still use today. In this article, I will go over what precisely a tube amp is, the different types of vacuum tubes, and explain why these amps are preferred by most guitarists and bassists.
What is a tube amp?
Tube amps are guitar or bass amplifiers that use valves or tubes as the amplification source. This was the original technology used for guitar amps and remains the preferred amp type to this day. Tubes are used in various devices, and prior to digital technology, radios, TVs, and other sound-emitting devices used vacuum tubes.
The tubes in the amp essentially take the sound brought to it from the pickups in your instrument and amplify this sound to make it louder.
As early as 1904, tubes or electrical valves were used for functions such as signal amplification and current rectification in radios. Throughout the 1930s and 1940s, experiments with the technology continued to advance, but it wasn’t until the end of World War II and the explosion of consumer demand for televisions, radios, and recorded music that the true potential of the vacuum tube was realized.
During this time, guitars made the switch from acoustic to electric. Electric guitars required amplifiers to be played, so the tube amp became a staple for guitarists.
Pioneers like Les Paul and Muddy Waters pushed the limits of technology and created truly iconic sounds. It was an exciting time to be a part of the music world.
Check out my guide on how guitar amps work for more info on this.
Different types of tubes
Not all tubes are the same. The world of tubes is vast and intriguing, with a range of sizes and colors. They can be as small as diodes or as large as a car, but not all are suitable for use in guitar amplifiers. There are two main sections to a tube guitar amp: the preamp and the power output section. These sections of the amp require different types of tubes.
The pre-amp takes the weak high-impedance signal from a guitar and amplifies it to a stronger low-impedance signal to be sent to the power amp. The pre-amp also includes all the tone-shaping elements of the amp, bass-mid-high as well as gain and volume.
The power amp section takes the low-impedance signal from the preamp and amplifies it to a level that can drive a loudspeaker. The power amp section is also responsible for the final tone shaping of the sound by adjusting the output level and tone of the signal sent to the speaker. The preamp section is responsible for the tone of the sound and allows the musician to shape the sound to their liking, while the power amp section is responsible for the volume and overall power of the sound.
The 12AX7 is commonly used in the preamp section. While certain brands and years are more sought after, all 12AX7 tubes offer a good amount of gain and smooth compression, which is what many guitarists look for.
In the power amp section, many options are available, all of which depend on the desired volume and power output. Marshall, Orange, and Mesa Boogie amps all use the powerful EL34 pentode tube. These tubes can be pushed to their limits and are synonymous with the “British sound,” aggressive tones accentuating the mid-range. As guitar music evolved and bands began playing in larger venues, these tubes played a crucial role in ensuring the audience could hear the music being performed.
The Vox AC30 is a legendary amplifier known for its bright and distinctive sound. This is partly due to the use of EL84 tubes, which are smaller and more sensitive than their EL34 counterparts. This allows the AC30 to achieve a characteristic breakup and compression with minimal gain. While the sound of the AC30 can be divisive, the EL84 tubes are very bright! But it has been used on countless classic albums, cementing its place as a staple in the world of tube amplifiers. The Vox AC15C1 is another popular amp that uses these tubes. Check out my review of this popular amp for more information.
The 6L6 tube, introduced by RCA in the late 1930s, is a power output tube known for its warm, clean (did I say powerful?!) headroom. It was commonly used by Fender in their legendary line of amplifiers. Its even tone makes it a versatile choice for bands. A new industry emerged as guitarists began to use external effects pedals to simulate the overdriven tones of other amps.
The 6V6 tube, while smaller in comparison to the 6L6, offers a distinct tonal quality characterized by warm and rich tones. Despite its lower power output and tendency to break up at lower volumes, it is an excellent option for those who prefer a more subtle and nuanced sound and don’t always need to play at maximum volume.
In the mid-1960s, Marshall introduced the highly sought-after “Marshall Plexi” amplifier. They are expensive and difficult to find these days. The KT66 tube was a key component in its design, providing a unique warm tone with ample power and clean headroom, similar to the 6L6 tube.
So, what is a solid state amp?
The world of guitar amp manufacturing was bustling in the 1960s with the creation of various tube-based options. However, the technology behind them had not progressed much. By the time companies like Fender and Marshall began mass-producing these amplifiers, the military-industrial complex was already working to make the bulky, unreliable, and expensive tubes obsolete.
Enter the solid-state transistor. From a manufacturing standpoint, solid-state amplifiers were a dream come true. They could be quickly and inexpensively produced, with far fewer components required than tube amplifiers. In the late 1960s, Fender embraced this technology and began manufacturing solid-state amplifiers, presumably to make tubes a thing of the past.
However, this effort failed to catch on, they lacked the warmth and character of tube amps, and by 1971, Fender discontinued their solid-state line. Customers were hesitant to adopt the new technology, and it wasn’t until the 1980s that solid-state amplifiers became more widely accepted. Even so, they are still considered inferior to tube amplifiers and are often viewed as a more affordable option for beginners.
Why do guitarists prefer tube amps?
Tube amps have a distinct character and warmth that many guitar players appreciate. However, they do have some drawbacks, such as noise, tube failure, and cost. They are also known to be less reliable than solid-state amps and can require more repairs and maintenance. Despite these issues, many guitar players continue to use tube amps because of their unique tonal qualities and the way they interact with the guitar and pedals. Tubes can also be replaced, which can enhance the tonal quality of the amp and overall sound. Additionally, well-maintained tube amps can last for decades and even improve in tone over time.
Looking for a new guitar amp? Check out my guide for the best beginner amps.
How often do you need to replace amplifier tubes?
Amp tubes can last anywhere between 6 months to 5 years, depending on how much strain you put on them. The louder and longer you play out of your tube amps, the more likely you are to have to replace the tubes sooner.