It might seem like a simple thing to plug an electric guitar into an amplifier and play, but there’s a lot that goes on in-between the strings and the sound, and much of it happens inside the amplifier.
Filled with electronics and parts most of us have only seen in pictures on the internet, it can be a bit technical and confusing to understand the inner-workings of an amplifier. But luckily, you don’t need to know everything. In fact, we can simplify everything quite a bit like this:
There are two main types of amplifiers, tube amps and digital amps. Tube amps came first and feature original, old school, analog made tone, while digital amps are newer, and use all-digital tone which often recreates the sounds of tube amps.
Much of the greatest sounds in rock history come from a tube amp. Your favorite guitarist likely uses a tube amp, especially if he was around before the new millennium. Though digital amps are very common nowadays and there are plenty of great digital amps which model those tube tones almost indistinguishably, there’s something special about the real deal—and it all comes from the tubes.
Tube amplifiers (sometimes known as valve amplifiers) use vacuum tubes to power the sound. Vacuum tubes are sealed glass bottles with all of the air removed, which look a lot like lightbulbs. They consist of a cathode, a grid, and a plate. The cathode is on one side and the plate is on the other, with the grid in between them. When an amp is turned on, filament within the amplifier is heated to warm the cathode and charge the plate. Once heated, the negatively charged cathode emits electrons which are attracted to the positively charged plate. The grid in between them influences this flow by repelling certain amounts of electrons or allowing them to pass.
When you pluck a string on your guitar, it vibrates within the magnetic field of the pickup and produces a very small electro-magnetic charge. This little charge travels as current through the guitar’s controls, down the cable, and into the amp. The current is applied to the grid which in turn regulates the electrons flowing from the cathode to the plate and amplifies the signal. The amplified signal flows through the plate, is directed to the output transformer, and from there goes out the speaker.
Tube amplifiers consist of a few different types of tubes, including rectifier, preamp, and power tubes, which all function in a distinct way inside the amp. Rectifier tubes convert AC electricity from an outlet to DC electricity, which is required to power the preamp and power amp tubes. The primary function of a preamp tube is to shape and condition the overall tonal characteristics of the incoming signal (i.e. distortion or overdrive). Power amp tubes control the overall output of the amplifier.
The power and preamp tubes work together to create the guitar’s tone. You can hit a preamp tube with a large current, such as from a pedal or an active pickup, and create richer harmonics, distortion, and sustain. This is considered the first ‘gain’ stage. Some amps can contain 2, 3, and even 4 gain stages. This is sometimes called having ‘cascading’ gain stages. The signal then goes to the power tubes for final amplification.
5AR4 Rectifier Tubes
. The rectifier tube converts AC electricity from an outlet to DC electricity which your tube amp requires to power the preamp and power tubes. Until recently, only older amps would have used a tube rectifier. Beginning in the 1960sand on most amps used solid state rectifiers as amps got bigger and louder. Solid state rectifiers are generally more efficient and suitable to higher voltages.
However, the tube rectifier provides a certain ‘feel’ that many guitarists prefer. Since this tube acts as a power supply for the other tubes, it can ‘sag’ when the demand for power is great, as in when the strings are picked hard and with higher intensity. This old-school technology still plays an important part in today’s guitar tones.
The 5AR4 (aka GZ34) rectifier tube is the most widely used model today. It can be found in many new Fender reissue amps such as the Deluxe Reverb, Princeton and Super Reverb. Vox AC30, Marshall JTM 45 and Bluesbreaker combos also use them.
12AX7 (ECC83) Preamp Tube
The 12AX7, also known as ECC83, was first developed and produced in 1947 by RCA. It is currently made by a variety of companies such as New Sensor in Russia (Electro Harmonix, Sovtek, Tungsol and other brands), JJ Electronic in Slovakia and Shuguang in China. Total annual production is over 2 million units. It is a vital component in a tube amplifier. Virtually every Fender, Marshall, Mesa Boogie, Vox, Peavey and other tube amp has at least one, and as many as five, 12AX7 preamp tubes. It offers a wide range of versatile tones, whether it be a sparkling, clean twang to a mellow bluesy tone to a raging, metal assault and all points in between, depending on how the amp is designed and how many gain stages it features.
The 6L6 tube was first introduced by RCA in 1936. This tube very quickly became the most widely used tube for many applications in all industries.
Currently, the 6L6 is produced by all the major tube companies including New Sensor, JJ Electronic and Shuguang. It is available by all the brand names such as JJ, Sovtek, Tung Sol, Electro Harmonix, Groove Tubes and others.
In guitar amps, the 6L6 was most often used in high-powered amps such as the Fender Twin Reverb, Fender Dual Showman and others that deliver loud, glassy clean tones. The first Marshall amps, JTM-45 head and Bluesbreaker combo, also used 6L6 power tubes. A young Eric Clapton can be heard using the Bluesbreaker on the “Beano” album by John Mayall. It’s used in workhorse amps like the Fender Hot Rod Deluxe and Hot Rod Deville. Today the 6L6 is also prized for its crunchy overdrive tones, with strong highs, smooth mids and strong, and tight bottom. Mesa Boogie and Peavey use the 6L6 in many of their high gain rock amplifiers.
The 6V6 tube was first introduced by Ken-Rad Tube & Lamp Corp. in late 1936. It was a very sturdy tube and widely used for military applications.
Currently, the 6V6 is produced by all the major tube companies including New Sensor, JJ Electronic and Shuguang. It is available by all the brand names such as JJ, Sovtek, Tung Sol, Electro Harmonix, Groove Tubes and others.
In the 50’s and 60’s the 6V6 was widely used in mid-power amps, most notably by Fender and Gibson. Also used in classic Magnatone, Silvertone and Supro amps.
The 6V6 has a sweet tone at low levels but is even nicer when overdriven to max output. 6V6 amps are popular for recording, most famously used in Fender Tweed Champs and the Fender Deluxe series, starting in the 50s and running straight through today with the Deluxe Reverb reissue combos. The Deluxe can be heard on many famous records, including “Revolver” by the Beatles, “The Royal Scam” by Steely Dan and many classic Allman Brothers records.
The EL34 tube was first introduced by Phillips in 1949. Starting in the 60s, the EL34 became associated with the “British Tone” and was widely used by companies such as Marshall, Hiwatt and Orange. It was also very popular in high powered hifi amps such as the Dynaco Stereo 70.
Currently, the EL34 is produced by all the major tube companies including New Sensor, JJ Electronic and Shuguang. It is available by all the brand names such as JJ, Sovtek, Tung Sol, Electro Harmonix, Groove Tubes and others.
The EL34 tends to overdrive at lower volumes than other power tubes. It also has a ‘sweeter’ midrange response than for instance a 6L6 and has provided the classic lead guitar tone of legendary guitarists like Jimi Hendrix, Jimmy Page, Pete Townsend, Angus Young, Ritchie Blackmore, Gary Moore and many, many more. To this day, a wall of Marshall or Hiwatt stacks, all loaded with EL34s, remains one of the most enduring images of rock’n’roll.
The EL84 tube was developed and introduced by Phillips in 1953. It came to prominence when it was used in Watkins (WEM) and Vox amps preferred by the British Invasion bands of the 1960s.
Currently, the EL84 is produced by all the major tube companies including New Sensor, JJ Electronic and Shuguang. It is available by all the brand names such as JJ, Sovtek, Tung Sol, Electro Harmonix, Groove Tubes and others.
The EL84 is probably most well known for its use in the Vox AC30. Notable users of this legendary amp include Brian May, Rory Gallagher, Mike Campbell, the Beatles and even Ritchie Blackmore on ‘Machine Head’ by Deep Purple.
The EL84 offers a nice, lightly compressed and smooth overdrive tone with plenty of high end sparkle and chime. Still popular in the AC30, it is a favorite power tube choice for modern boutique amp builders. It is also used in workhorse amps like the Fender Blues Jr. and Peavey Classic 30.
The KT66 tube was introduced by Marconi-Osram Valve Co. in 1937. In design it is very similar to the 6L6. KT66 tubes generally have thicker glass and are wider and taller than 6L6 tubes. While they work in any amp designed for a 6L6 (if it fits), the KT66 draws more current from the heater. It is a good idea to check with an amp tech to make sure your amp can handle the extra draw.
The tone is often described as “big” compared to a 6L6. Open and dynamic with little compression and smooth, singing sustain when pushed hard. Also, this tube is more robust than most.
The KT88 tube was introduced by MO Valve Co. in 1956 as a larger variant of the KT66. It is still considered one of the best sounding power tubes for hifi audio amplifiers.
KT88 tubes are currently made by New Sensor, JJ and Shuguang.
Marshall used them in their 200 watt Marshall Major amps. KT88’s were also used in Hiwatt Custom 200 and 400 bass amps. They can be used as a substitute for 6550 or even EL34 tubes, if you’re looking for tighter, cleaner tone with less distortion.
The 6550 tube was introduced by Tung Sol in 1955. Based on a 6L6, it was designed to have more output and durability.
The 6550 is currently only made at the JJ and New Sensor factories.
The 6550 has lots of dynamic headroom and never really distorts or even sounds dirty, no matter how hard it is pushed. From the early 70s on it was used by Ampeg in the legendary SVT series of amps. The back line of the Rolling Stones consisted of a wall of SVTs both for guitar and bass, all powered by 6550 tubes. The 6550 was also common to all Marshall amps sold in the U.S. in the 80s. Lots of JCM800 and JMP’s had the tubes.
Certain Ampeg amps such as the VT22, V4, V4B and others can be converted to use the 6550 instead of the original, but obsolete 7027 power tube.
If you are looking for these or many other tubes, Sam Ash Music is the place to go. We proudly carry all of the above tubes and so many more by Tungsol, Electro-Harmonix, Sovtek, Groove Tubes, JJ, Tenalex, and other brands. Visit us at any of our locations around the country, or call us at 800-472-6274 or visit samash.com. Our expert musicians are waiting to help.