Valve types explained

If you talk to any guitarist you will undoubtably hear the world ‘valve’ or ‘tube’ thrown around. The sound of a valve amp cranked nice and loud is synonymous with rock and guitar heritage. Valve technology was predominately found in televisions and radios from the mid to the late 20th Century, transistor technology advanced and took its place. That being said, guitar amplifiers remained married to valves due to the unique feel and tone they produce.

To simplify very complex technology, a guitar amplifier ‘amplifies’ a signal from a guitar pickup through its preamp and power amp stages.

Similar to the construction of an old-fashioned lightbulb, a valve is a collection of different elements together in a vacuum, cased in a glass cover. One of the elements, the Cathode, is heated and electrons (electricity) flow from this end to the high voltage Anode on the other end. Another element, called the ‘grid’, controls the flow of electrons from the heated end to the high voltage end. It’s that fact that makes it an amplifier – wiggle the grid and a much larger flow changes amplification.

Incidentally, it’s the addition of the grid to the Cathode (heated element) and the Anode (high voltage element) that makes a Triode amplifier (Tri – three). With just the Cathode and Anode this would be a Diode amplifier (Di – two).

Preamps are the smaller-sized valves inside your amp. The preamp adds almost all of the “voltage gain” and the power amp multiplies the voltage gain with “current gain”. Voltage x current = power, hence the phrase ‘power amp’. The relationship between preamp, power amp and every component in-between can make a huge difference in your tone. Below we go through some of the most commonly used power amp valve types and how they lend themselves to different tones.

Valve types

EL34

EL34

Still used in many amps that Marshall produces today, the EL34 is a Marshall favourite, when creating the first Marshall amplifiers these were used in the place of the 6L6. The EL34 is a pentode, and the extra element (suppressor) reduces any losses in the valve. The EL34 provided unique secondary harmonics and a warm mid-range that eventually became the iconic, distorted Marshall sound.

EL84

Seen as the smaller-sized sibling to the EL34, the EL84 provides quick breakup and a higher, brighter sound.

6L6 and 6V6

Synonymous with US-made amplifiers, the 6L6 is commonly used for ‘clean’ guitar amplifiers. Offering a bright, chimey sound.

Similar to the EL34/EL84 relationship, the 6V6 is similar to the 6L6 but pushes out a lower power with less headroom.

KT88

Based on the 6550 with a slight boost, the KT88 has a cleaner sound than even the 6L6, lacking slightly in mid-range richness, the KT88 provides a more responsive low and high end compared to the EL34.

KT66

The predecessor to the 6L6, the KT66 offers a similar response with slight differences, including smoother highs and mids.