How do tube amps work?

Many people ask themselves “how do tube amps work” in relation to a transistor (or Solid-State amp if you like) amp
It can be hard to understand how they work, but I will try to keep it simple.

To start with it, you have to understand that a tiny signal is created by your guitar’s metal strings to oscillate the pickups. Guitar pickups are a magnet wrapped with a coil of wire. Read more about Single coil- v.s. humbucker pickups.
Driving the amp speaker is basically the opposite of how the signal started: The speaker exists of a coil of wire moving within a magnet, which drives a speaker cone that moves air.
It may be interesting to learn about the difference between open- and closed back cabinets.

What is the role of the tubes

The role tubes play is turning the quiet, tiny guitar signals into big sound.
There are various types of vacuum tubes, but in the guitar amp world, three types are most common:

1. Preamp tubes
2. Rectifier tubes
3. Power amp tubes

Tubes shown above are typically used as preamp tubes. Please note that ECC83(S) is the European equivalent of the 12AX7.

How preamp tubes work:

When learning about how do tube amps work, you have to start with the preamp stages. Its job is to take the signal from the guitar and amplify it to a level that can drive the output section.
This is done in stages because the guitar signal is very weak.
The first tube (called V1) will take the guitar signal and amplify it by about 100 times before we do anything with it in the amp. This process repeats in the other preamp (V2, V3… etc.) tube positions as well.

How does a tube make a signal 100 times bigger?

The V1 tube has about 300V DC on its plate.  
The small guitar signal creates electrical movement on the screen of the tube, which causes movement on the plate. This gets significantly amplified due to its high-voltage potential.

Because these are still small signals, the tubes are small. A 12AX7-type tube has two sections. In this case, V1 can also be used as a second gain stage or the first stage for another channel input of the amp. Let’s call it multifunctional.

What does a rectifier tube do?

Rectifier tubes helps converting the AC from the wall into DC.

A rectifier is not some sort of transformer, but rather a device that converts alternating current (AC) to direct current (DC) using semiconductor devices like diodes or thyristors.
The amp’s power transformer only runs on AC, so it’s up to the rectifier tube to create DC, which is needed by the other tubes.
The tubes that we use in this part of our amp are specialty tubes, designed to do this one particular task and they’re are not interchangeable with preamp and power amp tubes.

Rectifier tubes usually do not affect the tone in your tube guitar amp.
Most commonly you will find a 5AR4/GZ34, 5U4, 5Y3 or EZ81 as tube rectifiers in guitar amps.

What do Power Tubes do?

Power tubes exist of a single stage inside.
They do more work than the preamp- and rectifier tubes. In fact, they’re the engine of the amplifier.

The power tubes drive the output transformer, which pushes the speaker cone to move air.
The overall function is the same as for the preamp tubes, but at a higher level.
Power tubes globally run at usually 400–500V DC; More voltage means more pedal to the metal.

The power tubes need a high-voltage DC to operate, but a speaker only needs 10–30V AC work properly.
The output transformer separates the AC guitar signal from the DC power supply.

So, in simple words we now know more about how do tube amps work.

What is the difference between all different power tubes in tone.

We all know the EL34, EL84, 6V6, and 6L6 tubes.
Each has its tonal characteristics and power output, of course in combination with the preamp tubes.

Key differences between EL34 / EL84 / 6V6 / 6L6:

• EL34 is a power pentode, meaning it’s designed to handle a significant amount of power and has five electrodes:
  (cathode, control grid, screen grid, suppressor grid, and plate)
• EL84 is a “medium” power tube and contains five internal elements: (cathode, control grid, screen grid, suppressor grid, and plate)
• 6V6 is a beam power tetrode. This is a type of vacuum tube containing four electrodes: (cathode, control grid, screen grid and anode)
• 6L6 is a tetrode, but with special “beam-forming plates”. The tone is more scooped than an EL34.

Typical power tubes. From left to right: EL84 / EL34 / 6L6

What is scooped tone?

A scooped tone is typically a sound where the mid-range frequencies are reduced.
The tone looks equalization wise “V-shaped”.
It is big, bold and heavy, with crisp highs and a thundering bottom-end.

What are the elements of power tubes?

• Cathode: Emits electrons when heated.
• Control Grid: The primary grid that controls the flow of electrons from the cathode to the anode.
• Screen Grid: Positioned between the control grid and the anode, it’s held at a positive voltage and acts as an electrostatic shield.
• Suppressor Grid: Kills secondary emission*. This effect can adversely affect the output of the tube. In order to get rid of this effect, another grid, the suppressor grid, is inserted between the screen grid and the plate.
• Anode (Plate): Collects the electrons and forms the output of the tube. 

The difference between Pentodes and Tetrodes is as follows:

Pentodes have five elements: cathode, control grid, screen grid, suppressor grid, and plate. 
Tetrodes have four elements: cathode, control grid, screen grid, and plate. 

In general, EL34 and 6L6 tubes are typically used in higher wattage amps. Usually amps that are over 50 watts. 
EL84 tubes are used for lower wattage amps from 20 – to 30 Watts.
But EL84 have essentially the same sonic flavor/characteristics as EL34 tubes.

What means secondary emission*:

Secondary emission is when electrons pulled from the cathode, knocking other electrons off the plate.

Digging deeper on the specifications on all of this will go too far in my opinion.
So, if you want to know more specific details on Pentodes and Tetrodes, please check the internet.  

Do power tubes have to be paired

Yes, power tubes have to be paired (or matched) for optimal longlife- and balanced performance.

Matched tubes ensure that each tube in a pair (or quad) contributes equally to the amplifier’s output.
This leads to a more balanced and even sound.

When tubes are matched, they share the workload, preventing one from being overstressed.
You might be interested in our blog about the difference between a Solid-State- and Tube amps. In this blog you will read more specific information about tube amps as well.

Unmatched tubes can cause unevenness in the output, potentially leading to distortion and a less clear soundstage, especially in the bass frequencies. 

Proper Bias:

Many amplifiers require a specific bias setting for optimal performance. Matched tubes help ensure that the bias setting is correct for both tubes, leading to better performance and potentially longer tube life.

How to bring the best amps sound to the audience?

Of course, having a great amp (and tube amps may be preferred) is important besides a good guitar & effects pedals.
But placing the right microphone and placing it correctly in front of your speaker will help to let you sound like a pro.

Tube name	Power output (pair)	Plate voltage	Found in amps like
EL34	< 30 – 50 Watt	400 – 800 V	Marshall, Hiwatt
EL84	< 15 – 20 Watt	300 – 400 V	Vox AC30 – AC15, Dr.Z Stang Ray, Dr.Z Z-Wreck
6V6	< 12 – 20 Watt	300 – 400 V	Fender DR amp, Princeton
6L6	< 30 – 50 Watt	400 – 500 V	Fender Twin Reverb, Bassman, Peavey 5150, Soldano SLO-100

Tonal characteristics

Tube	Tonal Qualities
EL34	Aggressive mids, crunchy and punchy, tight low end, classic British rock/Marshall tone
EL84	Bright, chimey, glassy highs, sweet compression, midrange sparkle — classic Vox “British Invasion” sound
6V6	Warm, smooth overdrive, round highs, creamy breakup — vintage American low-watt tone
6L6	Clean headroom, big low end, scooped mids, punchy and clear — classic American high-headroom sound (Fender)

6V6-S power tubes in a Fender Deluxe Reverb Amp, with on the far left a rectifier tube (5AR4 from Sovtek).

Usage in Music Styles;

Tube	Best For
EL34	Hardrock, classic rock, metal
EL84	Indie, classic rock, blues, country (i.e. Brad Paisley)
6V6	Blues, jazz, classic rock, country (i.e. Brent Mason)
6L6	Clean genres (jazz, country), but also great for rock and blues when pushed

In short about preamp tubes

The 12AX7 and 12AT7 are usually used as preamp tubes.
Of course there some more like the EF86 etc.
Both are dual triode vacuum tubes, but they have different electrical characteristics.
This will affect how they behave in your amp.

12AX7	100 (high gain)
12AT7	60 (moderate gain)

Shown above the preamp section of a Fender Deluxe Reverb amp. And in perspective of how do tube amps work, we will let you know what role these 3 different preamp tubes play in the amp.

V1 (12AX7) is the one far right. Drives the first and second gain stage of the standard channel.

V2 (middle and 12 AX7 as well). Drives the first and second gain stage of the vibrato channel.

V3 (12AT7) is the reverb driver tube. This tube is only in use in the vibrato channel

Impact in amps: The 12AX7 will produce more distortion and signal amplification than a 12AT7.
The 12AX7 is often used in preamp stages to drive tone and saturation.

12AX7 tubes: More gain = more overdrive, crunch, sustain, and compression. Classic preamp tone for rock/blues

12AT7: Cleaner, tighter sound with less distortion and slightly faster response. May sound more articulate but less “aggressive”.

Do preamp tubes also need to be paired?

No, preamp tubes generally do not need to be matched, unlike power tubes. 
Preamp tubes are wired in series, meaning they work independently and don’t interact with each other in a way that requires them to be matched for balanced operation.

Final thoughts on how do power tubes in tube amps work

EL34 vs 6L6: Both powerful, but EL34 has more aggressive mids (British), while 6L6 sounds cleaner and has a more scooped (American) tone.

EL84 vs 6V6: Both lower power; EL84 has more shimmer and compression, 6V6 is smoother and warmer.

Although the power tubes are the “engines” of your amp, the role of the preamp tubes absolutely is important as well.
They have a role in how much clean headroom your amp has, as they drive the power tubes.
Read more about what headroom means in guitar amps.

Guitar essentials:

In guitar essentials we write about interesting things every guitarist should know a bit of, especially when you’re new to (electric) guitar. In this blog we talk about “how do tube amps work”.
We definitely don’t dig deep into theories or technical aspects.
You will find many scientific documents about anything somewhere on the internet.

About ChickenPicks guitar picks

Actually we are a company that invents different types of guitar picks. For me it always has been interesting to understand more about (better) tone. This, including the need of finding picks that are more comfortable to play with, I started to learn about everything what may be helpful.

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