Tube amps are regarded by many guitarists as the best of the lot. They have a unique sound that can’t quite be matched by solid state amps.
The source of this sound is the tubes inside the amp. This is also were they get their name from.
But what exactly are these tubes? How do they work and differ from each other?
In this article I will be going over the three common tubes found in amps. I will discuss how they differ in design, and how they compare in terms of tone.
What Are Tubes?
If you have ever looked inside an amp and seen things that sort of look like light bulbs, those are what we call the tubes, or sometimes valves.
These are what essentially power the amp speaker. This then drives the speaker creating sound.
So, why are there different types of tubes? Why don’t we just use the same tubes in every amp?
The reason we use different tubes is because they don’t just power the speaker. Each tube has its own unique sound as well. We use different tubes to get different sounds.
6L6 tubes are high wattage output tubes. These are usually found in amps that are over 50 watts. They can also be found in lower wattage amps, but typically not less than 30 watts.
They are considered the “American” tubes. They are common in Fender amps, which defined the “American amp sound”.
6L6 tubes are known for their bright and clean sound. They have sparkling highs, with deep and clean lows.
Top 3 - 6L6 Tubes
They don’t have too much natural distortion. They are used in high gain amps, though, because of their ability to handle a lot of distortion.
They are typically found in modern metal focused amps. Since these amps use a preamp to create distortion, the 6L6 can focus on driving the speaker. This results in a less scooped tone with a lot of volume.
They can be found in amps like the EVH 5150 and Mesa/Boogie Mark Five. Classic Fender amps like the Twin Reverb and Hot Rod also use 6L6 tubes.
The EL34 can be considered the British cousin of the 6L6. These tubes were used in amps that helped to define big amp stack British rock.
These tubes are known for having a lot of natural distortion. When pushed, these tubes create the classic crunch associated with amps like Marshalls. Their tone is also known for the beefy midrange and a ton of low end.
Top 3 - EL34 Tubes
Just like the 6L6 tube, the EL34 is a high wattage tube. They are found in amps that are 50 watts or more.
EL34 tubes are found in the classic Marshall JCM800. They can also be found in modern amps like the Orange Rockerverb and the Blackstar HT Stage 60.
The EL84 can almost be considered a scaled down EL34. It is a lower output tube, which provides less volume and headroom.
But the EL84 is more than just a weaker EL34. It has a sound that is distinct from the EL34.
In exchange for a lower output, the EL84 has a warmer and sweeter tone. This warmer, sweeter tone is especially present in the low end.
Top 3 - EL84 Tubes
The highs and mids are similar to that of an EL34. The highs are bright and chimey, with a punchy midrange.
Since the EL84 has quite a bluesy tone, it is found in classic blues amps like the Vox AC30 and the Fender Blues Junior IV.
Swapping Out Tubes
You might be thinking, “Can I swap out the tubes in my amp to change its sound?” And the simple answer to that question is no.
There are a few reasons why it isn’t possible to swap out tubes. In the case of the EL34 and EL84, they simply won’t fit.
The two tubes have a different number of pins. This makes it physically impossible for an EL34 tube to fit on the circuit board of an amp that uses EL84 tubes.
The 6L6 and EL34 are a similar situation. Even though they only differ by one pin, you still can’t just swap them out.
This is because the amp’s circuit board is only configured to on tube or the other. There are amps that allow you to use either and swap out the tubes. These usually have a switch or other method of rebiasing the amp to allow using either tube, but these are extremely rare.
The biggest reason why you shouldn’t swap out your tubes is simply safety.
Each of these tubes produce a different amount of power. This means that they allow different amounts of power to go through to the speaker.
As mentioned above, the EL84 is a much lower powered tube than the EL34. And even though they are both high output tubes, the 6L6 has a much higher output than the EL34.
The speaker is configured to handle a certain amount of power. If it receives too little, it won’t be able to produce enough volume.
If the speaker receives too much power, you could damage it or worse. You could blow the speaker, the amp, or even both.
It is just better to replace the tubes in your amp with the exact same models. And even then, it is better to have it done by a professional amp technician.
You should also just replace all the tubes. The odds are that if one has died or blown, the others probably aren’t far behind.
The tubes aren’t the only things that have power running through them. There are a number of other parts in the amp that have power running through them, and they can retain a charge long after the amp is turned off.
If you accidentally touch one of these parts, you can easily get shocked, and it could be fatal.
Making Your Tubes Last Longer
At some point you will need to replace your tubes. This will typically need to be every 2 or 3 years, depending on how often you use the amp.
There are a few things you can do to make the tubes last longer.
Warm the Tubes Up
The easiest is to turn your amp on and let the tubes warm up for a few minutes before playing. The tubes will then be warm enough so that the signal being sent through them won’t cause them to become hot too quickly.
If you have ever seen a cold glass being exposed to high heat really quickly, you know what happens, the glass will explode. Since tubes are made from glass, the same thing applies here.
It won’t happen if you play immediately after turning the amp on, but the risk is there. You will weaken the glass if you do this every time, and the tubes will blow eventually. Allowing the tubes to warm up will also make them sound their best.
Store the Amp Properly
When you aren’t using the amp, you should store it in a cool, dry place. Humidity and rapid temperature changes will also weaken the tubes.
This is especially important if you live in a humid or cold climate. A closet or cupboard should work as a good place to store your amp. And if you are concerned about humidity, you can try putting a humidity control pack on or inside you amp.
Keep the Tubes Clean
If the tubes of your amp are exposed, make sure to keep the tubes clean. You can use pressurized air to clean out dust, and use a dry cloth to wipe the tubes clean if you can reach them.
Dirt isn’t going to damage your tubes, but it can affect their tone.
Match the Impedance
If you are using your amp with a cabinet, make sure their impedances match. If their impedances don’t match, you could have sound issues and potentially even damage the amp or cabinet.
Also, make sure you are using the correct voltage from the mains. The correct voltage is indicated at the back of the amp and can usually also be adjusted.
Which Tube is Better?
There is no real answer to which tube is better. Each tube has its own distinct tone.
The one you prefer is going to depend entirely on which sounds better to you. Each one is also better suited to certain styles and genres.
If you play metal, for example, you want an amp that uses 6L6 tubes. Their higher output gives them more headroom, allowing them to handle more gain.
For blues, jazz, country, etc., an amp with EL84 tubes is going to be better. Their warmer and sweeter tone makes them great for a cleaner tone.
I hope this article has given you a better understanding of tubes. Hopefully you now know the differences in tone and design.
There are other tubes as well. These three are just the most commonly used in amps.