One of the best ways to customize your amp’s sound is by switching out the tubes. This can really make a difference to the overall output and capabilities of your guitar rig. The 12AX7 is a high gain small signal pre-amp tube which can produce brilliant guitar tones.
Most amplifiers now use 12AX7 dual triode tubes in the pre-amp. This is because they produce a reliable, low-noise and high-gain output and have been optimized for modern tube amps.
5 Best 12AX7 Tubes for Bass & Guitar Amps
The Genalex Gold Lion 12 AX7 tubes are clear and powerful. These pre-amp tubes are a great way to upgrade your amp, adding warmth and a light crunch to the tone. They are made with premium gold pins and are easy to install into your amplifier.
A great feature of these amp tubes is their ability to suppress feedback. As the 12AX7s are known to sound “hot” and encourage some distortion, feedback can be a common issue for a guitarist. Genalex make resistance to feedback a priority so we don’t have to worry about it on stage.
Overall, these tubes provide an affordable and reliable option for upgrading your amplifier.
Mesa/Boogie is known as the first manufacturer of boutique amplifiers. The quality of their amp components has ensured their longevity since the late 1960s. Keith Richards and Carlos Santana are known to have used their amplifier related services and products.
The 12AX7 tubes are premium quality pre-amp tubes which give a guitarist the maximum amount of high-gain output with exceptional consistency. The tone is reliable and warm, lending itself perfectly to that on-the-edge of clean sound which tube amps provide.
These tubes also have a smooth, balanced response which is spread evenly over the tonal spectrum. If you use effects pedals, these tubes provide the perfect blank canvas for you to create your sound.
The Mullard 12AX7 tube is a reliable replacement for your pre-amp tubes. They will easily slot into most vacuum tube amps and provide a solid tonal foundation for your sound to be built upon.
This item is sold singularly, and is versatile enough to work with one of your old 12AX7 tubes. This makes it perfect for a replacement if one of your pre-amp tubes has started to lose power.
Made in Russia, this tube has a robust design and is very straightforward to install. If you want a no-nonsense, easy replacement process then this is probably the right choice for you.
The Tung-Sol 12AX7 is a premium twin triode which produces high gain. It’s an improved reissue of the Vintage NOS Tung Sol model, with added low-microphonic noise output control.
This tube produces slightly more bite than a typical 12AX7 does. This results in added tonal warmth and linearity, making for clear transitions between the many frequencies of an electric guitar.
If you play lo-fi, garage rock or other “rough and ready” genres of music, this pre-amp tube is ideal. It’s sold as a single tube so if you need a full replacement, you will need to order two, but it’s also compatible with existing 12AX7s if you just require one replacement.
Electro-Harmonix is responsible for some of the best-known effects pedals ever made. Their attention to detail when it comes to tone and sound is industry-leading. This pair of 12AX7 tubes sound as good as you would expect them to, coming from such a well-known manufacturer.
The pre-amp tubes are matched for gain and power, and the built in spiraled filament reduces the unwanted noise associated with pre-amp tubes. This valve has a rigid internal construction and thick glass casing. It breaks up easily and is well suited to both modern and vintage high-gain guitar amps.
There is a detail which these tubes provide, probably down the low microphonic output. This feature really allows you to hear the tonal qualities of the amp without the annoyance of unwanted hum or buzz.
The Most Common Tubes on the Planet
Most tube based guitar and bass amplifiers utilize the 12AX7 pre-amp tubes in their design. Many amps use multiple 12AX7s. They are without a doubt the first choice for tube amplifiers due to their low noise characteristics and the high gain output they provide.
These tubes were originally developed as a replacement for the 6SL7 which produced problematic microphonic noise and were bulkier in design.
Basically, if you can think of an amplifier brand, it’s likely that they use 12AX7 as their preferred pre-amp tube. Since the early 1950’s, these tubes have been a staple of guitar amplification, yet they don’t really seem to get the credit they deserve in my opinion.
Even with all of the modern developments in audio technology, the 12AX7s are still used in most amps as they provide the sound which we as guitarists have become so familiar with.
The fact that over two million 12AX7s are produced annually proves that they are still a hugely important component of guitar and bass amplification.
A Brief Overview of Microphonics
When you are looking for the best 12AX7 tubes, a term which may keep appearing is microphonics. This refers to issues which arise with an amplifier. When a tube goes microphonic, it has become susceptible to unwanted external noise, which it amplifies. This commonly causes the tube to ring if it’s tapped.
A working tube with low microphonics will usually make a thud sound when used in the input position. A tube which is microphonic, however, will produce a high-pitched noise which sounds like ringing. If you are testing your tube by tapping it, be careful to be gentle as tubes can be damaged from excessive force.
Microphonic tubes are not always a bad thing. In fact, all tubes are microphonic to an extent, and it’s impossible to completely eliminate this. If your tube does become overly microphonic, you can still use it in a position where the signal of a guitar or bass has already been amplified, but not in the input or pre-amp position.
I would personally get rid of a tube if it has become so microphonic that it’s unstable. If it produces a slight ring and still has stability, there’s no reason the dispose of it just yet.
12AX7-A vs. 12AX7-B
There are actually two types of 12AX7 tubes, almost identical in composition but with slightly varying qualities and capabilities.
The main difference is that the 12AX7-A produces more gain and noise. This makes them better suited for overdriven or distorted sounds. Manufacturers like Mesa/Boogie and Peavey use the 12AX7-A models for the high-gain sound they produce.
12AX7-B tubes also produce plenty of gain, but without the excess noise. This makes them better suited for cleaner playing and styles in which guitar noise may interfere with the vocals or other instruments.
Basically, if you are the kind of a guitarist who loves lots of gain and isn’t worried about other noise creeping in, the 12AX7-A is perfect. If you would rather have more control over the tones with less bite, then the 12AX7-B is for you.
Gain and Volume
One of the common mistakes guitarists or bassists make when choosing tubes and other components for their amplifiers is assuming that louder is better.
This is not always the case though. The days of amps having to power a room are gone, thanks to digital interfaces and microphones which allow smaller, less powerful amps to be further amplified in order to fill larger spaces.
Gain is a term which guitarists like to discuss, and it’s certainly an important aspect of the overall sound. It can be tempting to drive the gain up as high as it can go before it starts to cause feedback issues, but I like to think of gain as something which gives a gentle boost of aggression to the sound.
In many cases, less is more when it comes to the gain and volume of an amp. 12AX7s and other similar tubes will sound best when they are used within their capabilities. Pushing them can create interesting sounds, it’s important to find a middle ground so that you get the best out of your rig.