Do Preamp Tubes Need to Be Matched?

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Perhaps you are looking to replace worn-out preamp tubes, or maybe you are looking to upgrade to more robust tubes. But the no. 1 question many people replacing their preamp tubes for the first time ask is, do preamp tubes need to be matched? Well, after hours of research, here is what I found.

In short, no. Preamp tubes don’t need to be matched. The two triodes in preamp tubes operate independently in different circuits. So there is no need to match them.

The Idea of Preamp Tubes Matching

I think before we dive into whether or not preamp tubes need to be matched, we need to understand why preamp tube matching is even considered in the first place. So let’s talk about it briefly.

Nowadays, the commonly used preamp tubes in guitar amps and high-fidelity audio equipment are dual triode preamp tubes. Dual triode simply means there are two triodes in each tube. This essentially means, for every preamp tube, there are two “amplifiers” in every enclosure. The 12AX7, 12AT7, 12AU7, and 6922 are all preamp tubes with a dual-triode configuration.

The basic idea behind matching preamp tubes is that all the two triodes in the tube will have the same electrical or electronic properties.  

And why is that beneficial? Well, according to matched preamp tube sellers, if the two triodes have the same electronic properties, they can be interchanged, and there will not be any noticeable difference. 

Also, having matched preamp tubes means they are likely to have the same preamplifier gain and consistent performance. That’s pretty much the benefits you get from matching preamp tubes, according to matching preamp tube manufacturers’ claims.

However, that’s far from the truth. There is no inherent benefit to matching preamp tubes. And you’ll understand why in the next section.

Why Preamp Tubes Don’t Need to be Matched

The main reason why preamp tubes don’t need matching is that the two triodes in a preamp tube are independent. What do I mean? The two triodes are not in the same electrical circuit. Both triodes have their own electrical circuit. This means, whether the triodes match or not, it won’t affect the sound it produces in any way.

What About Phase Inverters?

Found in every amp is a phase inverter (or phase splitter). For those who don’t know it is, let me briefly explain what it does.

A phase inverter receives an audio signal from the preamp, duplicates the signal, and sends the signal to the power amp’s left and right channels.

After duplicating the signal, the phase inverter will invert (or flip) one of the signals so that it is a mirror of the original signal that was sent by the preamp. And then, it will forward the signal to the power amp tubes.

Phase inverter tubes are similar to regular preamp tubes. Also, they are usually the closest preamp tubes to the power tubes. But do phase inverter tubes have to be matched?

Ideally, phase inverter (or phase splitter) tubes should be matched. This will ensure that it sends identical audio signals to the amplifier’s power tubes.

Phase inverters may work fine when they are not matched or balanced in an amp. In fact, the sound produced by an unmatched phase inverter can be quite desirable. Some musicians and manufacturers choose to use unmatched phase inverters to get a rich harmonic tone, which wouldn’t have been achieved with a matched phase inverter.

However, it’s a good idea to use a matched phase inverter, especially if your amp is a push-pull amplifier.

Things to Consider When Buying a Preamp Tube

If you plan to replace a preamp tube in your amp, here are some essential things to look out for to get the best option.

Type of Tube

There are many different types of preamp tubes available today. And every amp manufacturer decides which type of tube to use to get the best performance out of their amps.

Some of the most common preamp tube types available today are the 12AX7, 12AT7, 12AU7, 12AV7, 12AY7, 6CG7, and 5751 tubes. Obviously, there are more options available, but these are the more common ones.

Before you go out shopping for a new preamp tube, here is what you need to do. Check the tube enclosure of the preamp tube you want to replace. The type of tube will be written clearly on it. This is usually an alphanumeric key with four characters. Take note of it.

Ensure that the replacement preamp tube you are buying is the same type as the old one. Check that the two alphanumeric keys on both tubes match.

For instance, if the preamp tube you are replacing is a 12AX7 tube, make sure you find a replacement preamp tube, which is also a 12AX7, and so on.

Matched or Unmatched

There will be a matched and unmatched version for every type of preamp tube in most tube amp shops. You need to decide which option to go for. Matched preamp tubes are a bit more pricey than unmatched versions. So that’s something to take note of.

As we have already discussed, you can definitely go for preamps tubes with unmatched sections, and you’ll have no issues whatsoever. 

However, if you are replacing the phase inverter tube, I recommend you go for a matched tube.

Do Different Preamp Tube Brands Make a Difference?

If you are out shopping for a newer preamp tube, should you care about which brand it is? Does it make any difference which preamp tube brand to go for?

Short answer, yes. Preamp tubes made by different manufacturers sound different. Also, some brands of preamp tubes last longer before they wear out.

Every preamp tube manufacturer uses different electronic components to build their tubes. These electronic components will usually have different electronic properties, which will directly affect the amp’s output sound.

Also, some preamp tubes have a much better build quality. This means they will last longer than usual. 

I’d recommend you purchase a few preamp tubes from different brands and test all of them. Place each tube in the V1 position, one at a time, and play your guitar through them to see which ones give you a sound that you enjoy the most, and stick to that.

After some research, I found out Tung-Sol tubes have a very good reputation as one of the best-sounding preamp tubes available today. They are also well built, so they are going to last for a while before they eventually wear out.

Another type of tubes you can look into is NOS tubes. NOS simply stands for New Old Stock, and it’s used to refer to tubes that are not made by their manufacturers anymore but haven’t been used before.

NOS tubes are rare because they are not in production anymore, so you’ll have to spend some extra cash to get them. It has a lot of hype when it comes to tube preamps and amps, so I think it’s worth checking out as well.

Conclusion

In summary, it’s not required to get a preamp tube with matched sections. Many preamp tubes in amps have unmatched sections, and they work very well without any issues. So you’ll definitely do just fine with unmatched preamp tubes.

However, you should consider getting a matched tube for phase inverters in an amp.