Do Preamp Tubes Have To Match? What You Must Know

Audiophiles swear by the high-fidelity sound matched preamp tubes give them. But do you have to get matching preamp tubes? What if you can’t find any replacement for what you already have?

Preamp tubes do not have to match to do their job. Because of how they are designed, you do not have to worry about biasing these tubes to ensure that they work perfectly. As such, you can use two different tubes from two different manufacturers as long as they are compatible.

Read on as we talk about preamp tubes and why you can get away with not matching them. We will discuss which preamp tubes are compatible with others and whether or not it is safe to use two different preamp tubes to ensure your amplifier lasts a long time.

Preamp tubes

Is It Safe To Mix Preamp Tubes?

A preamp tube works with power tubes to shape the sound you make on your guitar. It helps to amplify volume while also shaping the tone and character of your sound. If you are doing it right, a preamp tube helps to give you richer distortion and sustained harmonics.

Because of how important preamp tubes are for shaping music, many people wonder if they can use non-matching products in their amplifiers. And would it affect the sound if they put it in different tubes? Most importantly, will their amplifier get wrecked by having mismatched preamp tubes?

It is perfectly okay to mix preamp tubes. In fact, it might be recommended in some cases. The reason why some musicians mix and match preamp tubes is because using different tubes can change or improve the tone of your preamp or amp. 

You can hear slight differences in tone when mixing preamp tubes with varying gain levels. For instance, you can replace a Nomad with a TAD 12ax7 for a cleaner sound. Different brands of tubes also have different characteristics, so changing out a tube with another from a different brand may result in better sound.

Some suggest mixing and matching tubes can bring the most noticeable effects in mid to high overdrive amps.

Tubes Do Not Have To Match

You should remember that preamps tubes and other types of amp tubes need to be replaced over time. That is because these components typically wear out and fade away when you use them. These tubes may also blow out, but it really does not happen too frequently.

Signal tubes like the 12AU7, 6922, or the 12AX7 need to be replaced after about 10,000 hours of use. Similarly sized rectifier tubes such as the 5AR4 last just about the same amount of time.

Power tubes like the KT88 and EL34 are not as long-lasting. These tubes will need to be replaced after about 2,500 hours of use. These tubes can last for weeks or months, while signal tubes can last for years. Usually, after you have been using preamps for a long time, you will be able to tell when the sound is no longer up to par. 

It might be a good idea to replace tubes when they lose dynamics. However, there may come a time when you need to replace a preamp tube that has faded away, but you cannot find a tube to match the one you already have. The good news is that you can get away with an unmatched preamp tube and not encounter any huge problem with your sound.

Non-Matching Tubes Must Be Compatible

So it is safe, and sometimes preferable to have different brands or types of preamp tubes. However, you should make sure that the tubes you are replacing are compatible with the new tubes. That means that you probably should not mix preamp tubes as you would like.

There are several considerations. First, you can swap preamp tubes of the same type. This means that if you have an old 12AU7 tube in your preamp, you can use another 12AU7 tube there.

There are also times when you can use different tubes from the same family or line. For instance, you can substitute the following tubes for a 12AX7:

  • 12AT7
  • 12AY7

The 12AX7 brings with it a gain of 100, while the 12AT7 and the 12AY7 have gain ratings of 60 and 45. Because of the differences in their gain factor, replacing a 12AX7 with either a 12AT7 or a 12AY7 will change the feel and tone of the amp.

To make it easier for you, here are the acceptable substitutes for each preamp tube:

  • 5751 (gain factor: 70): 12AX7, 12AT7, and 12AY7
  • 12AT7 (gain factor: 60): 5751 and 12AY7
  • 12AY7 (gain factor 45): 5751, 12AT7, and 12AV7
  • 12AV7 (gain factor: 41): 12AY7 and 12AU7
  • 12AU7 (gain factor: 19): 12AV7

This Hop Pole Studios YouTube video shows you the subtle differences in using different brands of 12AX7 tubes:

In contrast, power tubes are not that flexible. If you have a power tube, you can use a similar tube from another brand. For instance, you can use Svetlana 6L6 Medium Tubes, Tung-Sol 6L6 STR Power Vacuum Tubes, or Groove Tubes GT-6L6-GE. There will still be subtle differences in the sound, but unlike preamp tubes, these might not even be noticeable.

Why You Can Use Preamp Tubes That Do Not Match

The biggest reason why you do not have to worry about matching preamp tubes is that they are self-biased. That means, unlike changing power tubes, you do not have to worry about matching pairs of preamp tubes.

Self-biased preamp tubes are plug-and-play; you do not need to bias them. The amount of current that passes through these tubes is controlled by a bypass capacitor and bias resistor.

This means they have circuits that are not dependent on the parameters of the tube itself, making it less prone to problems when it comes to the bias point.

Essentially, preamp tubes pretty much take care of themselves when it comes to biasing, which means they will be more forgiving when you use unmatched ones.

Reasons To Use Matched Preamp Tubes

While it is okay to use unmatched preamp tubes, there are some reasons you might like to have them matched up. For one, having matched tubes will ensure you get even gain from each tube.

Another reason you might want to have matched preamp tubes is to make it easier to set up your devices. You do not have to experiment to see how these preamp tubes perform and which combinations will sound best. 

Furthermore, you will likely prefer to have preamp tubes that degrade at the same rate. This way, there will be no need to guess when it is time to replace your tubes. As you use your preamp, the tubes will naturally degrade. If one degrades faster than the other, there might be subtle sound differences, as well. 

Lastly, preamp tubes are often sold in pairs, so it is easy – and may even make more sense – to match them.

Conclusion

Some audiophiles will insist on getting matching preamp tubes to create or listen to music. They argue that it sounds better with even gain. But while they have their opinions, the fact remains that having matching preamp tubes is not at all essential for your amplifiers to work as well as they should, and sometimes, they can even bring subtle changes in tone that you might come to prefer.