5751 Tubes Vs. 12AX7 Tubes – Which Is Better?

Amateur and professional musicians are likely to be in the market for new amp tubes once their old ones start failing. Usually, the question arises when they have to compare a 5751 tube vs. 12ax7 one.

In this article, we’ll explain the difference between a 5751 tube and a 12AX7 one and the sound quality that should be expected from each one. We’ll also highlight the benefits and the downsides that can be sensed in terms of gain and feel when you choose one over the other.

The Gain Factor of the 5751 Tube and 12AX7 Tube

Plugging a preamp tube into the guitar amp is a simple way of changing the gain factor and accordingly, the audio quality. This will refer to how much it can amplify the input signal.

Increasing or decreasing the gain factor will change the way the music feels. Most guitar amp users, especially harmonica users, prefer to reduce the gain to experience different sounds. They also choose to weaken the power of the amp to prevent feedback. However, if you’re looking for sharper tunes, then you need to stick to higher gain.

5751 Tubes

The 5751 tube has a gain of 70%. This is not the perfect gain factor, but this is not necessarily a bad thing.

This tube will provide a somewhat balanced mixture of lows, mids, and highs without washing out the texture. The music still shows all its details without being too dull or muddy, especially with lower tones. Nevertheless, in some cases, you might feel that the audio quality isn’t that impressive.

However, one of the reasons why these tubes are popular is that they’re designed to produce clean audio. They’re less likely to produce microphonic noise, which refers to the metallic noise that vacuum tubes are expected to produce, which ultimately affects the sound quality.

Before opting for the 5751 tube, you need to check whether it’s compatible with your amplifier or not. Although most amplifiers are forgiving and you can experiment with several vacuum tubes, in some cases, the circuit might be designed to work with a specific model of tubes. Choosing a different kind can damage the circuit or might affect the audio quality negatively.



  • They might not work well with your amplifier circuit.
  • Melodies can get too dull.

12AX7 Tubes

These are industry-standard they’re designed to provide a 100% gain factor. This guarantees the crispiest notes and the brightest mixture of lows, mids, and highs.

Unlike the 5751 tubes, no tones will be lost with the 12AX7. The lowest lows and the highest highs will be clear and precise due to the exceptional gain factor that allows for the most flexibility. This is exceptionally desirable when you’re dealing with rock and metal music.  We even have a guide to the best 12ax7 tube for clean tone.

Installing the 12AX7 tube is possible regardless of the circuit you’re dealing with. However, in some cases, it might not be the best thing to do, depending on the manufacturer’s instructions. Moreover, the high gain factor comes with a few drawbacks.

The noise level can be quite problematic, especially with lower notes. The amount of distortion related to the high gain factor is something that most amplifier users have to deal with because it can significantly affect the audio quality.

As a result, most users of the guitar amplifier will always find themselves – as I recently did with my Monoprice tube amp – comparing the gain factor with the noise level obtained after replacing the tubes. Due to the high gain factor, microphonics become more common.

In most cases, you can enjoy excellent audio quality, regardless of the tube you choose. However, it would be best if you experimented with multiple setups until you find the one that works for you.


  • The 12AX7 tube is designed to provide users with a 100% gain factor where no signal is lost.
  • It shows all the details of the audio produced.
  • The lowest and highest signals are adequately amplified.
  • All the details of the music are precise and not washed out.
  • It’s the choice for metal and rock music.
  • It’s almost compatible with all the amplifier circuits.


  • Some noise and distortion can be expected.
  • The crispness of the audio tends to highlight microphonics.

Which Tube to Choose?

Choosing new vacuum tubes for your amplifier is a matter of personal choice, as long as you know that the model is compatible with your circuit. A very high gain factor like the one you get from the 12AX7 tube means that you can sense all the details of the signals. While this might be what you need, it comes with a few drawbacks.

The noise level and the distortion tend to increase when the gain factor is that high. This is why most users will struggle with microphonics, which produces raspy notes that affect the overall audio quality.

To overcome this problem, you can stick to the 5751 tubes. They’re designed to provide a 70% gain factor. That loss of 30% is going to reduce the noise level, distortion, and microphonics that you’re likely to deal with at a higher gain factor. As a result, you’ll enjoy clean and clear sounds without sacrificing the details of the notes as the 5751 tubes produce smooth and calm audios.


It’s not uncommon to be confused while looking for new vacuum tubes for your amplifier. Nevertheless, there are several options that you can choose from depending on your personal preferences and the music you’re usually interested in.

While choosing the 5751 tube vs. 12AX7 one, you need to do a trade-off between the gain factor and the noise level. A lower gain factor might lead to the loss of some notes, but it will reduce microphonics and distortion. The choice is yours, and you can always mix and match tubes to achieve the most appropriate setup.