12ax7 vs 12ax7a: Analyzing the Differences Between Amp Tubes!

There are lots of 12AX7 tubes available right now. Each 12AX7 has a minor yet audible difference in tonality. 

Take 12AX7 and 12AX7A for example. These two have very distinctive characteristics to look at.

So, what is the difference between 12AX7 vs 12AX7A?

12AX7 only has a parallel circuit whereas the 12AX7A model can use a series or parallel circuit structure. It also had a controllable heater warm-up that could be used in a series of filament circuits. However, except for this, the gain and other qualities remain almost similar.

So why all the different names, and are they still relevant today? Let’s find out!

12AX7 vs 12AX7A: A Quick Difference

Comparing 12AX7 against 12AX7A is just as confusing as comparing El84 and vs 6v6, or the 5881 and 6L6. You will find out why it is difficult shortly.

First, let’s see a quick difference between 12AX7 VS 12AX7A tubes. This will help you to understand the similarity and dissimilarities between both tubes.

Differences12AX7 12AX7A
AmpsFender, Laney, HiWatt, Marshall, Boogie or Soldanol Fender, Marshall, Vox’s, Supro’s
Voltage RateLower Higher plate Voltage rate
AvailabilityLess AvailableAvailable
CompatibilityParallel filament circuitsParallel & series filament heater circuits
Durability1-5 years4-6 years
Gain100 mu100 mu
Heater CircuitsParallelBoth Parallel & Series
Microphonic NoiseMore NoiseReduced Noise

The table shows that, except for heater circuits, these two tubes don’t really differ from one another.

12AX7 vs 12AX7A: A Brief Discussion

A 12ax7 tube and a 12AX7A tube are nearly identical in today’s manufacturing. Sovtek has the 12AX7WA, 12AX7WB, and 12AX7WC, for instance.

Source: en.wikipedia.org

These tubes are almost exact replicas with a few minor differences. On the same 12AX7 tube, Shuguang has also applied labels for 12AX7, 12AX7A, and 12AX7B.

The “S” suffix can be found on several tubes, such as the ECC83S and 12AX7LPS. In these situations, the letter “S” denotes a spiraling heater filament in the tube. 

However, all current 12AX7 tubes are made with spiral heaters. Therefore, having an “S” suffix no longer means anything exceptional.

In modern manufacturing tubes, suffixes like 12AX7A, 12AX7B, etc. might be regarded as part of product names. Try not to stress too excessively over it.

However, it’s better to know how ‘A’ was used to differentiate between the two previously. 

So, let’s jump into the main discussion.


The difference between series and parallel is evident when applied to circuits. One works better than the other. Although most circuits these days are parallel. 12AX7 initially supported only parallel filament circuits when it was introduced to the market.

difference between series and parallel
Source: nostubestore.com

However, 12AX7 was in desperate need of an upgrade when series circuits also entered the market. Additionally, a series filament was less expensive.

So, what is the difference between 12AX7 and 12AX7A?

Compared to 12AX7’s single series construction, 12AX7A was constructed to operate in either parallel or series filament circuits. In this variation, a regulated heater warmed up in preparation for usage in a series filament circuit. 

Cheap tube radios use it as a cost-cutting measure.

Winner: By having both series and parallel filaments 12AX7A is the clear winner between the two.


The lifespan of a 12AX7 tube is often very prolonged. So, how long do 12ax7 tubes last?

Depending on use, 12ax7 tubes can last 1 to 5 years or more. Heat and usage are the main causes of tube wear. The cathode, which emits electrons, will wear down over time.

A decent guideline for replacing is every 5000 to 10000 hours. In a gain stage, a 12AX7 may operate for a longer time because it produces little heat. In spite of being more reliable, a parallel circuit uses more energy than a series circuit.

12ax7 tubes
Source: talkbass.com

The mix of parallel and series circuits gives 12AX7A a longer tube life. This can be considered a significant advantage. Sylvania Electric developed a better 12AX7A structure with a helically wrapped heater.

Winner: For the benefit of both circuits, 12AX7A is still the better choice. Even though it has a shorter service time.


Performance with high gain and low gain has always been a topic of discussion. The dual triode tube 12AX7 has a high gain. In the matter of gain, different 12AX7s frequently differ by a few points. This doesn’t imply that one will be higher than the other.

Speaking of gain, you might be thinking how many pins does a 12ax7 have?

Both 12ax7 and 12ax7a have a total of 8 pins. So, there are no significant differences there.

The 12AX7A preamp tube also gives the most gain and overall tone quality. You get a constantly broad and expressive tone spectrum with controlled, clean frequency response.

12AX7A preamp tube
Source: thegearpage.net

Compared to the competition, the Bugera 12AX7A is the best preamp tube for all key gain stages. Without a doubt, it ranks among the greatest 12AX7 tubes ever made.

Noise floor and tone are influenced by gain. These tubes each have a gain of 100 mu. The tone isn’t always better when the gain is higher. Therefore, we advise you to experiment with various 12AX7 tubes to see what suits you best.

Winner: This part has no winner because both of these tubes have the same amount of gain. 

Heater Circuits

The alphanumeric name “12AX7” inscribed on the side is more than just a model number. It offers a lot of details on the tube.

The ’12’ denotes the heater (the component that illuminates orange whenever the tube is turned on). It states that the tube needs 12 volts to function.

The letter “A” denotes the tube’s function as an amplifier. The ‘X’ stands for the electrical properties of the tube. Such as the gain factor, resistance, etc. And the ‘7’ stands for the number of active pins.

Initially, parallel filament circuits were the only applications for the 12AX7. The 12AX7A was designed to work in circuits that employed either parallel or series filament heaters.

Nowadays, you’ll almost never come across a series filaments circuit and only parallels are used. 

Winner: Although this distinction is meaningful now, for having both circuits 12AX7A is the better choice.

Microphonic Noise

Tubes are capable of detecting vibrations and producing them as signals. Microphony is the term used to describe this phenomenon. 

All vacuum tubes have some degree of microphony. The impact is more noticeable with such a high gain tube like a 12AX7.

It’s advisable to choose tubes with lower microphone sensitivity if your amplifier has a very high gain. This is to lessen the possibility of encountering issues

By using a shorter plate structure, the new 12AX7A design explicitly addressed microphony issues. This shorter plate also features a spiral filament pattern. The microphonic noise was improved in this manner.

Winner: 12AX7A is the clear winner here.


These two tubes provide a musical tone that is smooth and clear. Each has a certain amount of microphonic noise, but it improves the sound across the full spectrum.

There have been no observable spikes or weak points in the mid, high, or low end. The middle response is well-balanced. The bottom end is warm and rich, and the highs are extremely smooth.

But the 12AX7A tube has much more extremely low audio and microphonic noise levels. Because of the shorter plate design. So in comparison to the 12ax7, the tone quality is substantially better.

Winner: 12AX7A takes first place in this battle.

Time for Decision

When it comes to picking between the two it varies depending on the maker. The components utilized, quality, and, most importantly, how these old tubes were kept is also deciding factor.

Both of these tubes are capable of producing extremely smooth audio with powerful bass. It is not excessively sweet and also has warm mids and highs. So, I strongly urge you to explore these recommended preamp tubes to get a better idea-

JJ Electronics Amplifier Tube (T-12AX7-S-JJ) is definitely one of the best. This manufacturer has been in the preamp tube industry for a long time.

Another great choice will be ArkiFACE Pair of JJ ECC83s/12AX7. These tubes will also serve you for an extended period of time.

Electro-Harmonix Matched 12AX7 Pair can heavily reduce the preamp noise. So, you can’t go wrong with these preamp tubes.

Despite the fact that series are seldom ever utilized today, 12AX7A continues to be the finest option.

As a more affordable option with an upgrade to the previous version, definitely go for 12AX7A.

Frequently Asked Questions (FAQs)

Is It Possible to Use the 12AX7 and 12AU7 Interchangeably?

Yes, it is possible. However, to prevent harming your amp, carefully verify the circuit diagram and documentation before replacing a piece. Your amp shouldn’t technically be damaged for swapping a 12AX7 for a 12AU7 tube in it.

Which 12AX7 Has the Better Tone for Metal?

The top metal-compatible 12AX7 tube in current manufacture is JJ ECC83S. This tube can be useful if you prefer a darker rhythm sound. They are forceful and warm. JJ ECC803S is a more well-balanced version of the ECC803S.

Do 12AX7 Tubes Have to Match One Another?

Matching these preamp tubes, for instance, 12AX7s is a good idea but not necessary. But it will guarantee that you obtain an equitable gain from both tubes when they are matched. These tubes including the 6DJ8 type are referred to as linestage tubes.

End Words

Our discussion of 12AX7 vs 12AX7A is now complete. There is little to no distinction between the two, thus either one is a great pick. But we advise you to choose 12ax7a over the alternative for the aforementioned quality.

The tube’s suitability for you should also be verified using your own equipment. As each device could have different suitability.

Until next time!

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