There are many amplifier tubes out there, including the popular 12AX7 and the 7025. So what are they? And how do they compare to each other?
If you’re looking for answers to these questions, you’re in the right place. Today, I’ll put the 7025 tube vs. the 12AX7 counterpart, so you can have a better idea about both of them!
What Are Amplifier Tubes?
When you’re playing the guitar, the amplifier’s tubes are responsible for producing the sound you hear. They achieve that by elevating the little signals coming off the pickups from your guitar.
After that, they take these tiny signals and amplify them into something large enough to move air. This power is able to drive speakers to produce sound waves.
All amplifiers have similar components. When you look at the back of any amplifier, you’ll find a set of glass tubes that look like light bulbs with a pointed protrusion on the top.
Each one of these tubes serves a different purpose. The tubes we’re comparing here belong to the preamp tubes, so let’s explain that.
The goal of the preamp tubes is to condition the properties of the incoming signals from the guitar. It does that by elevating the incoming signals up to a nominal level. Once the signals are large enough, the other tubes can work on them.
Over the years, guitarists discovered that when you push these tubes hard, the signals start to distort. Most tube amplifiers in the market use at least one 12ax7 preamp tube. However, this number can jump up to 5 tubes in some complex set-ups.
This is also known as the “cascading gain stages”. It happens when you can achieve the effect of more than one preamp tube within the same amplifier. This can make a more pleasant and richer distortion
12AX7 Preamp Tube
Design and Construction
12AX7 preamp tubes have 9 small pins that are arranged in the form of a small circle with a diameter of 0.5 inches.
These pins have unequal gaps between them to make sure that you can only plug the tube in one way. If you look at the pins, you’ll notice that there’s a large gap between pin 9 and pin 1.
The 12AX7 also has a dual-triode construction. This means that it carries two identical triodes within the same envelope.
Each one of these triodes consists of three electrodes, hence the name. This means that you can get two gain stages with a single 12AX7 preamp tube. This means that it saves you the price of 2 separate preamp tubes!
12AX7 preamp tubes have a high voltage gain with a high amplification factor. This is defined by μ or mu (pronounced as Miu). That’s why it heats up pretty quickly when compared to other preamp tubes.
This factor refers to the level of amplification this preamp tube can achieve compared to other preamp tubes. This includes other tubes, such as 7025, 12AT7, 12AU7, and others.
The 12AX7 has a great level of amplification compared to other models. However, it does have a slightly louder level of noise when compared to 7025. Still, your ears might not be able to distinguish the difference.
A single 12AX7 preamp tube is the cornerstone of guitar music application and the simplest configuration.
7025 Preamp Tube
The 7025 preamp tube is also developed and made by the RCA Engineers Company. It was also released to the public as the “7025 preamp tube” in 1946.
The 7025 preamp tube was designed for military use before RCA decided to release it to the public.
Design and Construction
The 7025 valve has a 9-pin construction design. The 9 pins are arranged in a way where there’s a wider gap between the 1st and the 9th pin. This is pretty identical to the arrangement of the nine pins in the 12AX7 preamp tube.
The two triodes are also packed within the same tiny glass envelope. This means that you can also get two gain stages with a single 7025 preamp tube.
This is another major similarity between the 7025 preamp tube and the 12AX7 preamp tube. Each triode has 3 electrodes. These ones are the cathode, the grid, and the anode.
It has two identical triodes that produce high voltage gain. In fact, it can produce about 100 times more gain in theory. However, in real life, you can achieve about 60 times more gain only.
Similar to the 12AX7 preamp tube, the 7025 features a compact build that doesn’t affect the sound output. This makes it the preamp tube of choice by many guitarists.
That’s why the 7025 preamp tube is one of the few preamp tubes that have been in continuous production for over 70 years.
What’s the Difference between Them?
Based on what you’ve noticed, both preamp tubes are pretty similar in construction. Additionally, they carry a much similar performance. So what’s the difference between the two valves?
One of the very few differences between the preamp tubes is that the 7025 produces a much higher voltage gain. However, this is only in theory.
Another theoretical difference between the two is that you can get a bit lower level of noise and a quieter hum with 7025.
The 7025 tubes are also a bit more expensive than the 12AX7s. On average, you can find 12AX7 tubes at less than $20. On the other hand, the 7025 tubes can reach up to $35.
Both of them are a great investment because the dual-triode construction means that you get 2 preamp tubes for the price of one.
The two preamp tubes don’t have a lot of audible variations. In fact, even their differences are hard to identify in practice. After all, they’re made by the same company in the same period.
Can You Swap a 12AX7 Preamp Tube for a 7025 Tube?
As you can see, the two preamp tubes are almost identical in every way. The only difference between the two is the lower hum and noise that the 7025 preamp tubes produce.
However, the 12AX7 doesn’t produce a lot of noise compared to other preamp tubes. This means that you might not be able to pick the difference between the two.
Yet, they both have the same 9-pin design. So yes, you can swap a 12AX7 preamp tube for a 7025 tube and vice-versa.
There you have it. A complete comparison between 7025 tubes vs. 12AX7 one. Apart from the label, you might not be able to tell the difference between the two.
Both preamp tubes are 9-pin tubes with dual tripodes that have high voltage. The 7025 produces a lower level of noise and hum compared to the 12AX7.
On the other hand, the 12AX7 is reliable and more affordable with little to no noticeable differences.