Also known as ECC83, the 12AX7 preamp tube was originally engineered and manufactured by RCA electronics company. Nowadays, a variety of companies produce 12AX7 preamp tubes including JJ Electronics in Slovakia and Shuguang in China, commonly referred to as Groove tubes.
If you own a tube amplifier or considering using one, then you probably already know how crucial a 12AX7 preamp tube can be in your setup. Depending on the amp’s design and the number of gain stages it includes, you can get a wide range of tones from sparkling clean and mellow bluesy all the way to raging metal and everything in between. This 12AX7 datasheet is here to help you understand the deep inner workings of this famous tube.
What are 12AX7 Preamp Tubes?
Tube amplifiers use vacuum tubes that basically look like light bulbs with a pointed protrusion on the top. Vacuum tubes are made of glass that’s sealed with no air inside. These tubes are present in a couple of different types inside the tube amplifier, such as preamp tubes and power tubes.
Each tube type serves a specific purpose, all of which work together to create the guitar’s final tone. Preamp tubes contour and condition the general properties of the incoming signal (distortion or overdrive), while power tubes control the output of the amplifier.
Almost every tube amplifier out there (Fender, Marshall, Vox, Mesa Boogie, Peavey, and many others) includes at least one and up to five 12AX7 preamp tubes.
The first gain stage of a preamp tube is when you hit it with a substantial current (for example, from an active pickup or a pedal) to produce richer harmonics, sustain, and distortion. Some tube amplifiers feature two, three, and up to four gain stages. This is referred to as cascading gain stages.
12AX7 Datasheet: A Breakdown
Both 12AX7 preamp tubes are made the same way. Each one is a 9-pin miniature, high-mu, twin triode. Here’s what this means:
The 9-pin miniature part refers to the type of socket where you’ll be plugging the tube. It consists of nine fine pins arranged in the shape of a circle with a diameter of approximately half an inch. To make sure that the tube can be plugged in one way only, there’s a wide gap between pin number 1 and pin number 9.
The high-mu part corresponds to the amplification factor, which is abbreviated by the Greek letter μ (mu – it’s pronounced as ‘myoo’). It refers to the general amplification category of this preamp tube as opposed to other kinds of preamp tubes such as the 12AU7 “medium-mu”.
As for being twin triode, this means that each preamp tube carries two identical triodes inside its structure. A triode consists of three electrodes (plate, grid, and cathode), and it’s the most basic tube configuration for signal amplification.
Characteristics And Typical Operations
Class A Resistance-Coupled Amplifier
Average Plate Characteristics
Average Transfer Characteristics