12AX7. High-Mu Twin Triode. 9-PIN MINIATURE TYPE. GENERAL DATA. Electrical: Heater, for Unipotential Cathodes: Heater arrangement. Series Parallel . Resistance – coupled amplifer cathode grid bias. Limiting Values: Ua = V. Wa = 1 W. Ik = 8 mA. Ug = V. Rg = 2,2 MΩ. Uk/f = V. Rk/f = kΩ. 12AX7. 12AX7 Application Data. Class, Va, Vg1, Ia, Ra, S. Triode, , -1, , 80,, Triode, , -2, , 62,, 12AX7 Data sheet links.
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It was released for public sale under the 12AX7 identifier on September 15, The 12AX7 was originally intended as replacement for the 6SL7 family of dual-triode amplifier tubes for audio applications. It is popular with tube amplifier enthusiasts, and its ongoing use in such equipment makes it one of the few small-signal vacuum tubes in continuous production since it was introduced.
The 12AX7 is basically two of the triodes from a 6AV6 – a double diode triode.
The 6AV6 is a miniature repackaging with just a single cathode of the triode and twin diodes from the octal 6SQ7 a double-diode triode used in AM radioswhich itself is very similar to the older type 75 triode-diode dating from As of [update] the 12AX7 was made in various versions by two factories in Russia Winged C, formerly Svetlana, and New Sensorwhich produces tubes under the Sovtek, Electro-Harmonix, Svetlana, Tung-Soland other brands for which the firm has acquired trademark rightsone in China Shuguangand one in Slovakia JJ Electronicfor a total annual production estimated at two million units.
The vast majority are used in new-production guitar amplifiers or for replacements in guitar and audio equipment. The 12AX7 is a high-gain typical amplification factorlow-plate-current triode best suited for low-level audio voltage amplification.
In this role datasneet is widely used for the preamplifier input and mid-level stages of audio amplifiers. It has relatively high Miller capacitance, making it unsuitable for radio-frequency use. Typically a 12AX7 triode is configured with a high-value plate resistor, k ohms in most guitar amps and k ohms or more in high-fidelity equipment.
Grid bias is most often provided by a cathode resistor. If the cathode resistor is unbypassed, negative feedback is introduced and each half of a 12AX7 provides a typical voltage gain of about 30; the amplification factor is basically twice the maximum stage gain, as the plate impedance must be matched.
Thus half the voltage is across the tube at rest, half across the load resistor. The cathode resistor can be bypassed to reduce or eliminate AC negative feedback and thereby increase gain; maximum gain is about 60 times.
TDSL Tube data [12AX7]
The initial “12” in the designator implies a volt heater requirement; however, the tube has a center-tapped heater so it can be used in either 6. The 12AX7 is the most common member of what eventually became a large family of twin-triode vacuum tubes, manufactured all over the world, all sharing the same pinout EIA 9A. Most use heaters which can be optionally wired in series They span a wide range of voltage gain and transconductance.
Different versions of each were designed for enhanced ruggedness, low microphonicsstability, lifespan, etc. In European usage special-quality valves of some sort were often indicated by exchanging letters and digits in the name: In the US a “W” in the designation, as in 12AX7WA, designates the tube as complying with military grade, higher reliability specifications.
The ‘E’ in the European designation classifies this as having a 6. It can, of course, be wired for operation off either voltage.
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Kit Building 101
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12ax7 Tube Datasheet – GuitarKitBuilder