The Hewlett Packard 2AX7, also known as the ECC83, is a dual triode vacuum tube with high voltage gain. It was developed by RCA engineers in 1946 and released for public sale under the 12AX7 identifier on September 15, 194Originally intended as a replacement for the 6SL7 family of dual-triode amplifier tubes for audio applications, the 12AX7 has become a popular choice for guitar tube amplifiers and is one of the few small-signal vacuum tubes in continuous production since its introduction.
History
The 12AX7 is essentially two triodes from a 6AV6, a double diode triode. The 6AV6 is a miniature repackaging of the triode and twin diodes from the octal 6SQ7, which is similar to the older type 75 triode-diode dating from 1930.
Application
The 12AX7 is a high-gain, low-plate-current triode that is best suited for low-level audio voltage amplification. It is commonly used for the preamplifier stages of audio amplifiers, including the input and mid-level stages. Due to its relatively high Miller capacitance, it is not suitable for radio-frequency use.
In typical configurations, a 12AX7 triode is paired with a high-value plate resistor, usually around 100 kohms in guitar amps and 220 kΩ or more in high-fidelity equipment. Grid bias is typically provided by a cathode resistor. If the cathode resistor is unbypassed, negative feedback is introduced, and each half of the 12AX7 provides a typical voltage gain of about 30. The cathode resistor can be bypassed to reduce or eliminate AC negative feedback, thereby increasing gain. The maximum gain can reach about 60 times with a 100k plate load and a center-biased and bypassed cathode.
The 12AX7 has a center-tapped heater, which allows it to be used in either 3-V or 16-V heater circuits. It is the most common member of a large family of twin-triode vacuum tubes, all sharing the same pinout. Other tubes in this family include the 12AT7, 12AU7, 12AV7, 12AY7, and the low-voltage 12U7, among others.
Hewlett & packard: pioneers in tech industryManufacturers
As of 2022, versions of the 12AX7/ECC83 are available from various manufacturers, including Electro-Harmonix and Tungsram.
The Hewlett Packard 2AX7, or ECC83, is a versatile dual triode vacuum tube with high voltage gain. Its history dates back to the late 1940s when it was developed as a replacement for the 6SL7 amplifier tubes. Over the years, it has become a popular choice for guitar tube amplifiers and is still in production today. Whether you're a musician or an audio enthusiast, the 2AX7 can provide the high-quality audio amplification you need.