12AX7 also known as ECC83 , is a family of vacuum tubes. There are miniature low-frequency double triodes with a high voltage gain and low slope of the transfer characteristic.
In addition to the original 12AX7 and its improved European version ECC83, the family includes more than 200 options. The electrical characteristics of most of these vacuum tubes are identical. More than that, if we are speaking about 12AX7 vacuum tube it became synonymous with ECC83.
12AX7 and ECC83 combined, became the most used tube to amplify low-frequency voltage. They absolutely dominated the American and Western European household appliances of the 1950s and 1960s. By the end of the 1980s, the production of 12AX7 ceased, but in the 1990s it was resumed in China , Russia , Serbia and Slovakia. The main application of 12AX7 in the 21st century is tube guitar amplifiers .
A little history of 12AX7 Vacuum Tube
In March 1948, a new miniature vacuum tube appeared in the catalogs of the American companies RCA and Sylvania, a double triode for industrial automation devices which was named 12AX7. 12AX7 was developed by RCA, and was contracted at Sylvania factories. Companies did not have any particular hopes for the new tube. It wasn’t even worth a note in the corporate RCA magazine. The designers only combined two triodes in one cylinder, identical to the triode section of the previously released 6AV6 diode-triode vacuum tube .
12AX7 Datasheet (Sylvania)
The combination of a high gain and low noise level embedded in the 6AV6 design turned out to be in high demand by the manufacturers of high-quality sound equipment and analog computers. So they have made the upgrade to 12AX7 Vacuum Tube . The main factor behind the unexpected success of 12AX7 was the release of long-playing recorders and players with low-sensitivity magnetic pickups into the US market. Mass equipment manufacturers urgently needed a low-cost, high-gain tube suitable for use in phono stage. Demand grew so rapidly that in 1952, five corporations were already releasing 12AX7: CBS , GE , National Union, Sylvania and Tung-Sol.
In the first years of production 12AX7 Vacuum Tube was clearly inferior in sound quality to its predecessor, 6SL7. Despite this, the 12AX7 replaced the “obsolete” 6SL7 and by 1956 it became the de facto industry standard for American market. The non-linearity of 12AX7 did not stop this. The designers of the 1950s were able to correct the flaws of the tubes with negative feedback . Therefore, 12AX7 found a place in the professional (tape recorders Ampex ) and in household equipment, and in guitar amplifiers, also.
Nowadays, 12AX7 and its European counterpart ECC83 are the most common tubes in the circuitry of guitar amplifiers. The choice of manufacturers is determined by the economy (12AX7 is still available and therefore available at affordable prices and conservatism. Most modern amplifiers are built according to proven schemes from 1950s. Leo Fender and other designers chose 12AX7 not by chance. The characteristics of this particular vacuum tube were ideally suited for systematic operation in the input overload mode and amplitude limits.
The decline of 12Ax7 Vacuum Tube
In the 1960s, the slow fading of the vacuum industry began. The first, back in the 1960s, the American Tung-Sol and CBS left the market. Telefunken Vacuum Tubes production quality has declined. The company began to sell under its own name products of other factories that differed from the original in high noise and high unwanted feedback effect. Other European companies have also switched to reselling mediocre Japanese vacuum tubes. Only Amperex and Mullard maintained the quality of ECC83 until the 1980s. In the late 1980s, we assist at the end of production for GE, RCA and Sylvania (bought by Philips). Sophisticated automated equipment, entire plants designed to produce millions of tube annually was lost forever. It is only known for certain that the Mullard production line, on which the CV4004 military was produced, ended up in China and Amperex went in Yugoslavia.
In the last quarter of the 20th century, the demand for 12AX7 and ECC83 was supported by millions of guitarists still using tube amplifiers. The exact size of the market is unknown. In 2000, it was estimated at at least one million tubes per year. Until the mid-1990s, demand was satisfied from old stocks. The American market was swept by a wave of substandard tubes, pretending to be high-quality. Unscrupulous dealers marked with fake brands Amperex, Mullard and Telefunken all 12AX7 that they could get. As the American and West European stocks are exhausted, low-quality Japanese, East European, and even Indian tubes went into action.
By 1995, there were four 12AX7 / ECC83 production facilities left in the world: EI Tubes Serbia, Sino (China), Tesla (Czech Republic), and the Russian Reflector plant which began producing three structurally different versions of 12AX7 on request American wholesalers. All these tubes were inferior to the West European ECC83. the Chinese ones had a short service life, the Serbian ones had an increased feedback effect, the Russian ones had an increased distortion like the old American 12AX7. By 2000, the Chinese plant stopped production, and the plant in Serbia, despite the international embargo , survived and managed to improve the quality of the tubes. From 2010 Russian-made tubes were sold in the United States under the brands of local dealers and under the classic brands of Genalex Gold Lion, Mullard, Tung-Sol.