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12AX7 (also known as ECC83 [1]) is a miniature dual-triode vacuum tube with high voltage gain. Developed around 1946 by RCA engineers [ 2 ] in Camden, New Jersey , under developmental number A-4522, it was released for public sale under the 12AX7 identifier on September 15, 1947.
The IIA and IIB, and some late-model Mark I amps, used a JFET-based device called fetron in place of the input stage 12AX7 (V1), and included a switch for configuring the amp for either Fetron or 12AX7 operation. The reason for using a fetron was to address some of the problems associated with microphonic 12AX7 tubes in a high-gain situation ...
Tube sockets are electrical ... United States and most of the European tubes, e.g., 12AX7 ... the lighthouse tube, both solving the same problems but with ...
Philips continued to improve and enlarge the tube plant in New York, but also used the Amperex name to distribute their new line of Dutch-made miniature tubes, (12AX7, 12AU7, 12AT7) to feed the booming U.S. hi-fi market. Classic hi-fi brands such as Marantz, Fisher, and H. H. Scott, Inc., used these tubes.
The typical flashed getter used in small vacuum tubes (seen in 12AX7 tube, top) consists of a ring-shaped structure made from a long strip of nickel, which is folded into a long, narrow trough, filled with a mixture of barium azide and powdered glass, and then folded into the closed ring shape. The getter is attached with its trough opening ...
It was released as a response to the extensive number of modifications that were being applied to the regular Valve Junior. The circuitry was altered to include a second 12AX7 preamp tube, a gain control, and a spring reverb in addition to the single volume control, as well as a standby switch to preserve tube life. Thanks to a dual function ...
The most significant difference between the two is that 6N2P has its two filament elements connected in parallel, unlike the series filament connection of the 12AX7, and it is thus only possible to operate it from a 6.3 volt, 340 mA filament supply (whereas a 12AX7 may be operated from either 6.3 or 12.6 volts, at 300 mA or 150 mA, respectively.)
Vox soon tired of the problem so to cure AC30/4 reliability issues caused by the troublesome EF86 preamp tube, [4] in late 1960 Vox redesigned the preamp circuit, replaced the EF86 with an ECC83 (12AX7), and released this new design as the AC30/6. The AC30/6 was now an amp with three channels, each channel having two inputs.