The 12AT7 is dual triode with gain of 70. It was the first double triode with noval socket and was originally designed by Valvo / Philips in 1951 for radio-frequency applications. Because it was used by Fender in many of its popular push-pull guitar amps as the phase-splitter section, it became a common in guitar amplifiers. The most common type (with the VF1 code) was made by Siemens in Germany. It is still made by JJ Electronics in Slovakia. European name: ECC81.