The TELEFUNKEN ECC83-TK is a well-balanced tube suited for all types of music and playing styles. Designed to allow for cleaner headroom than higher gain 12AX7s when pushed into overdrive, it offers distortion with strongly defined lows, a rich mid range and clean, smooth highs.
Developed by RCA and released in September of 1947, the ECC83-TK (12AX7) is a high gain / low noise tube that is the most popular tube used in input / inter-stage audio amplifiers. The dual triode design makes the ECC83-TK (12AX7) compact, relatively inexpensive, and produces a high quality full frequency response.
12AX7's are known for their rich even order harmonic distortion when driven into overdrive. Even order harmonics fit into the western musical scale and are more pleasing to the ear than the harsh odd order harmonic distortion created by transistors. The (ECC83-TK) 12AX7 is also known as the ECC83, which was the European designation found on tubes from Phillips / Mullard.
I am very happy with this. I get a new sound when I push the input harder. For some reason headroom is better.