ECC83-TK (12AX7) Black Diamond Series Vacuum Tube

TELEFUNKEN Elektroakustik Black Diamond Series Vacuum Tubes are manufactured in partnership with JJ Tubes of Slovakia. The new production tubes are designed to be harmonically rich and tonally balanced. Each tube is rigorously tested, cryogenically treated and extensively burned-in.

Developed by RCA and released in September of 1947, the 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 12AX7 compact, relatively inexpensive, and produces a high quality full frequency response.
Being a triode design, the most common artifact found from 12AX7's is even order harmonic distortion when the tube is driven into "overdrive". Even order harmonics fit into the western musical scale and are not generally perceived as "harsh" or "unmusical". The 12AX7 is also known as the ECC83, which was the European designation found on tubes from Phillips / Mullard.