From what I read in the GE data sheet both can be run from a 12.6 volt supply (series connection) or 6.3 volt (parallel connection). Which is what I already knew. The stated advantage to the 12AX7-A is that its use is advantageous in applications that require low hum and microphonic output. Text: "Ei-RC" - Electronic tubes factory Data Sheet Page 1 of 4 ECC82 /12AU7 ECC82 is A.F. Double Triode Quick reference data · · · Anode current Ia=10,5mA Transcoductance S=2,2mA/V , Electronic tubes factory Data Sheet Page 2 of 4 ECC82 /12AU7 Dimensions and connections Base: Noval , "Ei-RC" - Electronic tubes factory Data Sheet Page 3 of 4 ...

The TELEFUNKEN Elektroakustik ECC82-TK is a newly manufactured and cryogenically treated rendition of the classic ECC82, commonly known by the American designation 12AU7. The ECC82 is a dual triode vacuum tube with medium gain and low noise characteristics, making it ideal for hi-fi audio equipment and instrument amplification. Where the Telefunken smooth-plate excels, in my experience, is a certain band of high-mids that no other 12AX7 type hits without also having piercing treble. I've found another sonic aspect of 12AX7 performance to be very important: harmonic content. This is a kind of distortion, even if the amp does not sound overdriven.