The Ruby 12AX7ACZ-HG is a high grade dual triode 12AX7/7025 preamp tube that is most suitable for high gain amplifiers where microphonics are a major concern.The 12AX7ACZ-HG is also ideal for use in combo amps where vibration can cause premature tube failure. It’s is a smooth sounding preamp tube delivering low noise under all conditions and great reliability.The Ruby 12AX7ACZ-HG High Grade is a re-labeled JJ ECC83. It’s the highest gain of all the 12AX7’s, loved by classic rock and heavy metal guitarists.