The Groove Tubes SAG-AT7-MPI Matched Phase Inverter Retube Kit contains specially selected and matched 12AT7 vacuum tubes for critical audio or guitar/bass amplifier use. Intended when a match of the two sides of the triode are desired for phase inverter or driver use.

This 12AT7 tube is a dual triode where the A and B sides are closely matched for use in critical high end audio applications or for use in the phase inverter or driver position of musical instrument amplifiers.

The benefit of this Groove Tubes vacuum tube in a guitar or bass amplifier is a matched output section. At lower frequencies such as dropped tunings, 7 string guitars, or bass guitars, the upper and lower portions of the output waveform will be much more equal. When this waveform is not equal, differences are cancelled out in the NFB loop of class A/B amplifiers and are noticed as a lack of sustain or apparent "dead spots" in areas of the fret board.

At high levels at all frequencies, sustain will be improved. This is even more critical in Class A amplifiers such as the Vox AC-30 and Matchless amplifiers.

Use this MPI in any application where a phase inverter / driver of the ECC81/12AT7 tube is specified. The phase inverter / driver position of a guitar or bass amp is a current driving position, and not part of the tone generation stage. These tubes are selected for specific characteristics, so they may be a 12AT7A, 12AT7C, or other 12AT7 tubes.

Use of a 12AT7 in place of a 12AX7 will yield more clean headroom in your output section. The two tube types are interchangable without any adjustment required, so feel free to experiment!

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