GT-12AU7

These are commonly used as phase inverters in McIntosh Hi-Fi amps, some Ampeg amps, and will yield the most clean headroom in many amps.

In the latest Fender Pro Series amps such as the Pro Reverb, Concert, and Twin, this tube in V2 (or a 12AY7), will drop the gain of the gain channel where some feel the tone is of a less intense or “buzzy” character. This will then allow a much wider range in the sweep of the volume and gain controls of this channel.