Mesa/Boogie most frequently used their premium house-brand 12AT7 preamplifier tube as a reverb driver in the Studio Preamp and a handful of Mark series amplifiers. Today, you'll also find this tube stock in their Triple Crown TC-50 and TC-100 amps. The Mesa/Boogie 12AT7 is a premium-grade, classic low-gain preamplifier tube — one that was also commonly used as a phase inverter in older amplifiers. If you want to keep your amps playing and sounding their best, stock up on Mesa/Boogie 12AT7 preamp tubes from Sweetwater. Sold individually.