The Bellari PA555 Preamplifier. uses a 12AX7 tube running at 150 volts. The input signal is connected directly to the grid of the tube and all of the gain of the PA555 is from the 12AX7 tube. The PA555 has a no feedback circuit or integrated circuits in the audio path, it is all analog. Box Contains Bellari PA555 Preamplifier Made in USA PA555 15V power supply PN PS27s Owners manual