The Bellari PA555 Preamplifier. I’m going to get right to the heart of the matter and tell all of you that the Bellari PA555 Preamplifier doesn’t just sound “good for the money.” The PA555 sounds “good for any amount of money.” The PA555 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.