The 12AX7 is the single most important signal preamp tube. PM tubes are built to the highest possible standard and have extra screening to eliminate microphony (squeal) and excessive white noise. The PM-12AX7LM (LOW MICROPHONY) will replace the same tube as the 12AX7A but is the better choice for critical position in your amp. It has been specially selected for it's low noise levels and will give a very warm "classic" European sound.
