The HIGHGRADE Selection is the tip-of-the-top quality with lowest noise (microphony, hum, hiss) level. Typically only 1-5% out of the whole production yield make it to meet the HIGHGRADE requirements. Especially this low-noise tube is recommended for best clean tone with big bottom, warm midrange and silky top end. Performs great for HiFi too! Replaces any 12AX7A/WA, ECC83, 7025 etc. The TAD 5751 HIGHGRADE is the first choice for vastly improving the clarity, smoothness, and vintage tone character of most guitar amps! It still has plenty of gain so if you have a high-gain preamp that does not have that classic crunch characteristic, the 5751 tube will work wonders. In hifi preamps and CD players, the TAD 5751 HIGHGRADE will lower noise floor and sound smoother and clearer in place of many 12AX7 tubes.