Ultra low noise thanks to unique spiral filament which eliminates cathode-to-filament induced hum (common on amplifiers that use AC on the filaments)</br>Best all-around choice & best value</br>Single tube</br>ECC83/7025 equivalent</br></br>Product Description</br></br>High gain Twin Triode short plate format?? with detailed?? musical tone. Most popular  replacement for all circuits requiring 12AX7/ECC83 types.</br><br/>http://www.amazon.com/gp/product/B0002M72JS