The JJ ECC83s (12AX7) is a high gain preamp double triode valve. thanks to its design it performs with very low noise and microphonics. Harmonically rich with a detailed low end and a warm high end.These tubes are immediately discernible from other 12AX7. This construction makes them very rugged and reliable. This is one of the best new 12AX7 for any guitar amp. It is very musical – rich with great harmonics. An excellent tube in all Marshall amps in the three preamp positions.