When trying to outfit a classic amplifier - whether a headphone preamp, a stereo amplifier, or the ultrapopular guitar amp - virtually every piece comes together to create a sound unique to each unit. From power tubes and preamp tubes to the rectifier, each adds its own distinct signature to the piece's overall musical landscape. Rectifiers can add notes of warmth and richness based on changes in current drop. That makes them essential for obtaining that sought-after vintage tone. The RCA 5U4G - as with most RCA tubes - is popular because of its excellent construction and reliability. It boasts an overall musicality, enhancing treble and mids without neglecting a deep and full bass. With the right setup, the 5U5G can also give you that much-desired rectifier 'sag' that really sets classic amps apart from any kind of modern-day sound.