Big bulb vintage rectifier tube, used in high-end audio amplifiers and also modern, recto-type amps, such as the Mesa Boogie Double/Triple Recitifer.
Its tone is smoother than that of a solid state rectifier. Substitute for the 5Z3P / 5Z3P-J or 5C3S rectifier tube like used in LABOGA Mr Hector Head. It can replace the 5U4GB.
CALIFORNIA PROPOSITION 65 WARNING