The Siemens CV493 / 6X4 is a miniature full-wave rectifier vacuum tube designed for use in power supply circuits of valve-based audio and electronic equipment. Manufactured by Siemens, this valve is known for its high reliability, stable voltage rectification, and long service life.

The 6X4 (also known by the European designation EZ90) converts AC voltage from a transformer into DC voltage to power other valves within an amplifier or electronic device. Siemens-produced versions are highly regarded for their consistent build quality, low failure rate, and excellent durability.

The Siemens CV493 / 6X4 is often sought after for restoration projects and high-end audio builds, where dependable power supply rectification and authentic vintage components are required.