6X5GT military grade vacuum tube produced by RCA for the American Navy & Army in the Month of March 1955, so close to 70 years old at the time of writing this description (May 2023),

The 6X5GT is used as a rectifier tube in a wide range of audio products, e.g. the Leben RS30-EQ RIAA and various DAC's (Digital Audio Converter) from Audio Note UK.
Keyword(s): 6X5GT.