There are a couple of reasons I suspect it's taken this long to see a vacuum tube in a pair of headphones. Tubes are hungry ...

Solid-state tube ... in your guitar amplifier. Unlike their fragile tube counterparts, these replacements utilize semiconductor technology to emulate the tonal characteristics of vacuum tubes.

There’s a mystique among both audiophiles and musicians about vacuum technology, thus having a tube amp still carries ... The design is inspired by the guitar amps of the 1950s and 1960s so ...