[Marcel]’s amplifier also uses a PY88 tube rectifier instead of semiconductor diodes, making it an entirely silicon-free design. Although [Marcel] hasn’t posted up detailed build instructions ...

Conversation evolved into bloviation on what our cover art would look like, certainly it would be a photo of our battery powered tube mic pre-amp recently ... that heats up a cathode metal plate ...

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 ...