There are plenty of tube amplifiers now being manufactured, with a popular choice being headphone amplifiers ... in for the op-amp buffer role, making for a very simple circuit.

[NotionSunday] put together a hearing amplifier project ... it to a conventional headphone. The device is wired point to point, and is, perhaps, pocket-sized. The opamp circuit is simple.

Analogue headphone amplifiers are less common than they used to be thanks to the more fashionable DAC/headphone amp alternative dominating ... and it is a proprietary circuit that claims to improve ...