On: Making glass-to-metal seals for home­made vacuum tubes

[tliltocatl]

If you want a gas discharge tube and not vacuum, you can even drop the coil on the inside: https://hackaday.io/project/194683-plasma-toroid-sky-guided-...

But most hollow-state devices run on either DC or pulses, so coupled inductors wouldn't work.

[smlacy → tliltocatl]

Wouldn't work ... without additional electronic components.

[tliltocatl → smlacy]

Than you can skip the hollow state part altogether. And any plastic-package parts would screw your vacuum up badly - if it survives sealing and bakeout that is.