Indicator tubes for transistor logic machines.

[der Mouse]

>> Forget electrcity ... Have a torch heated valve. :)
> I'd love to see you keep that flame burning while having a
> sufficienltly low gas pressure around the cathode to have a long
> enough mean free path for the electrons, Not to mention problems
> caused by the ions geenrated by said flame.

Doable.

The glass envelope for the vacuum takes the form of two concentric
cylinders joined at their ends, topologically a torus.  The cathode is
another concentric cylinder, this time of metal or whatever, just
barely larger than the inner glass cylinder, with the grids and
anode/plate forming successively larger cylinders.  The heater flame
passes through the centre of the cylinder (which is outside the glass
vacuum envelope), heating the cathode by infrared radiation, much as a
conventional heater does.  (The glass forming the inner cylinder needs
to be infrared-transparent and probably high-melting-point.)

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