9 Nov
2007
9 Nov
'07
12:17 a.m.
On 9 Nov 2007 at 2:28, der Mouse wrote:
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.)
Interesting idea, but why not a simple copper cathode extending
through the (silica) envenlope and heated externally? Thermal
conduction should give you enough for thermionic emission on the
interior. I wonder if it's already been done--as a high-temperature
measuring device.
On the subject of cathodes (and vintage computers), whatever happened
to the tunnel cathode? Back in the 60's, there was a lot of work
(some by IBM) going on with CRTs utilitizing them and there were
predictions that tunnel-cathode tubes in general would make electron
tubes as reliable as the transistor.
Cheers,
Chuck