If this is true then the carbon in charcoal briquettes would slowly combine with the O2 in the air, form CO2, and eventually vanish - quite literally - into thin air. • Rich, ag6k .
They do, but it's a VERY slow process at temperatures comfortable to humans and other living things. At high enough initial temperatures, in a 21% oxygen atmosphere, the heat of oxidation is sufficient to cause the briquettes to remain at a dull red incandescence until they do indeed disappear "into thin, hot air!
The process doesn't work as well at high vacuum however, the charcoal/graphite just hangs around, and at high oxygen concentrations (e.g. when LOX is poured onto the briquettes -- Kids: DON'T try this at home, go to someone else's house instead!) w/ an ignition source present (e/g/ a burning cigarette within the briquette pile) one only has a couple seconds of cooking time before new briquettes were needed!
There was one type of high power tube ( 50 - 100kW out) that didn't have a getter. This form of tube was called a 'demount', short for demountable. It was permanently on a vacuum pump, and was water cooled. When the filament failed, they turned off the vacuum, undid a couple of screws and took the thing apart, fitted a new filament (if it had arced, a new grid) and pumped it down again...
If I recall from a tour a few years back, one (or more) of the VHF (UHF?) TV transmitter tubes at Cedar St in Needham (Boston), MA were bolted together, water/glycol cooled units. Not sure what the vacuum source was. One of the transmitters was an air cooled solid state (Harris?) unit too. Lots of big copper coolant tubes to outside radiators, 8" copper coax hard line all over the place, and copper ground bus bar running around in that installation -- combined w/ the 1300' +/- tower that would make one heck of a VHF/UHF weak signal contest station, though I wouldn't want to climb the tower!
(On a more somber note, a tower worker recently fell to his death from another TV/FM tower, just across the highway (Rte 128); an investigation is ongoing. Lets be be VERY careful out there, whether climbing towers, working with amps at High Voltage, making charcoal disappear or whatever!
KB1LKR -- Steve