“Vacuum radio tubes ran cooler filaments than light bulbs; and, still evaporation from the filament deposited a black layer inside the glass. Argon gas reflects some of the lost tungsten back to the filament, and lengthens the light-bulb life accordingly; but, interferes with operation of a radio tube and is not used in that instance.”
That’s not correct. Radio tubes do not use argon or any other gas. The only exception to that are thyratron tubes and very old voltage regulator tubes. Normal vacuum tubes are evacuated to around 1X10 to the minus 5 torr, then a getter is fired to burn off and/ot trap any gasses that are left.
They run under a very hard vacuum. I know this because I’ve built them in my shop. The vacuum equipment is very expensive. You need a roughing pump and either a diffusion pump or a turbo vacuum pump.
Incandescent light bulbs do not require near as hard a vacuum BTW.
“Vacuum radio tubes ran cooler filaments than light bulbs; and, still evaporation from the filament deposited a black layer inside the glass. Argon gas reflects some of the lost tungsten back to the filament, and lengthens the light-bulb life accordingly; but, interferes with operation of a radio tube and is not used in that instance."
Have you by chance considered building a Farnsworth Fusor?