Most power tubes use a "directly heated" filament as the cathode, also known as the " thoriated-tungsten filament." The major reason for the use of the thoriated-tungsten filament in power tubes is because it is more tolerant to ion bombardment than the oxide coated emitter. Example tubes are the 813, the 811, the 572B, 3-500Z, etc.
The "Indirectly Heated," or "Unipotential," or
oxide coated emitter has the construction whereas an electrically insulated heater is inside a nickel-alloy cylinder and coated with barium-strontium oxides. It is sometimes denoted as the "any position,” or “dark cathode” tube. The major advantages of indirectly heated cathodes are higher electron emission efficiencies at lower temperatures, and reduced hum modulation of the space charge. Examples of indirectly heated cathodes are the 807, the 6146, 4D32, and most receiving tubes.
If the filaments are subjected to overvoltages for a short time this might boil off some oxides - of course assuming the tube still has a vacuum.
I did not read the QS? article.
Phil - AC0OB