I found a few tubes in stinging equipment and they have silver stains on the glass and even dark signals in these places. Are these tubes unburned? What are these spots?
In the process of manufacturing the valves, by vacuuming the inside, remaining gases may remain, such as oxygen that would attack the electrodes and the filament when heated. To avoid this problem, a small zirconium and barium-based metal ring is added to the inside of the valve, the purpose of which is to absorb oxygen when the valve is first turned on. This ring, called "getter" causes a silvering of the glass when it evaporates with the action of the remaining gases. The presence of this stain does not mean, therefore, that it is bad.
