gasified valves

By valve, are you referring to vacuum tubes? The deposit sounds Rilke the getter, if it's white instead of silver that means air has got in the tube.

It could also be evaporated material from the cathode deposited on the inside of the glass, that will form wherever there's a clear path from the cathode to the glass.

on

Most tubes commonly in use have a Barium getter. This material is vaporized within the tube during the manufacturing process to absorb any loose gas molecules within the tube. When the tube cracks or loses its seal, the Barium oxidizes quickly, thereby turning white (Barium Oxide).

There are other getter materials used, but Barium is far-and-away the most common.

Peter Wieck Wyncote, PA

Oxidized mercury?

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Oxides of Mercury are red or cinnamon in color, and turn skin or other semi-absorbant surfaces black. Interestingly enough, many compounds including mercury are similarly colored. The common mercury ore form is called "cinnabar" for that reason, even though it is mercury sulfide.

Peter Wieck Wyncote, PA

Hmm, don't know?, could be the heater falling apart? could be the results of the getter used to remove the remaining Oxygen.

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By far the msot common is the getter. Why is it usually on top? Because that's where the original metallic barium or other highly reactive material was placed during manufacture. Sometimes it's on the side or near the base. But since it's a metal and conductive, has to be placed away from an area where it could short between pins.

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I'd thought that was silvering to block stray electrons or something firing out of the tops of the tubes. I'd thought this whitening process was some sort of safety/failure indicator process as a visual indication of a mechanically failed valve. Still learning even if an ancient technology

metal oxides

NT

OK... let's start at the beginning.

"Getters" are usually alkaline-earth metals flashed onto the inside surface of the tube during the manufacturing process by a number of mechanisms that are not terribly relevant, but include inductive heating, a high current and voltage applied to a pellet of the candidate metal that vaporizes it or any of several other mechanisms.

These getters are to "get" stray molecules of gas that may remain in the tube from the manufacturing process. So, they are going to be very 'active' metals.

Far-and-away the most common getter past and present is Barium. Others include Aluminum, magnesium, and any of several other materials or alloys. Very high-temperature tubes use somewhat less-active getter- metals as the temperature overcomes the otherwise limitations of the metal and permits greater life and less volatility of the getter.

Typically the getter is flashed to the sides and top of the tube for reasons already noted.

When the tube envelope fails, the getter very rapidly combines with available oxygen and other elements in the air. Barium turns white. Aluminum turns white, Magesium turns white. This designates an envelope failure. The tube will be worthless even if the filament survives by some miracle.

There are some gas-type tubes and rectifiers that use vaporized mercury that have no 'getters'.

There is a lot more out there on this subject, but this should suffice for now.

Peter Wieck Wyncote, PA

There's nothing that can fire out the tops of the tubes, a very few HV rectifier tubes can emit trace amounts of x-rays, but the vast majority of tubes operate at far too low a voltage for this. Electrons can't travel in free air even if they weren't blocked.

When Electrons travel in free air, they are called "ionizing radiation" and cause all sorts of havoc. AKA Photoelectric-effect Gamma Radiation.

Peter Wieck Wyncote, PA