Gradual build-up of darkish coating on power triodes

Tubes Asylum

Questions about tubes and gear that glows. FAQ

Quick question:

What is the nature of a gradual darkening on the inside of the glass tubes where the filament is not covered by the plate? I have seen this on the 6C19Pi triodes as well as on the TJ 300B/n so-called mesh-plates. The 6C19Pi shows up as a vertical band where the filament is open to the glass. On the 300B's it makes more of a soft mimicking of the mesh plate. None of my other power tubes show this as the plates cover the anode/grid assembly completely.

Just wondering what the nature of this is. Am assuming it is a sign of age as well as evidence of the cathode losing mass.

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Topic - Gradual build-up of darkish coating on power triodes - mhardyman 17:51:54 07/08/12 (3)

RE: Gradual build-up of darkish coating on power triodes - Alpha Al 12:20:17 07/10/12 (1)

RE: Gradual build-up of darkish coating on power triodes - mhardyman 13:12:30 07/10/12 (0)

Check your filament voltage - Chris O 07:27:46 07/10/12 (0)

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