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Method of Repairing Valve Filaments

Experimental Wireless, July 1924, courtesy of the Journeaux Historic Wireless Collection.
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The figures illustrate a process of renewing the filament in valves such as the R type, where the filament is horizontal (British Patent 215,437 , J M Longe and P V Castell-Evans).

The pip is first removed to release the vacuum, and through the hole thus made at F air is forced in from the tube E, while the points C are heated with a pointed blow-pipe flame G. Two holes are thus burst in the glass at points C sufficient to allow the introduction of suitable manipulating tools.

The tops of the vertical portions of the filament supports D are cut off, and removed along with the remains of the old filament. New tops to these supports are made and fixed, as shown at H in the second figure, by forming their lower ends into helixes that will just fit over the remains of the old supports.

When in position, the helical portions are pinched to secure them firmly in position. The new filament may be attached to the tops of these new supports before their insertion in the valve. The holes at C are sealed up again, and the bulb is evacuated through the tube sealed on at F.

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