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Blog posts tagged with 'PULLING A VACUUM'

CATHODE RAY TUBE PUMPING

Once sealing was completed, the cathode ray tube was passed to the pumping machine which comprised of a rotary carousel having a separate vane pump for each tube.  The tubes were mounted as you can see in the photo below and the tube pumping spigot was connected to a reinforced vaccuum hose and pumping was commenced: -

 

The pumping machine indexed and hence automatically carried the tubes through a tunnel furnace where they were strongly heated for 90 minutes to help drive off air and other gaseous components from the interior as well as to convert the faceplate phosphor from the carbonate salt to the corresponding more luminescent oxide salts. The level of vacuum was checked by measuring the ion current within the tube and once satisfactory, the getter material was flashed  by application of  an RF inductive heating pulse.

The final pumping operation was to seal off the pumping spigot and this was done by the application of a gas air flame as close to the tube neck - pumping spigot join as possible.  Gradually, the glass softened and as the tube was lifted from the pumping machine the glass parted leaving a full seal as a 'pip' which in a finished tube would be concealed under the bakelite base cap.