In large tubes, that require a hoist to pull them from the socket, we
either us DC on the filament or use a specially shunted transformer
as has been discussed before. The manufacturers have been keen to
advise us about mechanical vibration of the filament which can break
it. Use of SCR or Triac phase-controlled AC is not advisable. Ever
listen to a lightbulb which is contolled by a dimmer?
Since a special transformer must be wound anyhow, it is simple to ask
the supplier to set it up to be current limited to 2 x the normal fil
current. This takes care of the cold filament inrush current, and
actually makes the transformer sloppy.
Perhaps the use of phase controlled AC is ok for smaller tubes with
and without handles?
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