Quote:
Originally Posted by Sandy G
I wonder if that great big, ginormous 30" tube was electrostatic, or magnetic, & if it was, maybe that's why it was so short lived... Always heard those things were kinda primitive & a bit crude, despite their huge sizes...
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The DuMont 30BP4 used electromagnetic deflection. DuMont did make electrostatic tubes up to 20", though.
The reason for the short life on 30BP4s was insufficient gettering. The tubes were not aluminized, so getters could only be used in the neck to avoid contaminating the phosphor with patches of barium. Unfortunately, neck getters alone weren't sufficient for a tube with that much evacuated volume and that many linear feet of glass to metal seal to potentially leak air molecules into the tube.
Once aluminized tubes became the standard, additional gettering could be used inside the funnel area to improve the vacuum integrity.