Here’s a broken EF40 pentode tube. I dropped it, so took the opportunity to take a peek inside. The construction is intricate and quite beautiful.
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| Inside the EF40 tube, glass envelope removed |
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| EF40 pentode with screen removed |
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| EF40 with getter, mica insulation and plate removed |
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| EF40 showing grids heaters and cathode |
Vacuumtubes.net have a good description of how tubes work, and this diagram from shows all the parts:
