Glassblowing #2: Making a tungsten lamp and (bad) vacuum diode
A hobbyist documents making a simple incandescent lamp by sealing a tungsten filament inside a glass tube under vacuum, and experiments with a crude vacuum diode that shows poor thermionic emission performance due to trapped gases in the tungsten and the small anode area.
Background
- The author is a hobbyist glassblower and electrical experimenter, documenting a personal project to make functional vacuum tubes by hand — not a professional or company.
- This is Part 2 of a series. Part 1 covered the fundamental challenge: sealing metal wires through glass so they remain airtight and don't crack. This installment applies that skill to build actual devices.
- Incandescent lightbulbs work by heating a tungsten filament until it glows white-hot (~2500°C). In air, tungsten instantly oxidizes (burns up), so the bulb must be evacuated or filled with inert gas. Early vacuum pumps were unreliable; the Nernst lamp mentioned used a ceramic filament that works in open air.
- A vacuum diode is the simplest type of vacuum tube: a hot filament (cathode) boils off electrons, which are attracted to a positively charged plate (anode), allowing current to flow in only one direction. This rectification property made them essential in early radios and power supplies. The author's attempt is "bad" because it leaks and the anode is too small, so almost no electrons are collected.