Fun with Geissler tubes


Posted on Feb 6, 2014

A box full of Geissler tubes and a Ruhmkorff coil. He said his grandfather built the tubes by blowing the glass around 1900, more than one century ago! He wanted to see if the tube still worked, but a first attempt of powering them with the original Ruhmkorff coil failed. Than, we tried with a CCFL (Cold Cathode Fluorescent Lamp) lamp driver circuit found in an old laptop computer, but this


Fun with Geissler tubes
Click here to download the full size of the above Circuit.

failed as well. At that time, we had no idea of the voltage required to strike the tubes and, of course, we didn`t want to break or blow up these precious tubes with too much power. So we decided to buy a brand new Geissler tube (yes, they are still manufactured) and designed a dedicated power supply. A Geissler tube is the ancestor of the modern neon sign tubes commonly used for advertising. Today it`s mainly a decorative glowing object, a scientific curiosity and a nostalgic souvenir of the past. It`s composed by a sealed glass tube of any shape, usually between 10cm and 1m in length. It has two electrodes, one on each end, while the interior is evacuated and filled with a low pressure gas (something like 1mbar). A current flowing from the electrodes through the gas make the gas glow and fluorescent materials used to build the tube glow as well. The gas determines the color of the glow: air will glow bluish, neon will glow red, hydrogen will glow pink, and so on. Some elements are often added to the glass to make it also glow and determine its color: the most common is uranium glass that glows yellow-green. Sometimes Geissler tubes are mounted inside bigger glass tubes filling the space in-between with glowing powders or liquids. Sometimes, special targets can be found inside the tube for some more special effect (see the picture section below ). As common neon tubes, Geissler tubes requires a high striking voltage, and...




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