The Burn-Hole Club

The coils that provide the magnetic force to move the electron beam

Cathode ray tubes are a remarkable technology that incorporate many seemingly magic principles of physics.  Thermionic emission causes electrons to “boil” off a cathode, high voltage electric fields accelerate and focus them, and magnetic fields steer them to the anode screen where they energize phosphor molecules, which then re-release that energy as visible light!

While developing the electronics to control the CRT and make all this magic happen, we often had to “bring up the spot”, showing the electron beam in one static location, where it could be examined visually and measured with various instruments. 

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Cathode Rays

The 100th anniversary of the cathode ray tube.

This is the first of three posts describing a now-(nearly)-obsolete technology.

Thomas Edison nearly discovered them.  In his experiments with heated filaments in evacuated glass bulbs trying to find a suitable incandescent lamp, there were hints.  He noticed depositions of material on the walls of the glass tubes.  Many scientific discoveries are preceded not by the expression “Eureka”, but instead by the comment: “Hmm, that’s funny”.  If he had followed up on this odd result, he might have also invented the vacuum tube amplifier.

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