Light 13: Vacuum Tubes

By Circe -

Welcome to the 2023 Advent Calendar, which this year is just a list of things that light up all pretty. Previous entries are here. If you enjoy this and want to encourage me to bang more things out on a keyboard, consider supporting my Patreon, or sending something off of my Christmas list. If you'd rather support my spoiled pets, their Ratmas list is here. If you want to spend money but not on me, you can direct your donations to Mainely Rat Rescue, who handles rescue and foster operations for rats, mice, gerbils, guinea pigs, and other small mammals in the New England area, or the MSPCA, where my critters got their medical care before I found a good exotics vet, and where I picked up Koda and Yogi. 

Enjoy your trip through the cavalcade of things that go blinky-blink in the dark!

A pen-and-ink illustration of a rat examining a vacuum tube.
It's time for us to divert a little into a subject whose illuminating nature is a little less obvious: Vacuum tubes.

If you are not a restorer of old media technology -- or a hopeless audiophile hipster -- you probably have no idea what a vacuum tube is. The short answer is that they are little glass tubes from which all the air has been evacuated, which use that air(less) gap to control the flow of electrical current. Vacuum tubes are what we used for processing and manipulating signals before we had solid-state electronics like transistors. They were in televisions, stereo amplifiers, the earliest computers, radar emitters, you name it. They were the highest of high tech for a long, long time.

And they all glow.

Electrons are lazy buggers. To get them to move from one point to another, you either have to give them so much energy they zing off into space, or you have to make it easier to move than to stay put by generating a voltage differential. Vacuum tubes do a little of both -- voltage controls the signal, but to get the current to flow across the empty interior from cathode to anode, the cathode has to be heated until the electrons jump ship. This gets them hot enough to incandesce, just like a conventional light bulb. The light isn't the point, but instead an unavoidable side effect. 

All the cozy radio programs of yesteryear -- Jack Benny, George Burns & Gracie Allen, The Lone Ranger, FDR's Fireside Chats -- were backed by a warm little glow of their own, secret and contained within the wooden cabinet of the receiver. There's something charming about that, I think.

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