Vunderful Vacuum Tubes

“History is written by the victors,” as the old saying goes. George Orwell echoed this chilling sentiment in his novel 1984, where the Party controls history: “Who controls the past controls the future: who controls the present controls the past.” (Just reading this sends shivers running up and down my spine.)

Sad to relate, in many cases these days, the victors don’t write history — it’s written by Hollywood (well, by the American film industry). For example, many Americans believe that Thomas Alva Edison invented the first electric light bulb in 1879. They believe this because they saw the 1940 movie, Edison, the Man, starring Spencer Tracy. However, this is not, in fact, the case.

To be honest, there were many contenders before Edison. For example, the British astronomer, chemist, and inventor Warren De la Rue created one of the world's first electric light bulbs by enclosing a platinum coil in a vacuum tube and passing an electric current through it in 1840, which was almost 40 years before Edison. (In this context, “vacuum tube” means a sealed glass tube from which the air has been evacuated to create a vacuum inside.)

Furthermore, the English physicist, chemist, and inventor Sir Joseph Wilson Swan successfully demonstrated a true incandescent bulb using a carbonized thread (similar to Edison's) in a vacuum tube in 1878, which was a year earlier than Edison's. From this, the cynical amongst us might say that the true key to making history isn't being first, it’s hiring a good press agent, getting a movie deal, and (preferably) being played by Spencer Tracy. Thankfully, I’m not bitter.

Sometime around 1880 to 1883, one of Edison’s assistants, William Joseph Hammer, observed that electrons could flow through the vacuum from the heated filament to a metal plate inside the bulb. This phenomenon later became known as the “Edison effect.”

Sadly, Edison did not pursue this discovery further. In fact, it wasn’t until 1904 that the English physicist John Ambrose Fleming realized the Edison effect could be used to detect radio waves and convert them into electrical signals, leading to the invention of his vacuum tube "diode."

Two years later, in 1906, the American inventor Lee de Forest introduced a third electrode, called the “grid,” into his vacuum tube. The resulting “triode” could function as both an amplifier and a switch. De Forest’s triode revolutionized the field of broadcasting, and its ability to act as a switch would go on to have a profound impact on the development of digital computing.

Now, you may be muttering, “All this is ancient history, tell me something new, Grandpa,” but it’s not as ancient as you might think. Allow me to expound, elucidate, and explicate (don’t worry, I’m a professional).

When I was around 12 years old, my parents took out subscriptions to two hobby magazines in my name: Practical Electronics and Practical Wireless. In those days, at the end of each year, subscribers could purchase a binder — at a reasonable cost — to store and preserve that year’s issues.

What I didn’t realize at that time was that it was also possible to purchase that year’s offerings in book form. I only found this out a week or so ago when my friend Joe Farr in the UK sent me a copy of the 1957 edition (the year I was born) of Practical Wireless that he'd found on eBay as a present for my 68th birthday.

The reason I mention this here is that, on the very first page, the “By the Editor” column starts as follows (note that “valve” is an alternative name for “vacuum tube” in countries influenced by British English, including the United Kingdom, Australia, New Zealand, India, and South Africa):

Readers will have noted that in recent issues we have devoted considerable space to transistors. It is natural that our readers, all of whom are practical constructors, and therefore interested in experiment, should press for more articles on this subject, and we shall continue to publish articles on transistors and their application, increasing the amount of space devoted to the subject as transistors become more readily available. At the present time manufacture is hardly equal to the demands of the industry. They are also at present more expensive. Because of the comparatively low stage gain more of them are required to provide a given output than would be necessary with an ordinary valve circuit. It would be idle of us to publish designs for which transistors are not readily available. Whilst transistorized circuits are the inevitable development and must eventually replace the valve, that time is far distant.

When looking through the rest of the book, we discover that only relatively few of the projects in 1957 employed transistors, while most featured vacuum tube-based implementations.

It’s the final sentence of the editor’s paragraph that makes me smile when he says, “Whilst transistorized circuits are the inevitable development and must eventually replace the valve, that time is far distant.” And it’s not only his use of “whilst,” but rather the “far distant” portion of his pontifications.

Only three years later, by the early 1960s, transistor prices had dropped, and magazines began including more transistor-based designs, especially for amplifiers, oscillators, and small radios. By the mid-1960s, a significant shift had occurred. Transistor projects had become commonplace in hobbyist magazines. Vacuum tubes were still used in high-voltage, radio, and audio power applications, but were no longer dominant. By 1970, transistors had largely replaced vacuum tubes in hobby electronics, and integrated circuits (ICs) had started showing up too, especially in digital logic projects.

These days, we’re so used to hearing about the latest-and-greatest in semiconductor devices and technologies that we tend to forget vacuum tubes are still in use for certain applications. These include audio equipment (especially high-end and guitar amplifiers); high-power radio frequency (RF) transmitters; scientific, medical, and industrial equipment; military and some space applications (tubes are more resistant to electromagnetic pulses, or EMPs, than semiconductors); and some specialized research applications.

It’s worth noting that if you can lay your hands on some old, non-functional vacuum tubes, you can use them to create tasty-looking projects, such as my own “Antique Audio Artifact” shown below.

In this case, I chopped the leads off a bunch of defunct tubes and mounted them on a thin sheet of wood with holes in the appropriate places. This wood, which was painted black, was then mounted in a small faux-antique suitcase. I attached tricolor light-emitting diodes (LEDs) to the bottom of each tube. A small microphone mounted on the front of the case feeds the input to a cheap-and-cheerful 8-pin MSGEQ7 seven-band graphic equalizer chip (see the data sheet). In turn, this chip feeds an Arduino Uno, which controls the LEDs in response to the audio input.

Anyone can flash a bunch of LEDs, but vacuum tubes really add some steampunk visual appeal. This audio artifact is sitting on the desk as we speak, happily responding to any ambient sounds.

So, what do you think about all this? As always, I welcome your captivating comments, querulous questions, and sagacious suggestions, all of which you can present on Hackster.io's "Throwback Thursdays" Discord channel. I look forward to seeing you there.

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