tube

109 Articles

Reactive Load For Amplifiers Teaches Lessons About Inductors

August 24, 2022 by 26 Comments

The sound produced by any given electric guitar is shaped not just by the instrument itself but by the amplifiers chosen to make that sound audible. Plenty of musicians swear by the warm sound of amplifiers with vacuum tube circuits, but they do have some limitations. [Collin] wanted to build a reactive load for using tube amps without generating a huge quantity of sound, and it resulted in an interesting project that also taught him a lot about inductors.

The reactive load is essentially a dummy load for the amplifier that replaces a speaker with something that won’t produce sound. Passive loads typically use resistor banks but since this one is active, it needs a very large inductor to handle the amount of current being produced by the amplifier. [Colin] has also built a headphone output into this load which allows it to output a much smaller quantity of sound to a headset while retaining the sound and feel of the amplifier tubes, and it additionally includes a widely-used tone control circuit as well.

There’s a lot going on in the design of the circuitry for this amplifier load, including a lot of research into low-frequency inductors that can handle a significant amount of current. [Collin] eventually ended up winding his own, but the path he took to it was long and winding. There’s a lot of other circuit theory discussed as well especially with regards to the Baxandall EQ that he built into it as well. And, if you’d like to learn more about tube amplifiers in general, take a look at this piece which notes one of the best stereo amps ever produced.

Hackaday Prize 2022: Glass Tube Solar Thermionic Converters

April 27, 2022 by 13 Comments

Typically, if you want to convert solar energy into electrical energy, you use either photovoltaic (PV) cells, or you use the sunlight to create steam to turn a turbine. Both of these methods are well-established and used regularly in both small- and grid-scale applications. However, [Nick Poole] wanted to investigate an alternative method, using thermionic converters for solar power generation.

[Nick] has been gearing up to produce various styles of vacuum tubes, and noted that the thermionic effect that makes them work could also be used to generate electricity. They are highly inefficient and produce far less power than a photovoltaic solar cell, meaning they’re not in common use. However, as [Nick] notes, unlike PV cells etched in silicon, a thermionic converter can be built with basic glassworking tools, requiring little more than a torch, a vacuum pump, and a spot welder.

Experiments with a large lens to focus sunlight onto a 6V3A diode tube showed promise. [Nick] was able to generate half a volt, albeit at a tiny current, with the design not being optimized for thermionic conversion. Further experiments involved electrically heating a pair of diode tubes, which was able to just barely light an LED at 1.7 V and a current of 7.5 uA. The conversion efficiency was a lowly 0.00012%, around 5 orders of magnitude worse than a typical PV cell.

[Nick]’s hope is that he can produce a tube designed specifically to maximize thermionic conversion for energy generation purposes. It’s likely there is some low-hanging fruit in terms of gains to be made simply by optimizing the design for this purpose, even if the technique can’t compete with other solar generation methods.

In any case, we’re eager to see what [Nick] comes up with! We love to see makers building tubes in their own home workshops.

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This Ham Radio Is Unsafe At Any Frequency

December 3, 2021 by 40 Comments

When we were kids we rode bicycles without pads and helmets. We drank sugary drinks. We played with chemistry sets and power tools. We also built things that directly used AC line current. [Mike] remembers and built one, presumably more to discuss the safety precautions around things that can shock you and not entice you to duplicate it. He calls it The Retro QRP Widowmaker, if that’s any kind of a hint. (Video of this unsafe transmitter also embedded below.)

The design showed up from time to time in old electronic magazines. Built on an open board and with no ground wire, the radio didn’t need a complex power supply. This wasn’t limited to transmitters, either. Some TVs and radios had a “hot chassis.” That’s why we were taught to touch an unknown chassis with the back of your hand first. A shock will contract your muscles and that will pull your arm away instead of making you grab the electrically active part.

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Modern Tube Tester Uses Arduino

September 24, 2021 by 13 Comments

There was a time when people like us might own a tube tester and even if you didn’t, you probably knew which drug store had a tube testing machine you could use for free. We aren’t sure that’s a testament to capitalistic ingenuity or an inditement of tube reliability — maybe both. As [Usagi] has been working on some tube-based projects, he decided he needed a tester so he built one. You can see the results in the video, below.

The tester only uses 24V, but for the projects he’s building, that’s close to the operation in the real circuits. He does have a traditional tube tester, but it uses 100s of volts which is a different operating regime.

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You Can Put Toothpaste In The Tube (With Effort)

July 5, 2021 by 20 Comments

Old wives’ tales, folk knowledge, common sayings, and even cliches and idioms are often taken as givens since they form an often unnoticed part of our vocabulary and culture. There’s so many examples that it’s possible to fill a 17-season TV show busting potential myths like these, and even then there are some that slipped by. For example, the saying “you can’t put toothpaste back in the tube” which, as it turns out, is not as impossible as we might be led to believe.

This video is the product of [Tyler Bell] who has taken this idiom on as a challenge. To figure out if it was possible he first got to work building a vacuum chamber, which turned out to be a little easier than he thought it would be. After cutting a piece of polycarbonate tube and sanding it down, all that was needed were some rubber gaskets and fittings for the vacuum pump.

From there, the theory was to put an empty toothpaste tube into the vacuum chamber, pump all of the air out, and let atmospheric pressure “push” the toothpaste back into the tube. During [Tyler]’s first run he thought that it had worked successfully but it turned out that he had just inflated the empty toothpaste tube like a balloon. Further iterations were able to return some of the toothpaste to the tube, but each time some air would eventually work its way into the toothpaste which would immediately fill the remaining space in the tube with air rather than toothpaste.

While not completely successful, he was able to get some toothpaste back into the tube with a relatively small bill of materials. It’s not likely that this experiment will result in a change of this particular idiomatic expression, but it was interesting to put it to the test nonetheless. For other instances of toothpaste and its relationship to tubes, both inside and out, be sure to check out this recent piece on various methods of toothpaste storage.

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Vacuum Tube Magic Comes To The 741

June 19, 2021 by 41 Comments

Some of you may remember a recent project that featured on these pages, a 555 timer reproduced using vacuum tubes. Its creator [Usagi Electric] was left at loose ends while waiting for a fresh PCB revision of the 555 to be delivered, so set about creating a new vacuum tube model of a popular chip, this time the ubiquitous 741 op-amp. (Video, embedded below.)

The circuit is fairly straightforward, using six small pentodes. The first two are  a long-tailed pair as might be expected, followed by two gain stages, then a final gain stage feeding a cathode follower with feedback. It’s neatly built on a PCB with IC-style “pins” made from more PCB material, then put in a huge replication of an IC socket on a wooden baseboard.

The result is an op-amp, but not necessarily a good one. He looks at the AC performance instead of the DC even though it’s a fully DC-coupled circuit, and finds that while it performs as expected in a classic op-amp circuit it still differs from the ideal at higher gain. The frequency response is poor too, something he rectifies by replacing the feedback capacitor with a smaller value. Sadly he doesn’t look at its common mode performance, though we’d expect that without close matching of the tubes it might leave something to be desired.

It’s obvious that this project would never be selected as an op-amp given the quality of even the cheapest silicon op-amp in comparison. But its value is in a novelty, a talking point, and maybe a chance to learn about op-amps. For that, we like it.

We covered the vacuum tube 555 when details of it emerged, but if op-amps are your bag we’ve looked at a simple one very closely indeed.

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Your 1958 Punch Card Machine Tested Tubes

June 15, 2021 by 12 Comments

We think of punched cards as old-fashioned, but still squarely part of the computer age. Turns out, cards were in use way before they got conscripted by computers. Jacquard looms are one famous example. The U.S. Census famously used punched cards for tabulating the census without anything we’d consider a computer. But in the 1950s, you might have had a punched card machine on your electronics workbench. The Hickok Cardmatic was a tube tester with a difference.

About Tube Testers

While you, as a Hackaday reader, might tear into a busted TV at your house and try to fix it, most people today will either scrap a bad set or pay someone to fix it. That’s fine today. TVs are cheap and rarely break, anyway. But this hasn’t always been the case.

In the “good old days” your expensive TV broke down all the time. Most of the parts were reliable, but the tubes would wear out. If you were the kind of person who would change your own oil, you’d probably look to see if you could spot a burned out tube and try replacing it. If you couldn’t spot it, you’d pull all the tubes out. If you were lucky, there was a diagram glued inside the cover that showed where they all went back. Then you took them to the drugstore.

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