Curve Tracer Design For Power Vacuum Tubes Testing

Regardless of the mythical qualities that are all too often attributed to vacuum tubes, they are still components that can be damaged and wear out over time. Much like with transistors and kin, they come with a stack of datasheets, containing various curves detailing their properties and performance. These curves will change as a part ages, and validating these curves can help with debugging a vacuum tube-based circuit. This is where one can either spend an enormous sum on a commercial curve tracer like the Tektronix 570, or build your own, as [Basin Street Design] has done.

A semi-retired electronics design engineer by trade, he has previously covered the development of the curve tracer on Instructables for the version 1 and version 1.1. What this device essentially allows you to do is sweep the connected tube through its input parameter ranges, while observing the resulting curves on an attached (external) oscilloscope. Here a storage oscilloscope (or DSO) is immensely helpful to capture the curves.

In the project pages, the in-depth theory and functioning of the circuitry is explained, along with the schematics and a number of builds. The project has been around since before the VBA tracer which we covered last year, both of which are infinitely more affordable than a genuine Tektronix 570.

Thanks to [Fernando] for the tip.

Supercon 2022: Samy Kamkar’s Glowing Breath

Sometimes the journey itself is the destination. This one started when [Samy] was 10 and his mom bought a computer. He logged on to IRC to talk with people about the X-Files and was WinNuked. Because of that experience, modulo a life of hacking and poking and playing, the talk ends with a wearable flex-PCB Tesla coil driving essentially a neon sign made from an ampule of [Samy]’s own breath around his neck. Got that? Buckle up, it’s a rollercoaster.

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A Homemade Tube Amplifier Featuring Homemade Tubes

With the wealth of cheap and highly integrated audio amplifier modules on the market today, it takes a special dedication to roll your own from parts. Especially when those parts include vacuum tubes, and doubly so when you make the vacuum tubes from scratch too.

Now, we get it — some readers are going to find it hard to invest an hour in watching [jdflyback] make a pair of triodes to build his amplifier. But really, you’ve got to check this out. Making vacuum tubes with all the proper equipment — glassblower’s lathe, various kinds of oxy-fuel torches, all the right hand tools — is hard enough. But when your lathe is a cordless drill, and you’re using a spot welder that looks like it’s cobbled together from junk, your tube-making game gets a lot harder. Given all that, you’d expect the tubes to look a lot rougher than they are, but even with plain tungsten wire heaters and grids made from thick copper wire, they actually work pretty well. Sure, the heaters glow as bright as light bulbs, but that’s all part of the charm.

Speaking of charm, we just love the amp these tubes went into. Built in 1920s breadboard-style, the features some beautiful vintage mica capacitors and wirewound resistors, plus a variable resistor the likes of which we’ve never seen. The one nod to modernity is the clever use of doorbell transformers, one for a choke and one for the speaker transformer. They don’t sound great, but there’s no doubt they work.

We may have seen other homemade vacuum tubes before — we even recently featured a DIY X-ray tube — but there’s something about [jdflyback]’s tubes that really gets us going.

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This Scratch-Built X-Ray Tube Really Shines

On no planet is making your own X-ray tube a good idea. But that doesn’t mean we’re not going to talk about it, because it’s pretty darn cool.

And when we say making an X-ray tube, we mean it — [atominik] worked from raw materials, like glass test tubes, tungsten welding electrodes, and bits of scrap metal, to make this dangerously delightful tube. His tool setup was minimalistic as well– where we might expect to see a glassblower’s lathe like the ones used by [Dalibor Farny] to make his custom Nixie tubes, [atominik] only had a small oxy-propane hand torch to work with. The only other specialized tools, besides the obvious vacuum pump, was a homebrew spot welder, which was used to bond metal components to the tungsten wires used for the glass-to-metal seals.

Although [atominik] made several versions, the best tube is a hot cathode design, with a thoriated tungsten cathode inside a copper focusing cup. Across from that is the anode, a copper slug target with an angled face to direct the X-rays perpendicular to the long axis of the tube. He also included a titanium electrode to create a getter to scavenge oxygen and nitrogen and improve the vacuum inside the tube. All in all, it looks pretty similar to a commercial dental X-ray tube.

The demonstration in the video below is both convincing and terrifying. He doesn’t mention the voltage he’s using across the anode, but from the cracking sound we’d guess somewhere around 25- to 30 kilovolts. The tube really gets his Geiger counter clicking.

Here’s hoping [atominik] is taking the proper precautions during these experiments, and that you do too if you decide to replicate this. You’ll also probably want to check out our look at the engineering inside commercial medical X-ray tubes.

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Retrotechtacular: The Forgotten Vacuum Tube A/D Converters Of 1965

In any era, the story of electronics has very much been about figuring out how to make something happen with what’s available at the time. And as is often the case, the most interesting developments come from occasions when needs exceed what’s available. That’s when real innovation takes place, even if circumstances conspire to keep the innovation from ever taking hold in the marketplace.

This gem of a video from the Antique Wireless Association has a perfect example of this: the long-lost analog-to-digital converter vacuum tube. Like almost every mid-20th-century innovation in electronics, this one traces its roots back to the Bell Laboratories, which was keenly interested in improving bandwidth on its massive network of copper lines and microwave links. As early as 1947, one Dr. Frank Gray, a physicist at Bell Labs, had been working on a vacuum tube that could directly convert an analog signal into a digital representation. His solution was a cathode ray tube similar to the CRT in an oscilloscope. A beam of electrons would shine down the length of the tube onto a shadow mask containing holes arranged in a “reflected binary code,” which would later be known as a Gray code. The analog signal to be digitized was applied to a pair of vertical deflector plates, which moved the beam into a position along the plate corresponding to the voltage. A pair of horizontal deflector plates would then scan the beam across the shadow mask; where electrons fell on a hole, they would pass through to an output plate to be registered as a bit to be set.

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Hackaday Prize 2022: Glass Tube Solar Thermionic Converters

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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A beige 1960s radio receiver, inset with vacuum tubes

Busted 1960s Vacuum Tube Radio Sings Again

Restoring a vintage radio receiver has the potential to be a fun weekend project, but it pays to know what you’re up against. Especially in the case of vacuum tube electronics, running down gremlins in the circuits isn’t always a straightforward process (also, please mind the high voltage that is present in old vacuum tube equipment). [Mr Carlson] has a knack for getting old radios humming once again, and his repair of a 1960s General Electric barn find radio receiver is a thorough masterclass in vintage electronics servicing.

Seriously, if you’ve got a spare ninety minutes, the video (after the break) is a thorough and unabridged start-to-finish diagnosis and repair of a vintage radio, and an absolute must for anyone interested in doing the same. This barn find radio was certainly showing its age, and it wasn’t long before in-circuit testing found an open filament in one of several vacuum tubes, but the radio was still stubbornly silent. Further testing revealed that the IF transformers were out of spec, requiring servicing and alignment. After fine tuning both the IF and RF sections of the radio, things were definitely looking (and sounding) better.

Fine tuning the various components in the radio went a long way to living up to its “long range” claims, and by the end of the video, it’s almost impossible to find dead air on the AM dial of this radio. If you’ve never had to make fine adjustments to a receiver, especially of this vintage, this video has all the details you’ll need. With the board exposed, [Mr Carlson] also took care of some preventative maintenance, including replacing the original filter capacitor with newer components, as well as replacing the mains safety capacitor with an even safer modern alternative.

We can’t get enough of these restorations, so make sure to check out our detailed write-up of restoring a WWII aircraft radio.

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