Flipped Transformer Powers Budget-Friendly Vacuum Tube Amp

November 7, 2023 by Dan Maloney 31 Comments

If you’ve ever wondered why something like a radio or a TV could command a hefty fraction of a family’s yearly income back in the day, a likely culprit is the collection of power transformers needed to run all those hungry, hungry tubes. Now fast-forward a half-century or more, and affordable, good-quality power transformers are still a problem, and often where modern retro projects go to die. Luckily, [Terry] at D-Lab Electronics has a few suggestions on budget-friendly transformers, and even shows off a nice three-tube audio amp using them.

The reason transformers were and still are expensive has a lot to do with materials. To build a transformer with enough oomph to run everything takes a lot of iron and copper, the latter of which is notoriously expensive these days. There’s also the problem of market demand; with most modern electronics favoring switched-mode power supplies, there’s just not a huge market for these big lunkers anymore, making for a supply and demand equation that’s not in the hobbyist’s favor.

Rather than shelling out $70 or more for something like a Hammond 269EX, [Terry]’s suggestion is to modify an isolation transformer, specifically the Triad N-68X. The transformer has a primary designed for either 120 or 230 volts, and a secondary that delivers 115 volts. Turn that around, though, and you can get 230 volts out from the typical North American mains supply — good enough for the plate supply on the little amp shown. That leaves the problem of powering the heaters for the tubes, which is usually the job of a second 6- or 12-volt winding on a power transformer. Luckily, the surplus market has a lot of little 6.3-volt transformers available on the cheap, so that shouldn’t be a problem.

We have to say that the amp [Terry] put these transformers to work in sounds pretty amazing — not a hint of hum. Good work, we say, but we hope he has a plan in case the vacuum tube shortage gets any worse.

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Nixie Tube RPN Calculator Project

November 7, 2023 by Chris Lott 12 Comments

If you like Nixie tubes and/or DIY calculators, checkout this interesting talk from the HP Handheld Conference in Orlando last month by [Eric Smith] from Brouhaha and [John Doran] from Time Fracture. For 20-some years, [Eric] and the late [Richard Ottosen] have been incrementally developing various DIY calculators — this paper from the 2005 HHC conference is an excellent overview of the early project. [John] got one of those early DIY calculators and set about modifying it to use Nixie tubes. However, he got distracted by other things and set it aside — until reviving it earlier this year and enlisting [Eric]’s aid.

This presentation goes over the hardware aspects of the design. Unlike the earlier PIC-based DIY calculators, they decided to use a WCH RISC-V processor this time around. The calculator’s architecture is intentionally modular, with the display and keyboard housed in completely separate enclosures communicating by a serial interface. If the bulkiness alone doesn’t exclude it from being pocket-sized, the 170 VDC power supply and 1/2 W per digit power consumption certainly does. This modularity does lend itself to DIYers replacing the display, or the keyboard, with something different. [Eric] wants to build a mechanical flip-digit display for his unit. As for the software, [Eric] reviews the firmware approach and some future upgrades, such as making it programmable and emulating other flavors of HP calculators.

If you’re embarking on a similar project yourself, check out this talk and take notes — there are a lot of interesting tidbits on using Nixie tubes in the 21st century. If [Eric]’s name sounds familiar, you may know him from the Nonpareil calculator software used on many emulators and DIY calculator projects, one of which we covered some years ago. [John] is also a long-time tinkerer, and we wrote about his gorgeous D16/M HCMOS computer system back in 2012. Thanks to [Stephen Walters] for sending in the tip.

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Wooden Game Boy Is A Challenging Intro CNC Project

November 4, 2023 by Dan Maloney 12 Comments

[Sebastian] describes himself as “a total noob” when it comes to CNC, so in an attempt to get to know his new CNC router, he chose about the most complex possible project — replicating an original Game Boy case in wood. And spoiler alert: he nailed it.

Of course, he did have a few things going for him. At least from a straight woodworking perspective, it’s hard to go wrong by choosing walnut as your material. Then again, it can be unforgiving at times, and picky about tooling, which is probably why [Sebastian] used nine different tools to get the job done. But where he upped the difficulty level was in reproducing so many of the details of the original injection-molded plastic case. There are top and bottom shells, each of which has to be milled from both sides. This makes registration tricky when the parts are flipped. Specific indexing holes were used for that, along with the old “blue tape and CA glue” fixturing trick, which seemed to work quite well. For our money, though, the best bit is the lettering on the front face, which was milled out with an engraving bit and then filled with a spritz of white spray paint. A surfacing bit then came along to knock the overspray down, leaving labels that contrast beautifully with the dark wood. Gorgeous!

It wasn’t all easy sailing, though. There are just some things plastic can do that wood can’t, like holding screw threads in small studs without splitting. So, the case had to be glued shut once the mix of salvaged and new components went in. Still, it looks fabulous, and [Sebastian] says what we see in the video below is the one and only piece. Pretty sweet for the first try. Surprisingly, it doesn’t seem as if we’ve seen a wooden Game Boy before — a wooden NES, sure, but not a Game Boy.

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Machine Teaches Morse Code

November 3, 2023 by Al Williams 4 Comments

If you are a ham radio operator of a certain age, you probably remember ads for “The Instructograph,” a mechanical device for learning Morse code. [Our Own Devices] has an ancient specimen of the machine and shows us how it works in the video below. The machine is a model of simplicity. You wind up a spring-driven motor like you would for an old record player or music box. A slider sets the playback rate, and paper tape starts to spin.

The paper tape looks like computer tape, but since it only has literal long and short notches, it has two distinct sides. When you learned one set of messages, you could flip the tape over and get more practice that way. How did the machine read the paper tape? With a mechanical contact. Literally, if the paper had a hole in it, you made the circuit. If it didn’t, the circuit was broken. A buzzer and batteries or some other kind of sounder was all you needed.

The company was in business for 50 years. The newer versions had more electronics, but they always used the paper tape mechanism to store the code practice sessions. A 1962 ad noted that the machine could play back the tapes from three words a minute up to 40. You could buy or rent the machine, and we always assumed it was pretty pricey for its day. Around 1965, a new unit would cost $53 but did not include a headset or a key. So that was actually more reasonable than we expected. In 1965, a brand-name clock radio cost about $50, so it wasn’t any more than that.

Everyone has their own favorite method for learning code, especially [Ludwig Koch]. At least you don’t have to learn Alex-style.

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Partial Relay-Based Calculator Puts The Click Where It Counts

November 3, 2023 by Dan Maloney 15 Comments

It looks like [Michal Zalewski] is raising the next generation the right way. First, his eldest son asks for help building a one-bit computer from discrete transistors. Not to be left behind, his little brother then asked for help with an even more retro project, which resulted in this partially relay-based calculator. Maybe there is some hope for the future.

Now, purists will no doubt notice the ATmega64 microcontroller sitting in the middle of the main PCB on this project and cry “Foul!” But perfect is the enemy of done, and as [Michal] explains, at $6 a pop for the Omron relays he and his son chose, there’s only so far you can go with relay logic before you’re taking out a second mortgage. So the relays are limited to the ALU of the calculator, along with the drivers for the six seven-segment LED displays. The microcontroller is just there for housekeeping functions like scanning the keyboard and decoding digits. All the actual calculations are in the relay logic, not silicon. And we’d be remiss not to praise his son’s stylistic choices for this design — that it uses relays with clear covers, and that it has ~~single-sided~~ PCBs with curvy, ~~hand-drawn traces~~ traces that look hand-drawn on old-school yellow substrate. [Michal]’s heart must swell with pride to have fathered someone with such exquisite taste.

For his part, [Mikal] did some really good documentation for this build, including excellent descriptions of Boolean math with half- and full-adders and how relays are used to create the basic logic gates that comprise them. The calculator itself is still a work in progress, with microcontroller code still in development, but it’s working enough that you can enjoy the display driver’s clickiness in the video below. If that doesn’t do it for you, we’ve got other relay calculators to scratch that click itch. Continue reading “Partial Relay-Based Calculator Puts The Click Where It Counts” →

Random Number Generator Is A Blast From The Past

November 2, 2023 by Tom Nardi 16 Comments

Hackers love random numbers, or more accurately, the pursuit of them. It turns out that computers are so good at following our exacting instructions that they are largely incapable of doing anything that would fit the strict definition of randomness — which has lead to some elaborate methods of generating the unexpected.

Admittedly, the SB42 Random Number Generator built by [Simon Boak] isn’t exactly something you’d be using for cryptography. The method used to generate the digits, a pair of 555 timers sending pulses through linear-feedback shift registers, would at best be considered pseudo-random. Plus the only way of getting the digits out of the machine is by extracting them from the Nixie tubes with your Mark I Eyeballs. But it absolutely excels at the secondary reason many hackers like to build their own randomness rigs — it looks awesome.

Externally, it absolutely nails the look of a piece of vintage DIY year. Down to the classic white-on-black label tape. But open up the hood, and you’re treated to a real rarity these days: wirewrap construction. In an era where you can get PCBs made and shipped to your door for literally pennies, [Simon] is out there keeping the old ways alive. It doesn’t just look the part either. Unlike most modern projects we see, there isn’t a multi-core microcontroller behind the scenes doing all the work, it’s logic gates all the way down.

This isn’t the first random-ish number generator that we’ve seen use shift registers. But if you’re looking for something that might actually pass some randomness checks, and don’t mind working with something a bit spicy, you could check out some of the previous devices we’ve covered that used radioactive decay as an entropy source.

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Make Your Own 1970s Magnetic Stripe Cards

October 25, 2023 by Jenny List 8 Comments

We’re now all used to near-limitless storage on flash and other semiconductor technologies, but there was a time when persistent storage was considerably less easy to achieve. A 1970s programmable calculator from Sharp approached the problem with magnetic strips on special cards, and since [Menadue] has one with no cards, he set about making his own.

These cards are a little different to the credit-card-style cards we might expect, instead they’re a narrow strip with a magnetic stripe down their centre. The unusual feature can be found at the edge, where a row of perforations provide the equivalent of a clock line.

The newly manufactured cards have the clock slots machined along their edges, and then the magnetic part formed from self-adhesive magnetic strip. This last thing is a product we were not aware existed, and can think of plenty of possible applications.

The result as you can see in the video below the break are some cards with variable reliability. There’s a suggestion that white cards might work less well with the infrared light used in the clock detector, also a suspicion the low batteries make reading less easy, but still he’s able to retrieve a stored program. An extinct medium is revived.

Longtime readers will know we’ve spent time in calculator country before.

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