[Stephen McNamera] found a schematic for a grid leak radio online and decided to throw together a few tubes on a piece of wood and see how it worked. As you can see in the video below, it works well. The video is a bit light on details, but the web page he found the plans on also has quite a bit of explanation.
The name “grid leak detector” is due to the grid leak resistor between the grid and ground, in this case, a 2.7 megaohm resistor. The first tube does everything, including AM detection. The second tube is just an audio amplifier that drives the speaker. This demodulation method relies on the cathode to control grid conduction characteristics and was found in radios up to about the 1930s. The control grid performs the usual function but also acts as a diode with the cathode, providing demodulation. In a way, this is similar to a crystal radio but with an amplified tube diode instead of a crystal.
It looks like [Stephen] wound his own coil, and the variable capacitor looks suspiciously like it may have come from an old AM radio. The of the old screw terminal tube sockets on the wood board looks great. Breadboard indeed! What we didn’t see is where the 150 V plate voltage comes from. You hope there is a transformer somewhere and some filter capacitors. Or, perhaps he has a high-voltage supply on the bench.
While tubes are technologically passe, we still like them. Especially in old radios. Just take care around the high voltages, please.
[Nick Poole] shared his circuitous journey into the obscure world of homemade vacuum tubes on the Supercon 2022 stage. It began innocently enough when he saw [Usagi Electric]’s single bit computer vacuum tube computer, which uses dozens of vacuum tubes. He got to wondering, could you make vacuum-tube-like devices containing multiple elements? There are some examples, like the 256-bit memory Selectron tube from the 1950’s, but nothing general purpose like a 555 timer or quad NAND gate packages. Unencumbered by a deep understanding of how vacuum tubes work, [Nick] proceeds to fill this void by imagining Integrated Thermionic, a fictitious company that exists in an alternate history where transistors were not invented and the vacuum tube reigns supreme. He also showcases a variety of innovative products that Integrated Thermionics manufactured over the decades, including surface mount tubes.
If you keep up with various retro vacuum tube projects, you probably have run across [UsagiElectric] aka [David]’s various PCBs that he makes on his own Bridgeport EZ-Track 3-axis milling machine — massively oversized for the job, as he puts it. In a recent video, [David] walks us through the steps of making a sample PCB, introducing the various tools and procedures of his workflow. He points out that these are the tools he uses, but the overall process should be similar no matter what tools you use.
For this video, [David] makes a half-adder circuit out of four vacuum tubes plus a seven-segment VFD tube to show the combined sum and carry outputs. Momentary switches are used to generate the two addends. Using this example, he proceeds to design, simulate, build and demonstrate a working circuit board. We like his use of the machined pin socket inserts for building a vacuum tube socket directly into the board.
Now this process isn’t for everyone. First of all, a Bridgeport mill is a pretty good sized, and heavy, tool. That said, these procedures should adapt well to other milling machines and engravers. We should point out that [David] is making boards mostly for vacuum tubes, where circuit trace width and spacing distances are generous. If you’re planning to make home PCBs for a 273-pin PGA chip, this isn’t the technique for you.
It seems that the bulk of [David]’s vacuum tube PCBs are single-sided, and reasonably so. They use wire links here and there to jump over traces. Adapting this process to double-sided PCBs is doable, but more complex. Are you milling double-sided boards in your lab? If so, let us know about it in the comments below.
There’s an unknown piece of military electronic gear being investigated over on [Usagi Electric]’s YouTube channel (see video below the break). The few markings and labels on the box aren’t terribly helpful, but along with the construction and parts, seem to identify it as relating to the US Navy from the WWII era. Its central feature is a seeing-eye tube and an adjustment knob. [David] does a bit of reverse engineering on the circuit, and is able to fire it up and get it working, magic eye squinting and all.
But there’s still the unanswered question, what was this thing supposed to do? Besides power, it only has one input signal. There are no outputs, except the “data” presented visually by the magic eye tube. Commenters have suggested it was used with sonar equipment, calibration tool, RTTY tuning aid, light exposure meter, etc. But if you dust off your copy of Navships 900,017 “Radar Systems Fundamentals” from 1944 and turn to page 249, there’s a section entitled Tuning Indicator that describes this circuit, almost.
Unless you stay up all night and have a dozen printers going, it’s probably way too late to make one of these beautiful prop weapons designed by [Andrew] of The Ray Gun Project in time for Halloween. Most of them are from Call of Duty: Zombies, though there is an awesome little disco grenade from Fortnite as well.
All of the projects are fantastic, but we chose to highlight the Wunderwaffe DG-2 from COD: Zombies because, well, vacuum tubes. For those unfamiliar with the ‘waffe’s operation, those vacuum tubes act as ammo magazines. Once they’re empty, you power them down with that big red switch and eject them one at a time with the lever, just like in the game.
Inside is a Feather M0 Express that runs the RGB LEDs and uses a Hall effect sensor to read magnets in the quick-change ammo magazine. You can see how it works in the demo video after the break.
There are BOMs for several of the prop weapons, along with assembly drawings and support forums for anyone who wants to build their own. Don’t feel like gathering all the bits and bobs yourself? [Andrew] is selling hardware packs for the ray gun, but you’ll have to scrounge the parts yourself if you want to build the Wunderwaffle.
As those of us who work in electronics are grappling with a semiconductor shortage making common devices unobtainable and less common ones very expensive, it’s worth noting that there’s another supply crunch playing out elsewhere in the electronics industry. It’s not one that should trouble most readers but it’s a vexing problem in the guitar amp business, as guitar.com reports. At its root is the Chinese Shuguang factory, which it is reported has been forced to close down and move its operations. There’s nothing about this on the Shuguang website, so we hope that the plant has been relocated successfully and production will resume.
The specialist audio market that forms the lion’s share of tube customers in 2021 is a relatively tiny corner of the electronics business, but it’s interesting to note that the three major plants which supply it, in Slovakia, Russia, and China, are still not enough to prevent it being vulnerable when one of them fails. The likelihood of a fourth tube plant emerging somewhere else in the 2020s to take up the slack is not high, but it’s evident that the demand remains healthy enough.
Vacuum tubes fueled a technological revolution. They made the amplification of signals a reality for transatlantic telephone cables (and transcontinental ones too), they performed logic for early computers, and they delivered that warm fuzzy sound for high fidelity audio. But they were labor intensive to produce, and fragile, so semiconductors came along and replaced tubes in almost every application. But of course tubes are still with us and some tube applications are still critical — you’ll find them used in high-power RF and there are even satellites that depend on klystrons. So there are still experts in tube fabrication around, and Charles Alexanian is one of them. His newly-published talk at the 2018 Hackaday Supercon (found below) is a whirlwind tour of what goes into building a vacuum tube.
The process of building your own vacuum tube isn’t hard, but it’s not a walk in the park. The difficulty comes in the sheer number of processes, and the tricks of the trade found at every step. Charles’ methaphor is that if you build one tube at a time each step is like learning to ride a bicycle again, but if you build many you get into the swing of it and things go a lot better. His talk is a brief overview of everything, but if you want to drill down he also wrote an excellent article that goes further in depth.
In the working components of each tube are the precision parts: the grid (or grids). For the tube to function well these must be accurately produced which can be done with photolithography, but Charles usually uses a winding process involving a lathe. After winding, the grid is stretched to straighten the nickel wire, then cut to length. Other components such as the plate are stamped using an arbor press and simple forms he fabricates for the purpose.
Tube sealing machine common in factories
Lathe setup used for 1-off tube sealing
Tube being tested for leaks
Two glass components are used, the dome itself, and feedthrough stems that have a wire for each lead passing through a glass disc. The components are spot welded to the inside portion of the feedthrough stem, then the glass is fused together, again using a lathe. It heads over to a pumping station to evacuate the air from the tube, and is finally tested for leaks using a handheld Tesla coil (see, we knew those weren’t just toys).
Charles proposed his Supercon appearance as a chance to fabricate tubes on-site. We loved the idea, but the amount of gear needed is somewhat prohibitive (annealing ovens, vacuum cabinets, torches for sealing, and the need for 220v, plus space for it all). That’s too bad since we were really hoping to see the Jolly Wrencher in Nixie-tube form — incidentally, Charles says Nixes are simple to make compared to amplifiers and switches. He also mentions that the majority of your time is spent “washing” parts to remove impurities. Fair enough, that part sounds boring, but we hope to endure it at some point in the future because vacuum tube fabrication demos feel very much like a Hackaday event!
