What do you do when you find a 5 kW transmitting tube in your local electronics store? If you are [TannerTech], you build a vacuum tube tesla coil. This isn’t the usual little wimpy coil, but a big bad boy that would look at home in an old horror movie.
The first power up was a bit anticlimactic, although it was working, it wasn’t very spectacular other than the tube glowing brightly. A few adjustments and some mineral oil did the trick.
When it comes to vintage displays, everyone gravitates to Nixies. These tubes look great, but you’re dealing with a certain aesthetic with these vintage numeric tubes. There is another option. For his Hackaday Prize entry, [castvee8] is making seven-segment displays out of vintage neon lamps. It looks great, and it’s the basis of an all-vacuum tube calculator.
The core of this build are a few tiny NE-2 neon bulbs. These are the same type of bulbs you’ll find in old indicators, and require somewhere around 100 volts to fire. These bulbs are then installed in a 3D-printed frame, giving [castvee] a real seven-segment display, a plus or minus sign, and an equals sign. It’s the beginnings of a calculator, right there.
One of the recent updates to this project is controlling these displays with modern logic. That might be a bit of a misnomer, because [castvee] is using diode steering and a TTL chip to cycle through the numbers 1 to 4. The actual code to do this is running on a microcontroller, though, so that might get a pass. This is just a test, though, and the real project looks to be an all-vacuum calculator. The project is still in its early stages, but there are still months to go in the Hackaday Prize, and we can’t wait to see what comes out of this project.
As some of my previous work here at Hackaday will attest to, I’m a big fan of World War II technology. Something about going in with wooden airplanes and leaving with jet fighters and space capable rockets has always captivated me. So when one of my lovingly crafted eBay alerts was triggered by something claiming to be a “Navy WWII Range Computer”, it’s safe to say I was interested.
Not to say I had any idea of what the thing was, mind you. I only knew it looked old and I had to have it. While I eagerly awaited the device to arrive at my doorstep, I tried to do some research on it and came up pretty much empty-handed. As you might imagine, a lot of the technical information for hardware that was developed in the 1940’s hasn’t quite made it to the Internet. Somebody was selling a technical manual that potentially would have covered the function of this device for $100 on another site, but I thought that might be a bit excessive. Besides, where’s the fun in that?
I decided to try to decipher what this device does by a careful examination of the hardware, consultation of what little technical data I could pull up on its individual components, and some modern gear. In the end I think I have a good idea of how it works, but I’d certainly love to hear if there’s anyone out there who might have actually worked with hardware like this and could fill in any blanks.
We’ve seen a fair amount of Tesla coil builds, but ones using vacuum tubes are few and far between. Maybe it’s the lack of availability of high power tubes, or a lack of experience working with them among the younger crop of hackers. [Radu Motisan] built a vacuum tube Tesla coil several years back, and only just managed to tip us off recently. Considering it was his first rodeo with vacuum tubes, he seems to have done pretty well — not only did he get good results, he also managed to learn a lot in the process.
His design is based around a GI-30 medium power dual tetrode. The circuit is a classical Armstrong oscillator with very few parts and ought to be easy to build if you can lay your hands on the tricky parts. The high voltage capacitors may need some scrounging. And of course, one needs to hand-wind the three coils that make up the output transformer.
Getting the turns ratios of the coils right is quite critical in obtaining proper power transfer to the output. This required a fair amount of trial error before [Radu] could get it right.
The use of a 20W fluorescent tubelight ballast to limit the inrush current is a pretty nice idea to prevent nuisance tripping of the breakers. If you’d like to try making one of your own, head over to his blog post where you will find pictures documenting his build in detail. If you do decide to make one, be extremely careful — this circuit has lethal high voltages in addition to the obvious ones, since it operates directly from 220 V utility supply.
Vacuum tubes have been around for ages, and for better or worse, they have their advocates for use in amplifiers and preamps. However, tubes are simply inconvenient devices. Even a 12AX7 preamp tube is huge relative to a handful of transistors, tubes require weird voltages, and each and every one of them is a through-hole device that doesn’t lend itself to machine assembly.
This changed recently with the introduction a strange new tube from Japan. Noritake and Korg recently introduced a triode that uses the same packaging as VFD displays. The Korg Nutube is a vacuum tube that operates at lower voltages, is smaller than the usual preamp tubes, and still has the vacuum tube sound.
For his Hackaday Prize entry, [Kodera] is building a headphone amp with this new tube. Is a tube-based headphone amp particularly novel? No. But this is the first we’ve seen anyone playing around with this new, interesting piece of technology.
The requirements for this Nutube are simple enough, and the minimum anode voltage of this tube is just 8 V. [Kodera]’s circuit is running the tube at 12 V, and the only other circuitry in this preamp are a few coupling caps and an op-amp just before the power stage.
[Kodera] has crammed this circuit into a proper amplifier using a 2 x 15 W class-D chip from TI. It’s really a phenomenally simple circuit that’s also remarkably tiny. These kits are actually available on Tindie. Time will tell if the Nutube is picked up by some big-time manufacturers, but we’re happy to see someone is playing around with the latest advances in tube amp technology.
If we cast our minds back to the early years of the transistor, the year that is always quoted is 1947, during which a Bell Labs team developed the first practical germanium point-contact transistor. They would go on to be granted the Nobel Prize for their work in 1956, but the universal adoption of their invention was not an instantaneous process. Instead there would be a gradual change from vacuum to solid state that would span the 1950s and the 1960s, and even in the 1970s you might still have found mainstream devices on sale containing vacuum tubes.
To speed up this process, Bell Labs made every effort to publicize their invention. Thus we come to our subject today, their 1953 publicity film The Transistor, in which the electronics industry of the era is described and how each part of it might revolutionize by the transistor is laid out.
We start with a look at a selection of electronic components, among which are a few transistors. The point contact device is already described as superceded by the junction transistor, but as well as those two we are shown a phototransistor and a junction tetrode, a now-obsolete design that had two base connections.
Unexpectedly we don’t dive straight into the world of transistors, but take a look back at the earlier years of the century to the development of vacuum electronics. We’re taken through the early development and operation of vacuum tubes, then their use in long-distance radio communications, through the advent of electronics in mass entertainment, and finally into the world of radar and microwave links. Only then do we return to the transistor, with a posed shot of [John Bardeen], [William Shockley], and [Walter Brattain] hard at work in a lab. The merits of the transistor as opposed to the tube are then set out, though we can’t help wondering whether they have confused a milliwatt and a microwatt when they describe the transistor as requiring only a millionth of a watt to operate.
[Michael Wiebusch] found the leftovers of a wrecked vintage tube radio in a pile of electronics junk. Unfortunately, he could not recover any vacuum tubes in it. And to his dismay, it didn’t even have the output transformer, which he figured would have been useful in a guitar amplifier project. The output transformer is not easy to come by nowadays, so he was hoping to at least score that item for his future build. All he could dig out from his dumpster find was a pair of speakers and he ended up building nice Output-Transformer-Less Tube Guitar Amplifier around them.
Valve output stages are generally high-impedance which means they cannot be directly interfaced to low impedance speakers. An impedance matching output transformer is thus used to interface the two. Back in the day when valves were still the mainstay of audio electronics, many cheap amplifier designs would skimp on the output transformer to save cost, and instead use high impedance speakers connected directly to the amplifier output.
[Michael] found a nice reference design of an OTL amplifier for a 620 ohm single speaker. He decided to use the same design but because these speakers were about 300 ohm each, he would have to wire his two speakers in series. At this point, he decided to make his build useful as a proper guitar amplifier by adding a preamplifier stage replicated from another design that he came across. A regular halogen lamp 12V transformer takes care of the heater power supply for all the tubes, and a second, smaller 12V transformer is wired backwards to provide the 300V needed for the plate supply.
The final result is pretty satisfactory, considering that it all started with just a pair of junked speakers. Check out the result in the video after the break.