A beige 1960s radio receiver, inset with vacuum tubes

Busted 1960s Vacuum Tube Radio Sings Again

April 2, 2022 by Chris Wilkinson 12 Comments

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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Retro And New Tech Combine In This Hybrid Ham Transmitter

February 27, 2022 by Dan Maloney 9 Comments

We’ve said it before and we’ll say it again: the best part about holding an amateur radio license is that it lets you build and use your own transmitting equipment. Hams have been doing this for more than a century — indeed, it was once the only way to get on the air — using whatever technology was available. But the mix of technologies in this low-power transmitter for the 80-meter band is something you don’t see every day.

As ham [Helge Fykse (LA6NCA)] describes in the video below, the project began when he came into possession of a bonanza of vacuum tubes — 12A6 tetrodes, specifically. The new-old-stock tubes were perfect for an RF power amplifier, but that left the problem of what to use for an oscillator. [Helge] chose to meld the old with the new and used oscillator board that he designed. The board has an ATmega88 microcontroller and an Si5351 oscillator, along with a 3V3 regulator to let the module run on 12 volts. And for a nice retro touch, [Helge] put the board in a 3D printed case that looks like an old-fashioned quartz crystal.

There are some other nice design touches here too. A low-pass filter cleans up the harmonics of the oscillator’s 3.5-MHz square wave output before feeding it to the amplifier, in a nod to proper spectrum hygiene. The primary for the amp’s air-core output transformer is hand-wound, with 3D printed spacers to keep the winding neat and even. The tuning process shown below is interesting, and the transmitter was used to make a solid contact with another ham about 100 km away. And we really liked the look of [Helge]’s shack, stuffed as it is with gear both old and new.

We’ve personally tried the Si5351 for QRP transmitters before, but this blend of the old and new really makes us want to find some tubes and get to playing.

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The Eerie Sounds Of Ioalieia: An ESP32/Valve/Analog Hybrid Circuit Sculpture

January 15, 2022 by Dave Rowntree 18 Comments

We’ve not had a circuit sculpture piece for a while, so here’s “ioalieia” a lovely hybrid digital-analog sound sculpture by [Eirik Brandal] to dig into.

The host of the show is the ESP32 module, which generates audio frequency square waves, which are fed into a MCP4251 digital potentiometer. From there, it is fed into a AS3320 Voltage controlled filter (VCF), from Latvia-based ALFA (which is new to us, despite them being manufacturing electronics for sixty years!) This is an interesting device that has a four independently configurable filter elements with voltage controlled inputs for frequency control and resonance. The output from the VCF is then fed into a 6n2p (Soviet equivalent to the 12ax7) twin-triode vacuum tube, which is specifically aimed at audio applications.

The suitably distorted filtered square waves then pass into a Princeton Tech Corp PT2399 echo processor chip, which being digitally constructed, uses the expected ADC/RAM/DAC signal chain to implement an audio echo effect. As with the VCF, the echo depth can be modulated via the digipot, under the ESP32’s command. For a bit of added bling, the vacuum tube output feeds back into the ESP32, to be consumed by the internal ADC and turned into a light show via some PWM controlled LEDs. Lovely.

The final audio output from the echo chip is then fed into a speaker via a pair of LM380 amplifiers giving a power of about 5 W. It sounds pretty good if you ask us, and software configurable via Wi-Fi, giving this sculpture plenty of tweakabilty.

Of course circuit sculpture come in all shapes and sizes, and it wouldn’t do to not mention at least one sculpture clock project, and while we’re on it, here’s last year’s Remoticon circuit sculpture workshop.

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The Atari Punk Console, Now With More Vacuum Tubes

January 11, 2022 by Dan Maloney 7 Comments

Most of us have beheld the sonic glory of an Atari Punk Console, that lo-fi synth whose classic incarnation is a pair of 555 timers set up to warble and bleep in interesting ways. Very few of us, however, have likely seen an APC built from 555s that are made from vacuum tubes.

It’s little surprise to regular readers that this one comes to us by way of [David] at Usagi Electric, who hasn’t met a circuit that couldn’t be improved by realizing it in vacuum tubes. His “hollow-state” Atari Punk Console began with the 18-tube version of the 555 that he built just for fun a while back, which proved popular enough that he’s working on a kit version, the prototype of which served as the second timer for the synth. With 32 tubes aglow amid a rats-nest of jumpers, the console managed to make the requisites sounds, but lacked a certain elegance. [David] then vastly simplified the design, reducing the BOM to just four dual-triode tubes. Housed on a CNC milled PCB in a custom wood box, the synth does a respectable job and looks good doing it. The video below shows both versions in action, as well as detailing their construction.

As cool as a vacuum tube synth may be, we realize that not everyone goes for the hot glass approach. No worries — plenty of silicon Atari Punk Consoles to choose from here. There’s one built into a joystick, a circuit sculpture version complete with mini-CRT, or even eight APCs teamed up with MIDI control.

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Modern Tube Tester Uses Arduino

September 24, 2021 by Al Williams 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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a very slapdash x-ray machine on a table

Building An X-Ray Machine

September 9, 2021 by Matthew Carlson 56 Comments

While we typically encourage hackers to make their own tools or machines when practical, x-ray machines don’t usually make that list. Despite the risk of radiation, [William Osman] has done just that and built a homemade x-ray machine. After receiving an eye-watering medical bill, [William] resolves to make his own x-ray machine in the hopes of avoiding future bills. Thanks to his insurance, the total owed was smaller but still ridiculous to those who live in single-payer health care countries, but it got William thinking. What if he could make an x-ray machine to do cheap x-rays?

Armed with a cheap high voltage DC power supply he acquired from an online auction house, he started to power up his x-ray vacuum tube. A smaller power supply energizes the cathode and forms an electron beam. Then the high voltage (30-150kv) is applied as a tube voltage, accelerating the electrons into x-rays. Safety measures are taken somewhat haphazardly with Geiger counters and lead sheets. With a finger bone cast in ballistic shell [William] made his first x-ray with a long exposure on a DSLR. The next items to go in the x-ray “chamber” were a phone and a hand. The results were actually pretty decent and you can clearly see the bones.

We’ve seen homemade X-Ray machines here at Hackaday before, but not one that is constructed perhaps so haphazardly — his approach makes this obvious: don’t try this at home. Video after the break.

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Overdriving Vacuum Tubes And Releasing The Magic Light Within

July 15, 2021 by Dan Maloney 53 Comments

We’ve all seen electronic components that have been coaxed into releasing their small amount of Magic Smoke, which of course is what makes the thing work in the first place. But back in the old times, parts were made of glass and metal and were much tougher — you could do almost anything to them and they wouldn’t release the Magic Smoke. It was very boring.

Unless you knew the secret of “red plating”, of course, which [David Lovett] explores in the video below. We’ve been following [David]’s work with vacuum tubes, the aforementioned essentially smokeless components that he’s putting to use to build a simple one-bit microprocessor. His circuits tend to drive tubes rather gently, but in a fun twist, he let his destructive side out for a bit and really pushed a few tubes to see what happens. And what happens is pretty dramatic — when enough electrons stream from the cathode to the anode, their collective kinetic energy heats the plate up to a cherry-red, hence the term “red plating”.

[David] selected a number of victims for his torture chamber, not all of which cooperated despite the roughly 195 volts applied to the plate. Some of the tubes, though, cooperated in spades, quickly taking on a very unhealthy glow. One tube, a 6BZ7 dual triode, really put on a show, with something getting so hot inside the tube as to warp and short together, leading to some impressive pyrotechnics. Think of it as releasing the Magic Light instead of the Magic Smoke.

Having seen how X-ray tubes work, we can’t help but wonder if [David] was getting a little bit more than he bargained for when he made this snuff film. Probably not — the energies involved with medical X-ray tubes are much higher than this — but still, it might be interesting to see what kinds of unintended emissions red-plating generates.

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