Vacuum Tube Repair After a Spectacular Failure

[Eric] has an Atwater Kent 55C AM radio from the early 1900’s. He’s been trying to restore the radio to proper working condition. His most recent pain has been with the rectifier tube. The tube is supposed to have a complete vacuum inside, but that’s not the case here. When the tube is powered up, it glows a beautiful violet color. It may look pretty, but that’s indicative that gas has leaked into the tube. It needed to be replaced.

[Eric] had a tube that would serve as a good replacement, but it’s plug didn’t fit the socket properly. He was going to have to use this old broken tube to make an adapter. Rather than just tearing the old tube apart, he decided to have some fun with it first. He hooked it up to a variac, an ammeter, and a volt meter. Then he slowly increased the voltage to see what would happen. The result was visually stunning.

The tube starts out with the same violet/blue glowing [Eric] experienced previously. As the voltage increases, it gets more and more intense. Eventually we start to see some green colors mixing in with the violets. [Eric’s] reaction to this unexpected result is priceless. As the tube gets increasingly hot, the anode starts glowing an orange-red color. Finally, the filament starts to crackle like a sparkler before the tube just gives up and completely fails.

After the light show, [Eric] moves on to replacing the tube. He begins by tapping on the old tube’s socket with the end of a screwdriver. After much tapping, the glass starts to come lose from the socket. After a bit of wiggling and twisting the tube finally came free from the socket. [Eric] luckily had an unused octal socket that fit perfectly inside of the old socket. All he needed to do to build his adapter was to connect the four pins from the old adapter to the proper pins on the octal socket. Piece of cake.

…Or so [Eric] thought. After testing some new tubes with a tube tester, he realized he had soldered all four pins incorrectly. On top of that, he had super glued the adapter together. He eventually got the two pieces apart. This time he removed all of the unused pins from the octal socket so he wouldn’t get it wrong. Another run on the tube tester confirmed that everything looked good. After plugging the tube into the radio, it worked just as expected

If you need fabrication rather than repair, we’ve got you covered there as well. Check out [Charles Alexanian’s] process for making new vacuum tubes in his garage. Now if you just have too darn many of them around, you can always decorate your pad with ‘em.

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PortableSDR Makes It To Kickstarter

Last year’s Hackaday Prize saw a lot of projects that were crying out to be Kickstarter Campaigns, but non has seen people throwing money at their screens quite like [Michael]’s PortableSDR. It’s a small, handheld, battery-powered shortwave software defined transceiver that can do just about everything with coverage up to 30MHz. It’s the ultimate apocalypse radio, a contender for to the throne now held by the ‘my first radio’ Baofeng, and now, finally, a campaign on Kickstarter.

The PortableSDR (now called the PSDR) started off as [Michael]’s ideal radio. It just so happened the Hackaday Prize gave him the impetus design, develop, and build the radio that would eventually land him third place in The Hackaday Prize.

The radio itself is completely self-contained and battery-powered, implementing a software defined radio on an STM32F4 processor. The design includes an LCD for the waterfall display, vector network analysis, and the ability to receive GPS.

In keeping with its ham heritage, [Michael] is offering the PSDR as a kit, with a PCB, enclosure, and all the parts you can’t get on Digikey available for a $250 pledge. Get those toaster reflow ovens warm, because there’s a lot of SMD parts in this build.

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Using librtlsdr Over TCP

[Texane] built a low-cost software defined radio rig which could be remotely controlled. This allows the hardware to be placed outside for better reception, while being controlled from any PC that can connect over TCP. To do this, he created a fork of librtlsdr, the library used to turn cheap TV tuners into software defined radios.

The official release of rtl-sdr includes the rtl_tcp utility, which is meant for this purpose. Unfortunately, not all of the SDR tools for Linux support this. By modifying the library itself, remote devices interact with software in the same way as local devices. This means that any software that supports librtlsdr should work.

The outdoor rig contains a BeagleBone Black and the SDR hardware, sealed up in a weather-resistant box. This connects to [Texane]’s home network over ethernet, and allows SDR utilities to be run elsewhere.

This feature is quite experimental, but the source for the fork is provided for those who want to build the code and try it out.

Demodulating BPSK31 With OpAmps and 555s

BPSK31 is an extremely popular mode for amateur radio operators; it’s efficient and has a narrow bandwidth and can be implemented with a computer sound card or an Arduino. Just like it says on the tin, it’s phase shift keying, and a proper implementation uses a phase detection circuit or something similar. [Craig] thought it would be fun to build an analog BPSK31 demodulator and hit upon the idea of doing this with amplitude demodulation. No, this isn’t the way you’re supposed to do it, but it works.

Data is transmitted via BPSK31 with a phase shift of 180 degrees being a binary 0, and no phase shift being a binary 1. [Craig]’s circuit uses an op-amp and a pair of diodes to do a full wave rectification of the signal, which basically makes a binary 1 logic high, and binary 0 logic low.

This rectified signal is then fed into a comparator, making the output go high when the signal is above 2V, and low when the signal is below 1V. That’s all you need to do to get bits out of the signal, all [Craig] had to do after that was figure out a way to sample it.

A 555 set up in astable mode running at 31.25 Hz provides the clock, synchronized with the signal by connecting the comparator’s output to the 555 trigger input. The timer clock ends up being slightly slower, but thanks to the varicode character set, the maximum number of binary ones the circuit will see is nine; every time the trigger sees a zero, the timer’s trigger is reset, re-synchronizing the receiver’s clock.

Yes, it’s a hack, and no, this isn’t how you’re supposed to receive PSK. It does, however, work, and you can thank [Craig] for that.

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HamRadioTweets Gets the Word Out

In times of crisis, or extreme government control, it can be difficult to spread critical information to people who can help. A good example of this was during the Arab Spring in 2011. When your Internet connection is taken away, it can feel as though all is lost. Unless you have a ham radio, that is.

For many people the thought of ham radio conjures up images of old guys twisting knobs listening to static, but it’s actually come a long way in our modern digital age. For example, you can now send tweets via ham radio. This project was actually started in 2011 by [Bruce Sutherland]. The Egyptian government had shut down the country’s Internet access after citizens were posting information about the extreme violence they were facing. [Bruce] wanted a way to help  others get the word out, and he came up with HamRadioTweets. This system allows a user to send tweets via ham radio.

The system actually piggybacks off of a ham radio service called APRS. This service is most often associated with GPS tracking systems, such as those found in nearspace balloons, but it can also be used to send simple text messages over the air. APRS works thanks to the vast network of receiving stations setup all around the world. These stations can receive messages and then re-transmit them, greatly extending the reach of the original transmitter. Some of them are even hooked up to the Internet to get the messages to go distances that would be extremely difficult and unreliable by traditional means.

[Bruce’s] system hooked into the Internet component and watched for messages being sent specifically to “TWITR”. The Python based system would then read these messages and re-transmit them over Twitter. The project died out a while back after Twitter updated their API. Now, it’s been rebuilt on Ruby by [Harold Giddings]. The project website was handed over to [Harold] and he is currently maintaining it. Hopefully you’ll never need to use this software, but if the time comes you will be glad it’s available. You can watch [Harold] bounce an APRS message off of the International Space Station and on to Twitter in the video below. Continue reading “HamRadioTweets Gets the Word Out”

Old-Timey MP3 Player Blends Old Styling With New Technology

No, this isn’t the first commercial MP3 player ever produced. It’s a blend of the old and the new, old time looks with modern electronics. [viscomjim] recently made this MP3 Player from the ground up for the noble reason to give as a Christmas present.

[viscomjim] started by laying out a circuit using a solder-less breadboard to test his circuitry. He’s using PIC microcontroller to control the unit. There is an 20×4 LCD display, two rotary encoders with push buttons, a serial MP3 player module, real time clock and an infrared receiver. A wires-all-over mess wasn’t acceptable for this Christmas gift so [viscomjim] put on his learning cap and tried out Autotrax Dex PCB layout software. This was his first project with the software and everything went well. After the design was done, the board files were sent out to a fab shop. A few weeks later they were delivered. All the parts were wired up and tested and… it worked!

Next up was building a cabinet, this one was built out of wood and stained to give it a feeling of yesteryear. A pair of 4″ car speakers are responsible for sharing the tunes and are powered by a small amplifier and power supply mounted inside the enclosure. The front panel is laser cut clear acrylic and backed with a nicely prepared Photoshop’d parchment paper graphic. And those fancy grill covers, also laser cut acrylic, this time opaque brown in color.

There are only two knobs for control, the left is the volume and the right is the program changer. Push the left knob inward and the unit turns on or off, the right plays and pauses. This MP3 player plays music off the internal SD card on the MP3 module. [viscomjim] also went one step further and implemented some code to work with an Apple remote he had kicking around, hence the IR receiver mentioned above.

If you’d be interested in making something similar, you’re have-way there as [viscomjim] made his schematics available but, unfortunately, not his code. Want to build your own MP3 Player but want something a little smaller? Check this tiny one out.

‘Gibson Girl’ emergency beacon built from a Wind-Up Flashlight

Batteries flat and no cellphone coverage and you need to communicate hundreds of miles?  No problem. [Peter Parker VK3YE] has created a wind-up ham radio transmitter built into a discount store crank-handle flashlight (or torch). No batteries – all power comes from you turning the hand crank. This design was inspired by the ‘Gibson Girl’ emergency beacon transmitter used during Second World War. But what used to be an very large, full body cranking box is now tiny and simple to crank. Let’s take a look at he video and the build details after the break.

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