This Board Helps You Prototype Circuits With Tubes

September 14, 2025 by Seth Mabbott 9 Comments

There you are at the surplus store, staring into the bin of faded orange, yellow, red, and black, boxes–a treasure trove of vintage vacuum tubes—dreaming about building a tube amp for your guitar or a phonograph preamp for your DIY hi-fi sound system. But, if you are not already in possession of a vintage, purpose-built tube testing device, how would you test them to know whether they are working properly? How would you test out your designs before committing to them? Or maybe your goal is simply to play around and learn more about how tubes work.

One approach is to build yourself a breadboard for tubes, like [MarceloG19] has done. Working mostly with what was laying around, [MarceloG19] built a shallow metal box to serve as a platform for a variety of tube sockets and screw terminals. Connecting the terminals to the socket leads beneath the outer surface of the box made for a tidy and firm base on which to connect other components. The built-in on/off switch, fuse and power socket are a nice touch.

[MarceloG19’s] inaugural design is a simple Class A amplifier, tested with a sine wave and recorded music. Then it’s on to some manual curve tracing, to test a tube that turns out to be fairly worn-out but serviceable for certain use cases.

If you’re dipping your toes into tube-based electronics, you’re going to want a piece of equipment like this prototyping board and [MarceloG19’s] documentation and discussion are a good read to help get you started.

Once you have your board ready, it’s time to move on to building a stereo amplifier , a tube-based headphone preamp, or take things in a different direction with this CRT-driven audio amplifier.

6502 Puts On An SDR Hat

September 11, 2025 by Bryan Cockfield 11 Comments

The legendary 6502 microprocessor recently turned 50 years old, and to celebrate this venerable chip which brought affordable computing and video gaming to the masses [AndersBNielsen] decided to put one to work doing something well outside its comfort zone. Called the PhaseLoom, this project uses a few other components to bring the world of software-defined radio (SDR) to this antique platform.

The PhaseLoom is built around an Si5351 clock generator chip, which is configurable over I2C. This chip is what creates the phase-locked loop (PLL) for the radio. The rest of the components, including antenna connectors and various filters, are in an Arduino-compatible form factor that let it work as a shield or hat for the 65uino platform, an Arduino-form-factor 6502 board. The current version [Anders] has been working on is dialed in to the 40-meter ham band, with some buttons on the PCB that allow the user to tune around within that band. He reports that it’s a little bit rough around the edges and somewhat noisy, but the fact that the 6502 is working as an SDR at all is impressive on its own.

For those looking to build their own, all of the schematics and code are available on the project’s GitHub page. [Anders] has some future improvements in the pipe for this project as well, noting that with slightly better filters and improved software even more SDR goodness can be squeezed out of this microprocessor. If you’re looking to experiment with SDR using something a little bit more modern, though, this 10-band multi-mode SDR based on the Teensy microcontroller gets a lot done without breaking the bank.

Reverse Engineering A (Toy) Fire Engine

September 6, 2025 by Al Williams 3 Comments

Your kid has a toy remote control fire truck. You have an RTL SDR. See where this is going? [Jacob] couldn’t resist tearing into the why and how of the truck’s remote control protocol.

The entire process began with a basic GNU Radio setup to determine the exact frequency of the signal. Then a little analysis suggested that it might be using amplitude shift keying. That is, the information is in the amplitude of the signal, where one possible amplitude is completely off in some cases.

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Optimizing VLF Antennas

September 4, 2025 by Al Williams 12 Comments

Using digital techniques has caused a resurgence of interest in VLF — very low frequency — radio. Thanks to software-defined radio, you no longer need huge coils. However, you still need a suitable antenna. [Electronics Unmessed] has been experimenting and asks the question: What really matters when it comes to VLF loops? The answer he found is in the video below.

This isn’t the first video about the topic he’s made, but it covers new ground about what changes make the most impact on received signals. You can see via graphs how everything changes performance. There are several parameters varied, including different types of ferrite, various numbers of loops in the antenna, and wire diameter. Don’t miss the comment section, either, where some viewers have suggested other parameters that might warrant experimentation.

Don’t miss the 9-foot square antenna loop in the video. We’d like to see it suspended in the air. Probably not a good way to ingratiate yourself with your neighbors, though.

Between software-defined radio and robust computer simulation, there’s never been a better time to experiment with antennas and radios. We first saw these antennas in an earlier post. VLF sure is easier than it used to be.

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The (RF) Sniff Test

August 29, 2025 by Al Williams 11 Comments

Sometimes the old tricks are the best. [Kevin] learned an old trick about using a ‘scope to sniff RF noise and pays it forward by sharing it in a recent video. He uses an oscilloscope. But does he need some special probe setup? Nope. He quickly makes a little RF pickup probe, and if you have a ‘scope, we’re pretty sure you can make one in a few seconds, too.

Of course, you can get probes made for that, and there are advantages to using them. But the quick trick of quickly and non-destructively modifying the existing probe to pick up RF means you always have a way to make these measurements.

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Receiving Radio Signals From Space Like It’s 1994

August 28, 2025 by Bryan Cockfield 19 Comments

For certain situations, older hardware is preferred or even needed to accomplish a task. This is common in industrial applications where old machinery might not be supported by modern hardware or software. Even in these situations though, we have the benefit of modern technology and the Internet to get these systems up and running again. [Old Computers Sucked] is not only building a mid-90s system to receive NOAA satellite imagery, he’s doing it only with tools and equipment available to someone from this era.

Of course the first step here is to set up a computer and the relevant software that an amateur radio operator would have had access to in 1994. [Old Computers Sucked] already had the computer, so he turned to JV-FAX for software. This tool can decode the APT encoding used by some NOAA satellites without immediately filling his 2 MB hard drive, so with that out of the way he starts on building the radio.

In the 90s, wire wrapping was common for prototyping so he builds a hardware digitizer interface using this method, which will be used to help the computer interface with the radio. [Old Computers Sucked] is rolling his own hardware here as well, based on a Motorola MC3362 VHF FM chip and a phase-locked loop (PLL), although this time on a PCB since RF doesn’t behave nicely with wire wrap. The PCB design is also done with software from the 90s, in this case Protel which is known today as Altium Designer.

In the end, [Old Computers Sucked] was able to receive portions of imagery from weather satellites still using the analog FM signals from days of yore, but there are a few problems with his build that are keeping him from seeing perfectly clear imagery. He’s not exactly sure what’s wrong but he suspects its with the hardware digitizer as it was behaving erratically earlier in the build. We admire his dedication to the time period, though, down to almost every detail of the build. It reminds us of [saveitforparts]’s effort to get an 80s satellite internet experience a little while back.

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How’s The Weather? (Satellite Edition)

August 22, 2025 by Al Williams 2 Comments

When [Tom Nardi] reported on NOAA’s statement that many of its polar birds were no longer recommended for use, he mentioned that when the satellites do give up, there are other options if you want to pull up your own satellite weather imagery. [Jacopo] explains those other options in great detail.

For example, the Russian Meteor-M satellites are available with almost the same hardware and software stack, although [Jacopo] mentions you might need an extra filter since it is a little less tolerant of interference than the NOAA bird. On the plus side, Meteor-M is stronger than the NOAA satellite on 1.7 GHz, and you can even use a handheld antenna to pick it up. There are new, improved satellites of this series on their way, too.

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