Project Epsilon: Linear Regulated Power Supply from Spare Parts

Belgian engineering student Gert-Jan built a great looking, and functional, linear regulated power supply for a test bench from an old radio transformer and a handful of supporting parts. This is a pretty nice looking adaptation of the common LM317-based power supply project. It only has a few parts and can make a nice, workable bench supply.

DSCN2848 - Copy

The supply uses an LM317 linear regulator. It can offer an adjustable voltage from 1.2-20V, since that’s the maximum output of the transformer, even though the LM317 itself is rated up to 37V. The case and meters came from eBay.


I do like what looks like a precision pot he’s chosen for the adjustment. I’d love to see a version of this build with a complimentary negative supply built around the LM337 as well. There’s plenty of room on that main piece of perfboard!

Making your own version of this supply would be pretty easy. Gert-Jan goes over the math of LM317’s adjustment range and includes schematics for each part of the system (rectifier and regulator). It’s up to you to string those two together, but that shouldn’t be very difficult. Transformers like that are pretty common, too. This would be a fun afternoon project. I might end up building one myself, I could use another adjustable supply. Maybe I’ll add a negative side to my version, too.

Project Epsilon

New Blog Link: JM Radio

I stumbled across this blog while browsing recently and just had to share. It’s similar to this one with more focus on transistor radios: JM Radio, based out of Indonesia. The author has quite a collection of transistor radios he’s worked on over the years, and has a handful of parts and radios for sale to interested collectors and technicians.

The entire site does happen to be written in Indonesian, but the automatic translation does well enough to understand what’s going on.

It’s a fun read, well worth dealing with the machine translation. There’s also some events write-ups and tech tips and tricks. Check it out!

JM Radio

Important Note About “Heartbleed”

This is a bit outside the normal repair shop posts you find here, but it’s important: A coding mistake that has existed for several years in one of the fundamental libraries used by about half of all servers on the Internet was recently discovered, and it’s likely being used to steal passwords and account information from all across the Internet. This is such a major issue it’s been given it’s own name, the Heartbleed bug. Companies are working frantically to secure their systems.


Mashable has some more comprehensive information, but if you use any of these services, you should change your password or your account may have been compromised:

  • Facebook
  • Instagram
  • Pinterest
  • Tumblr
  • Google (including Gmail)
  • Yahoo (including Yahoo Mail)
  • Amazon Web Services (but not Amazon Shopping)
  • GoDaddy
  • USAA
  • Intuit (TurboTax, QuickBooks, etc.)
  • DropBox
  • Minecraft
  • OKCupid
  • SoundCloud
  • Wunderlist

Be safe out there!

September Update

Welcome to KF7LZE! I’m an amateur radio enthusiast and freelance electronics technician. I write this site with a goal to make it easy and enjoyable to put together electronics projects and perform your own repairs to save money, have fun, keep electronics out of landfills, and maybe learn a thing or two along the way. I write up many of the projects I complete on this blog, take in many kinds of equipment for diagnostics and repair, and run a  joint venture to sell the kits and parts to complete the same projects and repairs yourself at home with another hobbyist.

There are a lot of articles – feel free to check out some of the various Antique Radios and other Projects – but here are some I picked out as interesting highlights:

  • Round-Up of RTLSDR UpconvertersA nearly comprehensive listing, with pointers for where to buy, for the most common and most desired HF converters designed to allow the reception of HF or 6m and higher radio signals using any RTL2383U-based DVT-B dongle.
  • Bose 901 Active Equalizer Repair and Bose Projects ListI bring the classic Bose 901 Series 1 speakers back to their best performance by rebuilding the equalizer with modern precision components to replace the originals which have almost universally failed and introduced distortion or outright failure into the system. Lots of photos, and parts kits are available as well.
  • 1st Generation Mazda Miata MX-5 Airbag Computer RepairBad capacitors can strike anywhere; in this case it results in a permanent Code 10 for the car’s SRS system. It’s a short and sweet process to replace them, and the thermal fuse which triggers the Code 10 error. Many readers have found this article helpful, although not everyone is up for attempting this particular repair.
  • Samsung 225BW Monitor Capacitor ReplacementThis model, and similar aged Samsung monitors, are known from the Internet for failing power supply capacitors starting a few years ago. It’s easy and cheap to restore full functionality, and is definitely worth doing for a nice quality LCD monitor like this one.
  • 1934 Simplex Model P “Dual Band” Antique Radio Restoration: Featured on Hack-a-Day, a dead old radio with quite a few problems and very challenging wiring sings again, with many photos of the entire process along the way.

Feel free to leave a comment or question, and thanks for stopping in!

Partsim: Circuit Simulation Made Easy

I came across Partsim, a free and easy to use circuit simulator that runs in the web browser, and would definitely encourage you to check it out if you’re looking for a tool to design and simulate circuits.

partsim snip


It supports a wide variety of components, and even supports Digi-Key integration to make it easy to buy your project once you’ve seen its results. That’s a great feature! Anything to take some of the pain out of generating a Bill of Materials is welcome in my book.

Check it out! Partsim

Listen to Ham Radio Online with the ETGD WebSDR

I just discovered the fascinating Wide-band WebSDR operated by the amateur radio club ETGD at the University of Twente in the Netherlands.

websdr board

PA3FWM built a fascinating wideband SDR using a Xilinx FPGA, high-speed ADC and gigabit Ethernet interface to receive most of the entire shortwave and amateur radio bands at once and allow tuning and processing in software via an HTML5 or Java web browser.

websdr capture

I’m listening to a station on 9760 kHz right now, which is broadcasting what sounds like classical choral hymns and dialog in Italian and Latin, so it could be a Vatican shortwave broadcast station. The interface is easy to use, and right now 142 users are tuning in from around the world.

It’s definitely worth checking out. I like shortwave listening but even with a great converter and my RTLSDR, my location just isn’t optimal for receiving the kind of signals I’m interested in – this web option is a lot of fun to go exploring.

Odd Web Site Behavior

I’m moving towards hosting the majority of my content on an on-premises server, versus the mix of hosted services I’m using currently. I’ve been running into some issues, though, that maybe one of you who is reading could help with…

The issue appears to be: some users, for no particular reason I’m able to identify, are unable to access any of my web sites.

My web domains are pointed at my server’s public, static IP address. The DNS records are valid, and DNS resolution works as expected always returning the correct address. The server responds to ping, and can complete a trace route. But, for users who this problem effects, it’s as if the server doesn’t respond. From my mobile device, for instance, I receive an Error 504 Gateway Timeout, the cell phone network’s caching proxy can’t receive data from my server. Port scanning reveals the ports are open and accepting connections on the server, but bonnection requests time out with no received data from a system on a Time Warner connection, as well.

This is all occurring while other users are logged in and actively using some services, so it seems unlikely to be an issue with the server itself failing. Even more vexingly, it’s intermittent. My mobile web site was working yesterday. It is not working today, from my cell phone.

If anyone has troubleshooting suggestions, I’d love to hear them.