SolderSmoke Direct Conversion Challenge: 139 Receivers Built

Dave M6XTY

As of September 28, 2026  1248Z

So far, total receivers built: 139 (131 plus 8 honorable mentions).  Total Count:  139.  Receivers built in 19 countries.   

NE3U (KY4EOD)  Matt 

KQ4AOP       First ham signals ever heard! 

N9TD             Derek

AC3NG          Ryan

VK3TPM       Peter Marks  

W4KAC         Ken 

W4KAC         Ken built a second one! 

N2EPE           Erik

VA3NCA        Wayde  (Canada)  

KI5SRY         Mark -- Gears on PTO screw

 

KA1MUQ       Frying pan receiver

AA1N              Adam

ZL1AUN         Aaron -- Using SSB transmitter -- (New Zealand)

W8UC             Never before homebrewed. 

VK4PG           Phil -- Nice case, "really pleased"

G7LQX           Working well, video of CW and SSB.  -- (England)

KE2AMP        John     Spring on PTO screw -- great

N9SZ              Steve  nice receiver

KD9NHZ        Piotr  Nice one

KE8ICE          Calvin, Very cool receiver. 

 

WV3V              Jayson!  Got it done!

GM5JDG         Martin.   -- (Scotland) 

KF8BOG          Jim:  A long struggle, but success.  

Chris Wales    Fantastic video.  -- (Wales)

YD9BAX         Wayan! Homebrew transformer!  (Indonesia)

N0NQD         Jeff 

WN3F              Roy -- Made new stickers! 

AB5XQ            Bill  

KB7ZUT          Andy  

AA1OF            Jer

VictorKees        Holland (Netherlands) 

KC9OJV           John -- Manhattan-style convert

WZ5M              1, 2 or maybe even 3 receivers!

K1KJW             Jim in Vermont

KC5DI              Dallas -- friend of WZ5M

Gary                 Australian -- Wooden PTO form (Australia) 

LU2VJM          Juan in Argentina  -- (Argentina)

K1OA               Scott "Most fun in 50 years"

KC9DLM         Ben -- Had EFHW problems

PH2LB             Lex  Yellow, Glue Stick -- (Netherlands)

AI6WR             David

G6GEV            Dave (It was a blast!)  (England)  

KC1ONM        Wayne  MakerLabs NH

KB1OIQ          Andy    MakerLabs NH

KA1PQK         Jay       MakerLabs NH

W1TKO           Mike    MakerLabs NH

K5KHK            Karl

SM0TPW         Mikael  -- (Sweden)

KI7LKB           Brian (coat hanger tube)

M6CRD            Chris  (England) 

W2DAB           Dave in NYC

W4JYK            Wes of VWS

KA4CDN          Mike of VWS

M7EFO             Adrian 

VK5RC             Rob  (Australia) 

KD8KHP          Dave

VK1CHW         Chris (Australia) 

KA0PHJ           Brian

W0IT                Louis

W1PJE             Phil

W2AEW           Alan

KN6FVK          John (Barkhausen-Be-Gone Spray) 

VU2JXN           Ramakrishnan -- (India)

AA0MS            Doug 

9V1/KM7ABZ   Paul  --  (Singapore)

VK2BLQ          Stephen -- (Australia)

N3FJZ              Rick

Daniel               VE5DLD  -- (Canada)

Student 1          Student of VE5DLD

Student 2          Student of VE5DLD

Student 3         Student of VE5DLD

K7WXW          Bill 

NK3H               Mitch

KN4ZXG         Ted

WA1MAC        Paul

N4AVC             Chuck 

K3IY                 Kevin

N6ASD             Ashish in Bangalore (India)

W1DSP             Rick

WD4CFN         Steve

KM5Z             Mike

KF5DAN         Dan

Fritz                 Fritz

N9OK              Joe

WA5DSS         Bill 

K0GDB           Grant

G0JNR            Shane Glow-in-Dark Coil Form

KK7BCO        Tobias

K2BVR            Bob

Robert              Sutton

K5YFO           Dave (Texas) 

KD4PBJ          Chris

KN4GAH        Chris -- EE perspective

F1GMA           Philippe  -- (France)

W2TEF            Todd

EI9ITB            Karl  -- (Ireland)

VU2TUM         Puneit Singh (India) 

AA7EE             Dave Richards

KI5VIR            Jay

CT7AXD       Graham -- Promoted from Honorable Mention! (Portugal)

G3MOT           Josh (England)

KW4H             Steve

NJ7V                Charlie (RedSummit)

N2ETZ            Denny

AB9LM           James

W9XT              Gary

G0PJT             Alex

KF8FZZ         Tyler

N7HPR           Steve (Instructor) (N7HPR Group)

Clark               (N7HPR Group)

KQ4ZHO        Kurt (N7HPR Group)

KQ4OBR        Brian (N7HPR Group)

KR4CUF         Justin (N7HPR Group)

Amanda          (N7HPR Group)

David               (N7HPR Group)

KM4AED       Jamey (N7HPR Group)

KN4MVH      Larry (N7HPR Group)

N5GVW          Dick (N7HPR Group)

W7KAL          Kal

KC9LFP         Joe

SP9DEL         Marian (Poland) 

LB8VA           Ivar (Norway)  

AA7FO          Chuck Adams! 

WE6Z            Doug

N7MN            Jason

VA2GJ           Gerald in Quebec

N6HA             Bill 

Andri             Bandung, West Java, (Indonesia)

K6AUS          Scott

Brett K          Tasmania (Australia) 

Dave             M6XTY 

 

-------------------------

Honorable Mentions: 

*AA7U            Steve No PTO

*VK7IAN        Ian -- No Manhattan boards -- (Tasmania)

*KC1FSZ        Bruce's build on a PC board

* DL1AJG      Andreas -- (Germany)

* Matthew      Student of DL1AJG

* Arash           Student of DL1AJG 

*KA4KXX     Walter -- FB 20 Meter version

*M9KCA-ST2NH  Nader - LM386 in place of AF amp

Grayson Evans' Modest Proposal: NO MORE VALVES! NO MORE TUBES! THERMATRONS FOREVER! (and a great video)

First, a big THANK YOU to Grayson KJ7UM and to Zeynep, his wife and video editor.  The above video is a really excellent look at not only the technical characteristics of thermatrons, but also at the history of their development.  There is a lot to be learned in this wonderful video. I am glad that no one was shocked in its production. And I am glad that SolderSmoke is no longer the only podcast/videocast using a "shamless commerce" segment! 

Grayson's video and his "modest proposal" are eerily timely for me.  Just yesterday I dragged out my old thermatron 80/40 receiver and got it inhaling.  It uses 6U8s and 6EA8s which were featured in this video.  This morning I used this old thermatron receiver to listen to Tim WA1HLR, who has been using thermatrons for many years. 

I have also been talking about Compactrons -- specifically the 6T9 -- on the podcast.  This prompted Jeff Tucker, W9TH to send me the PC board for the simple 6T9 circuit that I should have built as a teenager.  I also got words of encouragement from Mike WA6ARA.  The pressure is building!  

Finally, this gets us to Grayson's "Modest Proposal."  See:  https://kj7um.wordpress.com/2026/09/16/a-modest-proposal/    He proposes that we STOP calling these devices "tubes" or "valves" and instead refer to them as thermatrons.  I am with him on this.  But I warned him that his proposal (even with modesty) would provoke HOWLS of protest from the many, many change-averse radio amateurs in the US and, especially in the UK.  I know from personal, lived experience (four years in London) that the Brits love their valves.  But, hey, Grayson is right!  So I will pledge -- whenever possible -- to use his preferred term.  Gentlemen, don your Kevlar now!  

Thanks Grayson for the video, and for the modest proposal!  

Get the Third Edition of Grayson's excellent book "Hollow State Design"  here: https://www.hollow-statedesigns.com/books

Other Workshops: Zen and the Art of Model Making -- Please Comment

This one may seem a bit far off our normal path, but I think this fellow has a lot of philosphy that applies to ham radio homebrewing.   His story of the art teacher who advised his students to get up each morning and do something that you love to do is good advice.  

What other advice and philosophy did you hear in this beautiful video? 

"Solvitur ambulando." Latin for "It is solved by walking."

We've been proponents of this idea for a long time:  Essentially it is that sometimes you have to at least temporarily put a hard technical problem on hold.  Sometimes you need to just STOP working on the problem, put the rig on the shelf, and go out and take a walk.  Or, perhaps, a hike. 

In the travel section of the New York Times today, I found this phrase from Latin: "solvitur ambulando."  It was in an atricle by one of my favorite authors, Paul Theroux. One of his his novels, "The London Embassy" was eerily true to life, and had me thinking that the house he described was, in fact, the house in London that I was living in.  Paul has been at it for so long that, frankly, I thought he was gone.  I was delighted to learn that he is not, and that he is still writing books. 

Theroux wrote, "Is something fuddled in your mind? Searching for an idea? Then lace your boots, leave the house, and set off alone: Chances are you will find the answer along the way.  This remedy (attributed variously to Diogenes the Cynic and St. Augustine) is one that all true piligrims know, and in many respects serious hikers are the modern embodiment of medieval pilgrims."  

Indeed, if the solution is fuddled in your mind and you are searching for an idea, take a break, do something different.  Take a walk: "solvitur ambulando." 

Fixing up a Nice Old (but not TOO old) Receiver in the UK -- What would you have done? Please comment below.

Crikey! Blimey! The parts are wonky!  Then he fixes it and they are all lovely!  These are some great descriptive words that you just won't hear in a U.S. workshop.  Pity.  

I liked the receiver.  I had never seen one of these. 

The Ultrasonic cleaner was nice.  As was the oven.  

His repair of the switches was very cool.  I like his technique for repairing the many leads that got broken. 

When he started unplugging the plugs on the boards, I got nervous.  Pull out the cell phone and take some pictures first!  

Opening up those old pots was really going the extra mile.  I would have just squirted some deoxit in them.  

He ended up changing almost all the caps on the AF amplifier board.   The Capacitor Police would indeed been annoyed.

Great job.  It was fun watching him work.  But what would you guys have done differently?  Please comment below. 

Thanks to Rogier PA1ZZ for sending me this. 

Soft Power and Shortwave Radio -- A BBC Program on the History of Shortwave Radio

 

https://shortwavearchive.com/archive/bbc-radio-4-the-sound-of-soft-power-may-23-2026

I was reminded that SolderSmoke Mailbag might have its roots in Radio Moscow!  

And I was delighted to hear Thomas Witherspoon K4SWL explaining shortwave radio and propagation.   

Thanks to Paul VK3HN for sending us this link.

UK Homebrew VHF Matchbox Bugs

There is a lot of interesting tech in these little boxes:  

-- The way they are powered (hearing aid batteries). 

-- The way they are modulated.  

-- The way they use a weather radio to receive the signal.  

-- The very simple on/off switches.  

It is all very cool.  

Thanks to Chuck WB9KZY for sending this video to us. 

First QSO by Chris (aka Morny) G7LQX and it was Homebrew CW!

I must have missed this five months ago, but better late than never: Congratulations to Chris G7LQX for his first ham radio contact.  And he was using a homebrew CW transceiver. 

Details here: https://www.qrz.com/db/G7LQX  

Chris has a very nice fist, and he is one of the only YouTubers I have seen who holds the straight key properly, with his forearm resting on the table.  All of the others seem to keep the forearm floating in the air, above the key. 

School for Danger -- the SOE, and Radio, in Nazi Occupied France

Hack-a-Day had a link to this film.  It is really good.  There is some stuff about radio, and especially the S-Phone system.  But the bigger message of the film is the danger faced by the heroic teams who parachuted into occupied France.  As shown in the film, many of these people were young women who risked it all in the most dangerous of airborne operations.  It is a reminder of how ridiculous the focus on masculine valor in airborne and special operations really is.  Three cheers for the SOE. For all of them. 

A Very Impressive Workshop from the UK

This one is almost scary.  There is an amazing number of machines crammed into that workshop.  There is even more stuff in the drawers down below.  Honestly, I sometimes thought that we radio homebrewers would be the worst offenders in this regard, but I see here that most of us are not even close.  This guy wins!  

At the end, at about the 24 minute mark, he demonstrates the use of a "scissor table" that can be used to bring the item he is working on to the needed height.  That is pretty cool, and would be quite useful for those working on really heavy gear -- think DX-100s or R-390As.  I have heard of hams installing small cranes in their shacks to move these heavy boatanchors around (they do seem to get heavier with time!).  The scissor table would take care of this.  

After showing the scissor table, he hits a button and an empty work table top drops from the ceiling to cover the scissor table.  Very cool.  Very useful.  

One note of caution.  I found myself worried about all those propane torches that he seemed to have stashed in odd corners of the workshop.  I would be worried about the danger of fire.  It might be wise to add a fire suppression sytem to the impressive inventory of gear in that shed.  

Sorry for that nanny-state suggestion.  That said, this workshop is magnificent.  Three cheers for the owner.  

Nader M9KCA-ST2NH's Beautiful Build of the SolderSmoke Direct Conversion Receiver: NO SMOKE!

 Nader wrote: 

Hello everyone! After more than 30 years, I've rebuilt the DCR again. I wanted to share the fun of the 40m SolderSmoke DCR Challenge with all of you. It was a fantastic project — fully documented, with many people sharing their experiences online. I'm truly delighted to show you my prototype. The best part? It ran from the very first power-up — no smoke, no tuning needed! Yes, all on one board. The audio amp isn't quite ready to challenge the role yet, but it's still a lot of fun.

Nader's Sudanese callsign rang a bell with me.  I had talked about him in SolderSmoke podcast #58 on May 13, 2007.  Here it is:  https://www.soldersmoke.com/soldersmoke58.mp3    And I included a long quote from him in the SolderSmoke -- Global Adventures book.  So Nader is an old friend indeed.  

He clearly built the receiver, with excellent results.  He used the innards of a glue stick to build the support for the PTO inductor.  But he has not yet built the three-transistor AF amplifier.  So, in the interim, I am placing him in the "Honorable Mention" category.  When he completes the AF amplifier, he will be promoted to full membership in the Hall of Fame. 

Rex Harper on the 50th Anniversary of the Tuna Tin 2 -- DONATIONS NEEDED!

I was really pleased to see Rex Harper W1REX on a special edition of the RedSummitRF video podcast:  

 https://www.youtube.com/watch?v=SUQE4OvkAtU

Rex provides a lot a great background info on the Tuna Tin 2.  We are approaching the 50th Anniversary of the publication in QST of the Doug DeMaw article that launched the TTT revolution.  Rex has the original TTT in his possession, and is organizing a 50th Anniversary tour. We can only hope that much Mojo will be dispensed. 

I built one in a real tuna can:  https://soldersmoke.blogspot.com/2014/05/fdim-midnight-mojo-ceremony-tuna-tin-2.html  I still have the board! 

And above you can see Rex allowing the Mojo of the original TTT to flow into my homebrew 17 meter BITX (2014).  Rex and Charlie talked about this ceremony in the video cast.  Very cool. 

Rex is making available a 50th Anniversay edition kit of the Tuna Tin 2.  Get yours here: 

https://www.qrpme.com/?p=product&id=50A

Also,  Rex needs some help in financing a Tuna Tin 2 world tour.  YOU CAN HELP!   No need to limit your donation to 1 dollar.  Donate here!  https://www.qrpme.com/?p=product&id=WWT

Thanks Rex, thanks Charlie! 

"Keep Calm and Solder On"

 

So not everything that comes from AI is bad. This AI generated picture is pretty good.  That actually looks a bit like my rig.  And as someone who has spent four years in the UK, I can really appreciate the "Keep Calm and Solder On" sign.  Indeed.  Words to live by my friends!  

Why I can listen to both sides of VK-G Long Path QSOs in the Dominican Republic

Bottom line:  I think when Australians talk to Brits via long path,  in the Dominican Republic I am between the two. Both have their beam antennas aimed (generally) un my directions.  With an omnidirectional antenna (my 1/4 wave vertical) I can hear them both.  While they are on the Long Path to each other, I am Short Path to both of them. 

Here is my log entry (From the Dominican Republic): 

August 20, 2025 

20S around 0830 UTC  VK5UK Rich and G2YT Peter.  Rich was in LP contact with Peter  My  VFO was moving as the air conditioner kicked in.  I think I was hearing both of them SP.  With VK5UK I was off the side of his beam.  Same with Peter G2YT.  

---------------------------- 

Peter G2YT wrote:  

Yes, Rich and I were working Long Path… I was beaming at the top end of South America (about 240 degrees) and Rich was beaming approx 120 degrees.

------------------------------

Rich, VK5UK wrote: 

Hi, thanks for the email... My beam heading was around 150 degrees from VK long path to Europe you would have been receiving me via the shortest path between us, and I suspect you were being received by Peter on the same path? 73 Rich

------------------------------

Here is a good website that describes (using Australia to Europe) the Long Path and Short Path propagation paths:  

https://www.pa9x.com/long-path-or-short-path-propagation/

Here is a link to Google's new AI (on this subject) 

Shane G0JNR's FB SolderSmoke Direct Conversion Receiver -- With a Glow-In-The-Dark PTO Coil Form

I was really pleased to see Shane G0JNR finish this receiver. He has been an active member of the SolderSmoke community for many years.  For example, back in 2018 we see him commenting on KU4NO's FB rig: 

https://soldersmoke.blogspot.com/2018/07/a-rig-with-maximum-soul-5-band.html

Shane writes: 

Shane G0JNR here. I've just got my Soldersmoke DC rx up and running! The thing that put me off earlier in the year was the 3d printed coil former. But my son has now got one and printer and printed one for me - as an added bonus, it glows in the dark! It didn't work straight away but perseverance has paid off. 73

Thanks Shane! Congratulations and Welcome to the Hall of Fame.

Glow-In-The-Dark PTO Coil Form

The Guy with the USB-powered X-Ray Machine -- The Identity of the Project 326 Builder

This morning a comment came in from Hong Kong/Shenzhen that explained who Project 326 is and why he was saying "tubes" and not "valves": 

--------------------

Thank you for featuring my video. Some background for you, I am a British engineer and have lived in China for over 20 years. I am resident in both Hong Kong and Mainland China (Shenzhen, which is just over the border from Hong Kong). I used the term vacuum tubes as most of the viewers are from the US and us Brits are fully conversant with both terms, but in the US, they are often less 'bilingual' in these kinds of phrases.

Hope that helps!

----------------------

It does indeed help a lot.  Please continue to make great videos like the one about the USB X-Ray machine.  

Here is the channel: 

https://www.youtube.com/@project-326

Britain's EF-50 Valve (Tube, Thermatron) in WWII

Thanks to Rogier PA1ZZ for sending us this. 

Britain's Secret Listeners

Today Hack-A-Day has an unsually good report on Britain's Voluntary Interceptors. I was especially touched by the story of the guy who provided reports while still bedridden from devastating wounds received in World War I. 

https://hackaday.com/2025/06/12/crowdsourcing-sigint-ham-radio-at-war/#more-786810

I've had the video on the SolderSmoke blog several times.  It is so good that it warrants inclusion yet again: 

https://www.youtube.com/watch?v=RwbzV2Jx5Qo&t=228s

That regen looks a lot like the one I bought at the Kempton Park rally (London) so long ago.  I still have it.  And those headphones found in the old "radar" station look a lot like some that I have in my shack today.   And of course there is that HRO dial.  I build a whole receiver around that gem from Armand WA1UQO.  

I thought the comments on the ability to detect the nationality of the enemy operator from his Morse Code "fist" (sending style) was very interesting.  

Three cheers for the Voluntary Interceptors!  

Hiss, Filters, QRM, and Hearing Loss: Do we need AF filters in direct conversion receivers?

L6 is the 88mH toroid

Messages on Discord about the need to knock down higher frequency audio response in the SolderSmoke direct conversion receiver got me thinking.

I agree with Rick Campbell and others on the benefits of hearing a "wide open" direct conversion receiver. But Rick and others have built DC receivers with 3 kHz low pass AF filters. This made me ask myself a question: Is an audio filter in a direct conversion receiver a good idea?

And I started wondering if perhaps I was being too dismissive about the complaints about high frequency audio -- I had been attributing them to newcomers who were just unaccostomed to radio noise or "static." But maybe there was more to it than that. Maybe a big part of the problem was in my head, specifically in my ears. So this morning I did an experiment. I took an online hearing test. First, without my hearing aids: As expected, it showed significant high frequency loss. (It was as if the US Army had installed a 3 kHz audio low pass filter in my head!) Then I put my hearing aids in and retook the test: This time I passed the test and showed no loss. I then listened to the DC receiver with my hearing aids in. Now I could hear what builders on the Discord server were commenting on: I could hear higher frequency hiss, and, more importantly, stations that were producing 4-5 kHz sounds on my speaker were audible and annoying.

So I went back to Wes Hayward's November 1968 QST article. In his receiver, he has a low pass AF filter using an 88 MILLIHenry coil and a couple of capacitors to ground. I had a few of the coils (given to me years ago by a NOVA QRP club member) so I built it. With my hearing aids in, I noticed an immediate improvement. I then did what one of the Discord builders did and put the filter in with a switch that would let me make "with and without" comparisons. The filter definitely cuts down on any AF above about 3.5 kHz. And it doesn't seem to do damage to the desired signal. This is useful. I left the W7EL diplexer in the circuit.

This filter won't solve the image or "opposite sideband" problem inherent to simple DC receivers, but it will help with signals or noise that are producing tones above about 3.5 kHz in the receiver. I think this is especially important in countries in which there is a lot of SSB crowding on 40 meters. The UK, for example, has an allocation from 7.0 to 7.2 MHz. In the US we go from 7.0 to 7.3 MHz. That is a big difference.

So the answer is probably yes, an AF filter in a direct conversion receiver is probably a good idea, especially if you can switch the filter out of the receiver. You can live without these filters. Not having the filter keeps the receiver very simple, and lets it sound really great. But having the filter in there does help reduce interference and high frequency hiss. So I think this is a useful add-on mod for builders who see a need to cut down on the kind of interference that a lack of this filter causes.

In 2019 W7ZOI noted: "Another unusual element is the 88 mH toroid used in the audio low pass filter at the detector output. A viable substitute would be a 100 mH inductor with radial leads. The muRata 19R107C (from Mouser) should work. Bourns also offers a variety of similar parts."

Adrian M7EFO's FB SolderSmoke Direct Conversion Receiver

Adrian has completed a very FB direct conversion receiver.  Really nice work. It is especially pleasing to see that Adrian is a member of GQRP.  FB Adrian. SSB above, CW in the video below.  I think that China Radio International signal would be a good early target for your tinkering and mods.  We fought a similar battle against Radio Marti.  

Adrian writes:  

Did it!!! It Works.! Receives CW, SSB,FT8. Awesome. Thanks Bill. Thanks Dean. It was fun. Now for the tinkering and modifications.

CW too. As an added bonus it picks up China Radio International radio whether I like it or not.😄

Hello. I live in East Barnet a suburb of London, UK.

I work as an electronic technician and tech support for a small company. 

My rig is a Xeigu G90 with a home made dipole cut for 20 metres and 40 metres and run QRP at 5-10 watts, 5 watts FT8, I'll save the kilowatts for boiling the kettle!  I'm using an old PC server power supply. 

The shack computer is a Raspberry Pi3 Raspberry Pi400 (Stolen Borrowed from my daughter). I am surprised at how well my set up works. Sometimes.

I am a member of the GQRP club and have started building some kits and homebrew in the Manhattan style. 

Currently studying for my UK Intermediate licence with Bath Based Distance Learning.