Homebrew Cylindrical Variable Capacitors: What the Steering Wheels are Controlling in Danny's Regen Receiver

Grayson KJ7UM asked a very good question about Danny ON1MWS's regen receiver:  What were those two very cool "steering wheels" actually controlling?.  

Perhaps because of our recent experience with Permeability Tuned Oscillators, I kind of assumed that we were talking about some form of variable inductor.  But no, I was wrong.  They are for homebrew variable capacitors.  That just makes it a lot cooler.  

Danny explains: 

Dear Grayson,

Tnx for the compliments. I used to build normal square boxes while I was a mechanic in a light advertisement factory. We had a one hour lunch break and were allowed to work for ourselves during the break. But I left that firm in 2019, as a consequence I had to find a way to build rigs without custom square boxes… the result is wood, tin cans of all sorts and a simple ground plate. After posting my CW rig on the FB group ‘the art HAM radio homebrew’ in 2023, Steve Fabricant noted ‘It could be a radiosonde that they sent down from a saucer to detect intelligent life, and failed.’ LOL, I found that very funny actually. 

 

As for your question, all of my homebrew tuning capacitors have a shaft made off a M8 (about 8mm) threatened rod. The rod turns through a steel girder bracket. I am not sure how these things are called in English, but they are easy to find on the net and very cheap. The rod is the ‘ground’ of the capacitor. The ground plate is clearly visible in the pictures of the solid state regen and the ground plate is hidden under the wood in the tube regen. In the case of the tube regen, the left tube has an inner diameter of 10mm and the right one about 13mm. The right one is coarse and the left one fine tuning. Not sure about the capacitance. 30pF at most I think. The tube regen tunes from 7 to 7.25 Mhz so that's ok.

As you turn the rod the rod will shift in or out the metal tube. The tube is obviously the ‘hot’ side of the capacitor. The M8 rod moves 1.25mm for one turn of the rod. If memory serves me right the tube is 80mm for the tube regen, so we have a tuning gear reduction of 80/1.25= 64. The hot side is connected to the main tuning coil to create a tank circuit.

I did try different designs before but this is the best one. The tube/treaded rod capacitor is just as good as a commercial one. One thing I learned is that any friction must be avoided in a homebrew capacitor or it is useless in practice.

I am going to try to build a similar 400pF version for a homebrew crystal set as I wrote to Bill. It will be huge I guess.. I think I will need a 2”tube… But my current homebrew projects are insulating our house better as our natural gas prices are rising.

Like the way you call tubes Thermatrons. Yes, sound much cooler and more fitting for these beautiful devices. My ultimate aim is building a one band thermatron SSB exiter. No time for the moment.

Kind regards Danny.

This technique could prove very useful in homebrew projects.  We found it very difficult to source suitable variable capacitors for our direct conversion receiver.  That is why we went with the PTO circuit.  But this technique makes it possible to actually homebrew the capacitors.  FB Danny.  

Thanks Danny.  Thanks Grayson.

ANOTHER AMAZING Homebrew Station -- This one from Belgium -- ON1MWS

 

Those large "steering wheels" on the regen rig caught my attention, and I'm glad they did, because they led me to the sites of Danny ON1MWS. 

https://www.qsl.net/on1mws/

https://www.qrz.com/db/ON1MWS

Danny writes on his QRZ page: 

I'm especially interested in homebrewing my own station. everything from the power supply to the antenna is scratch-build. I have no commercial ham gear, nor do I use pre-fabricated kits or DDS chips.

My gear is a toy compared to a modern station. And it will never even come remotely close to commercial gear. However, the journey to learn how radio circuits work, improve the station and add capabilities over the years has been satisfying. R&D as amusement.

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

FB Danny!  Thanks for the rigs and web sites.  73  Bill N2CQR

The Coastwatchers -- Their Rigs and Their Islands

 

AWA Teleradio 3BZ used by coastwatchers during the war Source: Australian War Memorial (P01035 .006)

Here is a great site about the AWA 3BZ Wireless set: 

https://www.qsl.net/vk2dym/radio/3BZa.htm . 

AWA 3B SET

Here's a good article about the Coastwatchers: 

https://www.military.com/daily-news/investigations-and-features/2025/12/22/former-school-teacher-led-guerrilla-army-behind-japanese-lines-solomon-islands-and-helped-us-win.html

Guadalcanal 1943

I've been interested in the Solomon islands lately because my wife and I have been watching a YouTube video channel about a family living on Uepi island: 

 https://www.youtube.com/c/TheIslandLifeofUs 

Uepi is right on "the slot," near New Georgia. 

There are WWII remnants still visible (underwater) at Uepi: 

AI Overview

Uepi Island in the Solomon Islands is famous today for its World War II history, particularly its abundant, accessible WWII wreck dives (aircraft & ships) in Marovo Lagoon, a key battleground during the Solomon Islands Campaign, offering divers a tangible connection to the fierce fighting between US and Japanese forces. The area, near major WWII sites like Guadalcanal, features underwater artifacts like Japanese Zeroes and US Corsairs, with the modern Uepi Island Resort preserving these historical relics within its dive operations. 

Uepi's WWII Significance

• Location: Uepi is situated in the Marovo Lagoon, part of the Solomon Islands, which were central to the brutal Pacific Campaign of WWII.
• Wreck Dives: The waters surrounding Uepi are a "treasure trove" of sunken WWII aircraft (like P39 Air Cobra, Japanese Zeroes) and shipwrecks, making it a prime destination for historical diving.
• Preservation: The Uepi Island Resort actively manages and promotes responsible diving at these sites, emphasizing that removing artifacts is illegal. 

Key WWII Sites & Wrecks Near Uepi

• Wickham Harbour: Located near Uepi, this area contains significant WWII wrecks, accessible via boat trips from the island.
• Aircraft: Divers can find Japanese Zeroes, American Corsair fighters, and potentially B24 bombers, often in challenging conditions, with efforts to move some to cleaner areas.
• Marovo Lagoon: As one of the world's largest saltwater lagoons, it holds numerous historical remnants from the intense fighting. 

A VERY Interesting Old "Steam Punk" Homebrew Thermatron Rig -- Can You Suggest A Home for this Rig? (Video)

Oh man.  They got me at the breadboard, but there was so much more:  

-- A mercury switch

--  A homebrew variometer

-- A reading lamp

-- A specially made (and stored!) tuning tool and a mechanical pencil 

--  A CQ paper tape and tape reader! 

-- A front panel clock

-- Space for QSL cards on the front panel   

This is a really cool homebrew radio!  Can someone find a good home for this amazing device?  The video was posted only 1 month ago.  

SolderSmoke Podcast 261: Travel, AI-Apocalypse, ARRL Award, Amplifiers (with Claude) , Transcoms, Smoke released in DR, QRP, CW, MAILBAG

SolderSmoke Podcast #261 is available for download: 

Audio:  http://soldersmoke.com/soldersmoke261.mp3

Video:  https://www.youtube.com/watch?v=1rzw8lxBzRo

Alaska, Colorado, Dominican Republic

Opening:   Travel notes:    Pete to Denver.  Dean to Alaska.  Bill in the Dominican Republic. 

The future of the podcast.  We will embrace our NIMCEL status and fight on in spite of the AI Apocalypse.   Thanks to Peter VK3TPM, Hamilton KD0FNR, Sam AI7PR, Todd K7TFC  and the WayBackMachine for providing backup and transfer options for the blog. Google could end Blogspot at any time.    

Dean and Bill win the 2025 ARRL Technical Service Award.  Thanks to Bruce KC1FSZ for the nomination. And thanks to Bill Morine N2COP for letting us know.  91 receivers completed so far!  

SolderSmoke East was pleased to host Phil W1PJE, a distinguished MIT radio astronomer AND member of the SolderSmoke Direct Conversion Receiver Hall of Fame.   

Dean:   Amplifier design,  woes, triumphs, tribal knowledge.  And help from Claude. 

KK4DAS 100W MOSFET AMP

Pete:  Project X  -- The Transcom SBT-3,  Crossroads and Decisions. 

Transcom SBT-3

SHAMELESS COMMERCE DIVISION:   FIGHT THE AI-APOCALYPSE -- BECOME A PATREON SPONSOR.

GET BEZOS TO SEND US BEZOS BUCKS!  Use the Amazon link on the upper right.   

BUY PARTS AND STUFF FROM MOSTLY DIY RF. 

Bill: 

-- Smoke released in TWO RD06 finals.  Scrounged IRF-510s to the rescue.   

-- Working VK6 on 20 SSB.  

-- My old HW-101 -- inspired by Pete and by Will N5OLA.   

-- High frequency hearing loss and direct conversion receivers. 

-- Eleven contacts on 40 with the DC RX and a Tuna Tin 2. Mike Bryce WB8VGE came back to my CQ! First ever QSO with SolderSmoke DC receivers on both sides:  K1OA-N2CQR.  

-- Do real hams use ALC? Do we really NEED ALC? 

Mailbag: 

Who is the Project 326 Guy?  A British engineer resident in China for last 20 years. 

Steve EI5DD  Ham Radio Ireland magazine.  Hey -- Why no Irish DC RX builders? 

Paul K9ARF -- Thanks for the very kind e-mail about SolderSmoke. 

Rogier PA1ZZ -- Many nice videos and suggestions on blog backup. 

Grayson KJ7UM on the EF-50 valve (thermatron!) 

Bruce KC1FSZ  Four DC RX builders at the Wellesley Mass radio club. 

Chris KD4PBJ -- Long trip to pick up two directional beacons possibly for 630m or 2200m bands! 

Alan W2AEW did a Minimum Discernible Signal test on the DC RX.  FB! 

Mike WN2A  -- Many great comments on MDS in its various forms. 

Philippe F6GUH is a FB homebrewer.  

Mike EIOCL -- Always great to talk on the air with an old friend. 

Walter KA4KXX -- I checked into the Sunrise net!  With my HW-101!  Thanks Walter. 

Farhan VU2ESE -- Watched our interview with Phil W1PJE

Phil W1PJE was an SWL with an old Halli receiver.  VOA?  Boo!  But Radio Marti is BACK! Also, the hydrogen line from the cosmic dark ages has red shifted to... 7.1 MEGA hertz!  So LISTEN UP! 

Phil W1PJE with a Halli and the Haystack Observatory Dome

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. 

Grayson Evans KJ7UM Interview at Four Days in May at the Dayton Hamvention 2025

 

LISTEN TO THE INTERVIEW HERE: 

http://soldersmoke.com/KJ7UM at Dayton 2025.mp3

Grayson said quite a lot in this short 4 minute interview: 

-- At FDIM he was selling his wonderful book "Hollow State Design for the Radio Amateur."  Buy one here: https://www.ermag.com/product-category/books/ 

-- Grayson was also selling a Thermatron version of our beloved Michigan Mighty Mite transmitter.  It is crystal controlled for the 40 meter band, but the Color Burst Liberation Army approves! Here is a wonderful video on this rig:

https://soldersmoke.blogspot.com/2024/09/excellent-new-video-from-grayson-kj7um.html

And be sure to watch Grayson's excellent course on Thermatron Homebrewing: 

https://soldersmoke.blogspot.com/2024/02/grayson-evans-kj7um-video-on.html

-- Asked why someone should build with tubes when so much good solid state stuff is available, Grayson makes some especially excellent points:  The solid state gear is often filled with mysterious little black boxes -- we often don't really know what goes on in there.  Thermatron construction provides a break from complicated SDR nonsense "that is not really radio."  That last comment will generate some criticism, but not from here.  I think Grayson is right,  He earlier expressed admiration for complex circuitry, but he also rightly defends simple, understandable rigs.  

Here are Grayson's Technical Documents (a real treasure trove):  https://kj7um.wordpress.com/

Three cheers for Grayson.  And thanks to Bob Crane W8SX for doing this interview.  

The Copasteic Flow Blog -- German UHF Mobile CW Through a Geostationary Satellite, Agent Sonya's Homebrewing, More

It is always good to be reminded that someone out there is listening and reading,  especially when it is nice folks like Hamilton and his family. These are the people who built the TouCans rig that was (is?) suspended above San Francisco at the center of a dipole antenna.  

Following posts on the SolderSmoke blog, Hamilton has been monitoring the CW activites of a German ham who sends UHF CW signals through the sunroof of his car to the QO-100 satellite in geostationary orbit.  See above.  Very cool.  Listen live to the satellite here: 

https://eshail.batc.org.uk/nb/

Also cool is Hamilton's analysis of Agent Sonya's ability to homebrew a 1930s era CW station that could be used to communiate with Moscow Center.  Hamilton believes she could do it.  I have my doubts.  But the discussion is a lot of fun. 

Check our their blog: 

https://copaseticflow.blogspot.com/

Thanks to Hamilton and his kids! 

"Seems Like Radio is Here to Stay" -- Old Radio, Radio Magic

The first 12 minutes of this podcast are pretty good.  I think it captures well the wonder of radio -- magic carpets, signals taversing the Himalayas and all that -- but the presentation is kind of confused.  The PRX podcasters keep saying that it was recorded in the 1930s, but then we hear references to the Nuremburg trials and the possibility of sharing the atom bomb. So there is some confusion in the presentation. 

https://podcasts.apple.com/us/podcast/champions-of-old-radio/id453044527?i=1000702716017 

Can anyone find the original recording from the 1930s about the wonder of radio, without the references to things that happened in the late 1940s? 

Thanks to Rogier for sending this to me. 

Norman Corwin

Victor's FB SolderSmoke Direct Conversion Receiver from Holland Pulls In Stations from All Over Europe... and One from Japan

Victor is a retired Electrical Engineer from the Netherlands.  He doesn't have a ham radio call sign, but as I have said about other receiver builders, he deserves one.   Note the truly homebrew approach that Victor used on the PTO coil form.  And he had to rebuild this part to get the receiver on 40 meters.  As we can see in the above video, Victor's homebrew receiver is pulling in stations from across Europe.  Victor even reports hearing a Japanese station.  FB! 

Victor writes:

Hi Bill, I changed the PTO tuning unit, more stable this way.   I m a retired electrical engineer, revamping on a more daily basis  tube radios from the 50's 😉 I include a Bluetooth interface too so they can be used again by "young" people with their smartphones..  I had great fun and learning experiences building the DCR !!  

Thanks for the video, pictures, and messages Victor.  Congratulations! 

For more information on how you too can build the receiver: 

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

 

Documentation on Hackaday:

https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

 

SolderSmoke YouTube channel:

https://www.youtube.com/@soldersmoke

Mr. Carlson Restores a BC-348 -- But 40 Meters Sounds Very Weak. Why?

Mr. Carlson mentions that he is a ham radio AMer.  He is also on SSB, but AM is, he says, his preferred mode.  FB. 

I got a real chuckle about the MVC switch position on the front panel.  "Manual Volume Control"  like "Manual Gain Control."  I thought I had invented this term.  You know, "real hams control their gain manually."  This is why Farhan never put AGC in the BITX20. But it seems the Army Air Corps was way ahead of me with the BC-348.    

Mr. Carlson makes it sound (!) like the Dynamotors are a thing of the past.  Not true.  Every Saturday morning I listen to the Old Miltary Radio Net and hear a number of Dynamoters spinning in the background.  One belongs to Buzz W3EMB who uses a BC-348.  Buzz has an SDR attached to the IF of his BC-348, which I think is an admirable mix of the old and the new.  Those BC-348s are, after all, quite old.  WWII old -- like 85 years old.  And still working.  

Paul has a good discussion of the importance of short lead length, and of mounting shielded capacitors properly, and of the usefullness of a good groundplane under the capacitor.  Go Manhattan boards!  Paul's presentation on how to identify the outside foil of a capacitor was very good, but I was wondering if you could also find out by using a file to remove some of the yellow insulation, then test with a DMM to see which terminal is connected to the foil. 

"Lots of times you have to add solder to remove solder."  Indeed. 

The importance of testing for BOTH capacitance and leakage.  Yes. 

But why bother with "period correct" internal wiring harnesses, when you have already put a bunch of modern caps in there?   I mean, I'm in favor of the re-capping, but this seems inconsistent with the need for "period correct" internal wiring harnesses. 

When Paul first fired up the receiver, I was hoping he would disconnect the antenna to see how much band noise was getting through. 

When Paul got to the IF alignment, he spoke of the dangers of working on energized high-voltage gear.  I had been thinking about getting a BC-348 myelf, but Paul's comments reminded me of why this is probably not a good idea for me.  Paul's comments about "knowing where your hands are" is on target.  "One hand behind the back, " is a good rule for this kind of energized testing -- this will help prevent current from a mishap from flowing through your chest.  

I may have more comments later.  Off to the beach now.  

Back from the beach:   

"Contrary to popular belief, the simpler the receiver, the better they hear."  Amen Mr. C. 

Paul's heroic cleaning of the 915 kc crystal made me feel like a wimp for not having tried to do this with some "bad" 455 kc rocks I was given while trying to build the Mate for the Mighty Midget receiver.  I may go back to those crystals and try to clean them as Mr. C did. 

The grand finale of this 2.5 hour video was, as expected, a demonstration of how good it sounds.  But unfortunately it did not sound good.  Paul tuned through the 40 meter band and I heard NO CW signals.  I didn't even hear FT8.   There were a few anemic SSB signals and, as he reached the upper portion of the band some very weak AM broadcast signals.  I didn't even hear CHU Canada's time signal.  Huh?  Why?   Our very simple homebrew Direct Conversion receiver sounds a LOT better than that.  I mean look at the sweep of 40 meters that I did using only a simple dipole:  https://soldersmoke.blogspot.com/2024/12/an-evening-bandscan-on-40-meters-using.html  Why is there such a big difference in performance? 

Could it be the antenna that Paul was using?   He was on what he calls the 369 antenna.   Could there be a problem in the receiver?  Could it be band conditions?   

A Tale of Woe from Mike WU2D, PLUS: The Importance of Band Noise

It was so cool to watch master homebrewer Mike WU2D candidly describe his error (tale of woe) made while building the Simple X Super receiver.  

It was also great to see his joy in hearing the band noise.  Watch his glee as the noise jumps up when he connects the antenna.  "That's the good stuff!"  Indeed it is.  So many younger builders see noise -- all noise -- as a bug not a feature.  Mike obviously sees it as a feature:  Thunderstorms in Brazil!  The weed-whacker down the street!  Remants of the Big Bang!  Hearing this stuff lets us know that the machine we have built is alive, and is inhaling the universe.  

Thanks Mike. https://www.youtube.com/watch?v=T_Mz9HljCys

 

What Homebrew Looks Like (And W9BRD comment on the High School receiver project)

Clikc on the picture for a clearer view of this fantastic image

Dave Newkirk is the son of Rod Newkirk, the guy who wrote the inspirational "How's DX?" column for QST for so many years.  Dave is obviously a very prolific and proficient homebrewer himself.  I really appreciate his comment on the High School receiver project.  Thanks Dave. 

Dave wrote on QRZ.com: 

Rummaging around the net for such phrases as "TJ receiver" or variations that include AA1TJ and receiver returns no solid hits, but by following clues I found a/the article with schematic at https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver. That's a well-thought-out design that'll provide fun, fun, fun.

I think I have something like 8 homemade receivers available at the moment at W9BRD, tube-based and solid-state, regenerative and superhet. all told covering 160 through 17 meters (if I include my tube-based and solid-state converters), and about the same number of homemade transmitters. With some exceptions for particular on-air celebrations and events, commonly my entire station lineup is homemade from stem to stern, so to speak.

I've been building radio gear since 1968. Here's some recent fun:

Zed thread covering the development of a converter-plus-regenerative-tuner combo that I came to call the "Super 3-in-9":

https://forums.qrz.com/index.php?th...ceiver-using-one-9-pin-miniature-tube.897249/

Zed thread covering construction of my version of a coffee-can-based receiver/converter combo my father used for 15ish years as his main station receiver after beginning its construction in 1951ish "on a kitchen table in Hartford" while working at ARRL HQ:

https://forums.qrz.com/index.php?th...building-a-160-meter-coffee-can-regen.938709/

To which discussion our own @N2EY kindly posted the mid-1960s "How's DX?" lead in which Dad laid out his station design/configuration/construction philosophy ( https://forums.qrz.com/index.php?th...0-meter-coffee-can-regen.938709/#post-7021505 ).

To us, commercial/mil/pro gear has been and always will be various shades of inspiring to fabulous, but only with homemade gear are we home.

A little Night Radio Romance at W9BRD, featuring the BRD-160CC 160-m regenerative receiver and converter (transmitter and antenna tuner not shown).