Dave Richards AA7EE

January 27, 2015

Aaron N9SKN’s Sproutie Regen Receiver

I was quite excited when Aaron N9SKN told me he was building a Sproutie. Sometime earlier, I had discovered his website, billed as the “Home Of The 500mA Sidetone Oscillator/Shack Heater” I was searching for information on building HF receivers, and came across Aaron’s build of W7ZOI and K5IRK’s Progressive Receiver, as described in the Nov 1981 issue of QST, and the ARRL handbook for several years. Look at the pictures of the boards that Aaron made for the project in this article. Good stuff!

Aaron’s Sproutie build must have been a breeze for him in comparison. What a beaut. I’m wondering what material he made the front panel from. Is that garolite or something similar, or is it foam-core board? He did a great job of cutting the oval hole for the speaker. I like the “oxblood” color of the phenolic tube bases too – the same color as the Doc Marten’s I wore as a young man 🙂


“The Sproutie” as built by Aaron N9SKN. Photo courtesy of N9SKN

Aaron already had a Cardwell 2 x 35pF tuning capacitor in his “junk” box. It was still unused, which is why I put quote marks around the word “junk”. I am often amazed at the number of these lovely old vintage parts that have yet to be used in a project – it’s a great thing for us home-brewers. You can see it in this rear view of the receiver. Note the aluminum plate he installed behind the front panel to minimize hand capacitance effects. I’m looking at those leads from the tube base and the variable capacitors to the circuit board, and wondering if he gets any microphony effects –

Rear view of N9SKN’s “Sproutie”. Photo courtesy of N9SKN

A view of the underside, showing that oval speaker –

The underside of N9SKN’s “Sproutie”. Photo courtesy of N9SKN

Aaron is a hardier soul than me, as he made his own Manhattan pads. Here’s a view of his RF board –

The RF board in N9SKN’s “Sproutie”. Photo courtesy of N9SKN

Nice job Aaron. He posted 5 videos of his Sproutie in action too. Here’s one of them, showing his Sproutie in action on the 25M band. You can find the other videos of his Sproutie on his YouTube channel –

One of the enjoyable things about sharing pictures and descriptions of my activities in this blog, is hearing from builders like N9SKN. It’s great to know there are other people out there building things. I am occasionally tempted to spend my money on a commercially-made HF receiver instead, but I wouldn’t have anywhere near as much fun. Thanks very much for sharing details of your Sproutie build Aaron!

PS – Allow me to rave about Aaron one more time. He scratch-built a K8IQY 2N2/20 Manhattan-style. Major respect!


January 24, 2015

National Radio Company Dials and Reduction Drives

Filed under: Amateur Radio,Ham Radio,QRP — AA7EE @ 9:19 am
Tags: ,

There are a few things I’ve been wanting to write about here. A couple of fellow builders have regen builds that I’m keen to relate. I have also wound two more coils for The Sproutie and would like to pass the details on, as well as a few thoughts on the subject, and coil-winding tips. However, I am experiencing a certain malaise toward writing at the moment, so will take the easy way out for the time being and simply post pictures of some vintage parts I recently acquired.

Like most builders, I like to keep a stash of parts that my be needed for upcoming projects. I don’t buy indiscriminately though – a part needs to have a good chance of being used for me to consider taking it on board. During my career as a DJ and voiceover guy, I collected CD’s fairly indiscriminately over the course of a couple of decades and ended up with a large collection that has taken a great deal of time and effort to slowly reduce in size. I don’t want to do the same thing with radio parts. However, given that I think I still have a regen or two left to build, there are a certain number of quality variable capacitors, reduction drives, and dials that still need to be given a good home in my shack 🙂

I get many of my vintage parts from eBay. I am quite picky about condition, and also reasonably disciplined when it comes to price.  There’s a Hammarlund MC-100-M variable capacitor on eBay right now. It’s used, in good condition, and it has a “Buy It Now” price of $60. There is no way I would pay that much for such a part. I have bought similar units in very good used, and NOS (new old stock) condition for $15-$20 in the last year from eBay. I consider $15 for a part like this to be a good deal, but 4 times that is exorbitant. I imagine the seller is thinking that he will sit back and keep it listed until someone buys it. Perhaps someone will.

This week, 3 really good parts arrived in my mailbox, all manufactured by the National Radio Company. The first 2 were knobs and skirts, fitted with 5:1 “Velvet Vernier” reduction drives. These planetary friction drives operate smoothly, and look good too. The first one came in a really cool box. It’s in fantastic (unused) condition and was still in it’s box –

A view from the rear –

The big manufacturers such as National, Hammarlund, EF Johnson, must have produced huge numbers of their parts, yet it still boggles my mind that there still seem to be quite a few sitting around in NOS condition, never having been used before. It is a thrill to incorporate these parts into a new project, and is one of the factors that drives me to carefully plan anything before building it. I want these remaining parts to be used in something worthwhile.

The other knob and Velvet Vernier drive was even more impressive. It was so clean, bright and shiny, my friend commented that it could have been manufactured yesterday. I agreed. It really looks that good –

The reduction drive looks like it is made from stainless steel, which contributes to it’s shiny, new look. It even came with 4 original stainless steel mounting screws, in perfect condition, one of which has a pointer head for placing at the very top of the numbered skirt.

Here’s the same part from the back. I was gobsmacked when looking at this for the first time. It could indeed have been made yesterday –

A couple of days later, another knob and drive I have been wanting for a while arrived. As a teenager, a local ham gifted me several large boxes full of tubes, chassis, and assorted parts. Among them was the famous National HRO dial, coupled with an NPW-0 gear drive. The NPW-0 was the one in which the shaft that was coupled to the variable capacitor was perpendicular to the front panel.  I’d spent plenty of time as a teen admiring that dial and gear drive, but I lacked the skills and tenacity to incorporate it into a project and to this day, I don’t really remember what happened to it. My parents probably committed much of my parts stash to the trash after I’d been in the US for a few years and they’d figured that I most likely wasn’t coming back for it.

The unit that arrived in the mail a couple of days ago was the famous HRO dial, this time coupled with a gear drive that has an output shaft parallel to the front panel.  I wanted one of these because the internal mechanism is much simpler, consisting of just a split gear and a worm drive (the other type uses six gears). A nice variable capacitor came with it, which measured at ~15-245pF. It will make a good, accurate band-setting capacitor. I am not yet sure how easy it would be to use this drive with a different variable capacitor, or if I am “stuck” with the one attached to the unit, but using the attached one will simplify the physical construction of a receiver somewhat –

The vague plan right now is for this HRO dial and drive to end up in a regen (what else!) I was even thinking of having two identical ones – one for accurate bandsetting, and one for the bandspread, though that might be overkill. I have been doing some thinking as to what, if anything, my next regen should be. I haven’t built many regens and don’t think I will become one of those enthusiasts who builds many dozens of them. I don’t have a lot of regens to compare The Sproutie with, but I don’t think that regen performance gets much better, with the possible exception of the circuits that are at the very cutting edge of modern regen research (yes, there is such a thing). The Sproutie is fantastic for AM SW listening, being both sensitive and stable, with a regeneration control that slides smoothly into oscillation. SSB reception is a little trickier but from what I’ve been reading, it shares this in common with most (if not all) regens. I’m curious about tube regens but have doubts as to whether even a good tube regen would have better performance than a well-designed and constructed solid state one. NOTE – If anyone has experience or thoughts on this subject, I would very much like to hear them.

So I’m rather stuck, as I think that with The Sproutie, I may have stumbled upon a regen architecture and circuit that works particularly well and is convenient to use. The coils are easy to wind, as there is no separate tickler tap/winding, and the regeneration is smooth. This exact same circuit was used in the WBR. The WBR achieved it’s high oscillator/antenna isolation through the use of a balanced tank circuit. The Sproutie achieves it through the use of an RF stage, so there are no problems with common mode hum, a malady often experienced with designs that don’t employ an RF stage. You won’t experience issues with microphony either, if you build it sturdily (that part is up to you!) I can’t see why I should even experiment with other circuits, unless they are likely to offer a substantial improvement.  Circuit-wise, the only thing I’d quite like is a bit more audio power, so that I can really pump audio into a separate speaker for those occasions when receiving a strong and quality signal.

These are the features I’d like for my next regen (if it ever gets built) –

1) One or two National HRO Dials and drives

2) A bit more audio power for driving a decent external speaker to room-shaking volume

That’s it really. My Sproutie is that good. I am looking for an excuse to use this beautiful HRO dial in another regen, and cannot think of any substantial circuit improvements. Sure, I could build a tube regen but if it’s not going to perform any better, what’s the point? I know they glow, and that alone is cool, but I need a little more of a reason than that.

Thank you for letting me think aloud, and share some gratuitous pictures of my new vintage parts acquisitions.





January 12, 2015

A Crowdfunded Si5351 Breakout Board From Jason NT7S

Followers of Jason NT7S’ blog “Ripples In The Ether” will know that he has been experimenting with the Si5351 chip.  This little $1.50 (or cheaper) device is a PLL clock generator which provides 3 independently programmable outputs from 8KHz to 160MHz. While it’s phase noise is not quite as good as the Si570 (the chip used as the frequency-determining element in the Elecraft KX3), it’s a whole lot cheaper, and indications are that it’s performance will be easily good enough  for many rigs. There was some talk over on the Minima mailing list about using it in a version of Farhan’s new open-source transceiver project, The Minima.  At less than $1.50 for the device, you can imagine how useful this could be as the frequency determining element in a whole new generation of QRP rigs.

Jason talks about it at length on his blog at http://nt7s.com/

Enter the Etherkit Si5351 breakout board –

An earlier version of the Etherkit Si5351 breakout board. The crowd-funded version will omit the broadband output transformers T1, T2 and T3 in order to keep costs down. (Photo courtesy of NT7S)


To make experimenting with this chip even more tempting, Jason is crowd-funding a run of these Etherkit Si5351 breakout boards. More details here. As this blog-post goes to press, the Indiegogo campaign, which was launched earlier today (Sunday) has already reached it’s minimum goal for funding. It runs until Feb 10th. Show your support for Etherkit!

Join Jason’s Indiegogo campaign here!

January 7, 2015

Does The Sproutie Regen “Work” On SSB and CW?

Since building The Sproutie a few months ago I have had a great deal of fun with it. It is only the 4th regen I have ever built, but it is the best one so far. One of my main motivations for building it was to own a “serious” regen. I have long thought that the main reason this type of receiver is not taken more seriously nowadays is because they are rarely taken seriously when being built – and perhaps even designed. Kit designers are forced to make severe compromises because, well, who is going to pay hundreds of dollars for a high quality regen kit? A few of us would, but probably not in large enough numbers to make such a kit economically viable.

As an example of taking things seriously when building a regen, take a look at this build of NR5Q’s “Ultimate Regen” by Jim K4XAF.  Now that is a receiver any avid SWL would be proud to own and operate.

To make a long story short, I wanted to prove to myself that a regen could serve as a useful and valuable listening tool.  I was mainly concerned with SW AM broadcast stations as my main station rig, a K2, doesn’t have general coverage receive. For AM shortwave listening, The Sproutie is indeed very usable, and definitely more than just a novelty. I had spent very little time or effort listening to SSB and CW, and my initial impressions were that CW reception was fine, but SSB reception was occasionally good and occasionally not. I didn’t really think about why, and thought that perhaps it was something to do with the design that I didn’t understand.

Recently, I spent some time with The Sproutie on the ham bands, and the obvious finally occurred to me. It works fine on SSB but when the input signal is too strong, the oscillator pulls, resulting in FM’ing of the signal. In order to overcome this, the best way to operate The Sproutie when listening to SSB is to run the AF gain at, or near, maximum volume, and use the RF gain to set the desired volume. This will ensure that on strong signals, the RF gain is kept down. This is counter-intuitive to anyone who is used to operating a modern receiver with a product detector, where the modus operandi is usually to keep the RF gain at, or close to max, while using the AF gain to control the volume. However, if you got your start with SSB by using an older receiver that had a diode detector and was primarily designed for AM, you’ll remember that controlling the amount of BFO injection was fairly important in resolving the SSB signals well. With one of my first radios, a British R-107 WW2-era military receiver, I was taught to keep the AF gain turned up, and to control the signal-to-BFO ratio by adjusting the RF gain. On strong signals, I quickly learned to keep the RF gain down so there wasn’t too much input signal for the amount of BFO signal. With The Sproutie, the principle is the same, except you are also limiting the amount of input signal so as to not cause the oscillator to pull. Those who have built and operated a number of different regens will be able to comment on this, but my sense is that this is a very common issue with them. Perhaps some designs minimize the effect of oscillator pulling. Can anyone more experienced than me comment? (Note – qrpgaiijin did. Please see his comments below this post on the reasons for oscillator pulling in regens. Input from experienced builders is very valuable so if you’re interested, please do take the time to read.)

Also note that another technique you can use to prevent oscillator pulling on stronger signals is to increase the amount of regeneration. On weaker signals, you might want to reduce the amount of regeneration closer to the “critical” point of onset of oscillation.  At that point, sensitivity is greater, which will help with the weaker signals. Of course, all these adjustments will affect the tuning, so you will need to adjust for that. It’s all part of the fun of operating a regen!

To sum up, The Sproutie does indeed resolve SSB signals well, but it requires much more attention and input from the user than other receiver architectures do. The “sports car with a stick shift” analogy works well here. When tuning the bands for SSB signals, you need your hands on the controls on a much more regular basis than when tuning AM signals. Listening to a QSO with stations of vastly different signal strengths can be an exercise in user attentivity and engagement.

By contrast, listening to AM stations on this receiver is much easier. If the oscillator pulls a few 10’s of Hz on strong AM signals (which it almost certainly does), you’re not going to hear the effects. It’s still a good idea to run the AF at a high gain setting so as not to overload the detector, but the need for this is nowhere near as critical. In fact, listening to AM stations on this little gem isn’t much more work than doing the same thing on a superhet. Although the precise regeneration point varies with frequency, you don’t need absolute maximum sensitivity when scanning the band for signals. When casually tuning a SW BC band, I can tune several hundred KHz before roughly resetting the regeneration control. Only when I find a signal I want to investigate further do I take the time to set the regeneration more precisely.  It’s a process that becomes second nature after a while. I can almost imagine the diehard regen users in the 1930’s deriding owners of the newer superhets, as they were too easy to use and “not real radios”. What’s the betting that happened?

So here’s the deal – The Sproutie does indeed receive SSB just fine, but you’re going to have to put a bit of work into it. It is, after all, a sports car with a stick shift, and not a luxury sedan with an automatic transmission:-)

NOTE – I just read the original article in Electric Radio magazine, describing NR5Q’s “Ultimate Regen”. There is, of course, no definitive word on whether it is indeed the best regen out there, but I took heart from the following quote by Bruce,

“Before we go any further, if you are a SSB operator you may be wasting valuable time. While I listen to SSB all the time on my ‘regens’ I would not want to try to operate a SSB station using nothing but a homebrew regenerative radio – that would be an exercise in futility.”

The above quote comes from a gentleman who built over 60 regens and authored many articles in the pages of Electric Radio. His words mirror my experience with The Sproutie, and further cements my belief that, as far as regens go, this one is pretty darned good. I love listening to AM on it, really like listening to CW on it, and although I can listen to SSB on it with little difficulty, I’d rather listen to SSB on a superhet with a product detector.

Apologies if you’re viewing this on a low-resolution screen, but I have an affinity for nice large pictures of radio sets.

January 6, 2015

7.28MHz Ceramic Resonators Arrived – Test Results

About a week ago, Joel KB6QVI, tipped me off to the fact that Cecil K5NWA was selling 7.28MHz ceramic resonators on his online site, The Parts Place. Enthused, we both ordered some, and both our orders arrived yesterday. Joel slipped his into a test circuit, which gave him coverage of 7.015 – 7.236MHz. He used a similar circuit to the one I used, though I don’t know his exact component values. Here’s the test circuit I used, which gave me a coverage of 7.080 – 7.268MHz –

Test circuit for the ceramic resonator. The transistor can be any low signal NPN type, such as a 2N2222, 2N3904 etc.


Adjusting the values of the 470p and 270p capacitors to, say, 330 and 270, or both to 330, should give a higher maximum frequency.  If I were using this in a simple rig, such as a Micro 40, Beach 40, or similar, I’d be using varactor tuning.  The 1N4001 (the “poor man’s varactor”) can have a minimum capacitance of as little as 5pF with an 8V bias across it, which would help too. It looks like it could be a useful component for simple 40M phone rigs and with a bit of experimentation, I bet I could increase the maximum frequency and get it close to the top of the US 40M band at 7.3MHz.  If you’re in a part of the world in which your 40M band ends at 7.2MHz, then some extra parallel capacitance should do the trick. It’s a 3-pin resonator. If the center pin is grounded, then the internal capacitors are placed in parallel with the resonator. Ignoring the center pin and connecting to the 2 outside pins only, leaves the internal capacitors out of circuit, increasing the maximum frequency.

If you have any interest at all, it wouldn’t hurt to stock up on a few. Resonators for frequencies like 3.58MHz seem to always be in plentiful supply, but ones with frequencies that are useful for the phone portion of 40M are harder to come by. Who knows how long these will be available for?

PS – as I mentioned in the previous post on this subject, these resonators are also available from Mouser, both in the US and the UK. Thanks to Steve G1KQH, for the tip. Here’s the link to them on Mouser’s site. If you set the site to the country you are in, then the link will show you the resonator on the Mouser site specific to your location.


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