NOTE – Many thanks to Aaron N9SKN and Cliff WA9YXG, who pointed out errors in the schematics. They have been corrected. N9SKN, and several others, have built working Sprouties from the schematics in this post so rest assured that if you follow them, you can too.
If you’re thinking about building this great little general coverage regen, I’d urge you not to print out any of this article to work from. The reason is that whenever I make an improvement or addition to this receiver, I edit this article. By working from a printout, you’ll be missing out on any changes I subsequently make. Having said that, The Sproutie works fine as is, so don’t be scared off from building it.
I’ve mentioned before in posts how one of my first shortwave receivers as a teenager growing up in England (in fact, possibly the first) was a one tube battery-operated regen built from a kit. Many of the popular electronics magazines at the time, including my favorite, Practical Wireless, carried advertisements from a company called H.A.C. (“Hear All Continents”) who sold kits for simple HF regenerative receivers. This was the ad I remember best. To the teenage me, this receiver was the holy grail. With this receiver, there would be no stopping me. I would be the king of the hill, if only I could have this magnificent shortwave receiver –
I saved my pennies and eventually sent off for the H.A.C. Model DX Mk. 2. It wasn’t as fancy-looking as the one picitured in the ad, as it didn’t have a front panel or a calibrated dial but hey – those kinds of regens were only for the truly well-heeled, and I was just a kid with a modest allowance. The kit that arrived used an HL23DD valve (or equivalent). It was a battery operated double diode triode, with a coated filament, to maximize emission on the low filament voltage of just 1.5V (2V maximum, with a current consumption of just 50mA). This set didn’t have a front panel or a calibrated dial, sporting just a modestly-sized aluminum chassis with 3 chicken head knobs on the front, but with my 2000 ohm headset and 90V high tension battery, I truly was the king of the shortwave hill. I don’t have any pictures of my H.A.C. Model DX Mk. 2, but featured here are pictures of someone else’s taken from Louis Muelstee’s great website, which is where the ad shown above came from too.
Truth be told, this wasn’t exactly the most sensitive receiver ever created, but it mattered little to a teenager in England in the 1970’s, with plenty of loud shortwave broadcast signals. There was much to keep those high impedance headphones firmly glued to my head. They were fairly cheap quality, and the way the metal headband tensioned the earpieces against my ears made them a little red after 30 minutes of use. Did I care? Not at all – I wore them for hours on end, as I was enthralled by the sounds of Radio Nederland, Radio Prague, Radio Tirana Albania, Radio Moscow, The BBC World Service and many other broadcasters, as well as all the weird-sounding utility stations and the very mysterious numbers station from East Germany. I had no idea back then what it was, but the female voice announcing strings of numbers in German was strangely compelling. Every day, I would rush home from school, eager to get into my bedroom, plug the low-tension battery in, wait for a short while for the tube filament to heat up, then connect the high tension battery and clamp the headphones to my head, cup of tea by my side, as another listening session began. Weekends were heaven. As soon as all my homework was out of the way, there was nothing but blissful hours and hours of potential shortwave listening time stretching ahead. From time to time, the 90V battery would run down, and I would walk the 2 miles into the village of Astwood Bank to buy a new one from the local gas station. It didn’t take me long to figure out how to power the filament from a transformer in order to save money on low tension batteries. I eventually figured out how to do the same for the high tension supply too. On good days, I could even pick up some local amateurs on 80M SSB. Man, I was indeed the king of the shortwave hill! At the back of my mind, though, was the idea that somewhere out there was still a truly dreamy shortwave receiver – one that had a front panel fashioned from a sheet of aluminum, and a calibrated tuning dial. It only took me until the age of 50 to finally own one of those only-in-your-dreams kind of receivers.
Which is what this blog-post is all about.
I’ve had some encouraging success with regens recently. Both the WBR and my modified version of the the WBR, which I built for the 31M BC band, worked well, with no common-mode hum, instability, or any of the other kinds of naughtiness that sometimes accompany the operation of regenerative receivers. There was one main thing about the WBR’s that limited them for me, and that was the fact that they only operated on a limited range of frequencies. After building these 2 receivers, the next logical step was to build a general coverage regen with plug-in coils. I wanted a set that was built solidly, with a reduction drive and a calibrated tuning scale, so that I could prove to myself something that I already knew – that a regen, properly constructed, can serve well as a shortwave receiver rather than just as a novelty, which seems to be the category most people have placed them into these days. I’m reminded of a comment on a discussion forum I saw recently, in which a gentleman was talking about a regen he had built once. It was sensitive, received lots of stations, and gave him much enjoyment, he said, but he never really knew where he was on the band. “Well of course you didn’t!” I thought to myself, “but that’s not because it’s a regen – its because when you built it, you didn’t build it with a calibrated dial. It’s not the regen’s fault you didn’t know where you were on the band – it’s yours!”
Charles Kitchin had a design for a receiver which caught my attention. It was published in the Feb 2010 edition of CQ Magazine and consisted of an oscillating detector feeding a 2-stage amplifier consisting of a low-noise FET-input opamp acting as the preamp. The preamp had a low-pass filter with a variable cut-off point, as well as an extra capacitor in the audio chain that could be switched in to give a nice lift to the lower frequencies, for those times when you have a nice strong signal and want a bit of bass boost. This preamp drives an LM380, which makes for a much lower noise AF amp chain than the default in these types of receivers that employ an LM386. On top of that, there is provision for a line out jack for recording. I was interested – regardless of the front end I used, this could definitely be the AF amp for a “serious” regen!
Before I had even fully decided on the finer details of this project, I assembled the AF amp on a separate board. I wanted this to be a somewhat modular receiver, with the AF and RF sections built on different boards so that if either section didn’t work out, I could try a different one. I wasn’t entirely convinced that the value of Hammarlund tuning capacitor that I was planning on using was going to be ideal, so I wanted it to be a relatively easily swappable part with other tuning capacitors of different value but with the same form factor (of which I own a few). If I was going to go to the trouble of building something like this on a nice chassis, I wanted to give myself the maximum possible chance of succeeding.
Here is the schematic of the AF board. It is a little different from the version originally designed by Mr Kitchin (though not by much) as I will explain –
In Chuck’s original version, the 2.2K resistor on the input was 5K. The ratio of this value to the value of the 100K resistor between pins 2 and 6 of the AD820AN determine the gain of the stage, and I wanted a bit more. Also, the LM380 was motorboating when the AF gain pot was set to anything higher than half-volume, so I added the 10 ohm resistor in the supply line and bypassed it with a 470uF electrolytic, which stabilized it nicely. The +ve supply line was connected directly to pin 7 of the AD820AN, but this could also be bypassed if necessary. A series 100 ohm resistor with a 47uF or 100uF bypassing to ground should work nicely. You can also sprinkle a few large decoupling electrolytics in the range of 100 – 470uF at various points on the 12V bus directly to ground. A small issue I experienced was that when the AF gain pot was at absolute maximum volume, rotating the low-pass filter pot caused clicks and “bloops” in the speaker. It seemed to only happen when the slider of the pot had finished traveling over the carbon track and had actually made contact with the metal that formed the hot end of the control. A 47 ohm resistor placed at the hot end of the 10K AF gain pot provided the necessary isolation (this is shown in the schematic). I was left with a volume control that operated smoothly, and a variable low-pass filter pot that also operated smoothly. I also added a 0.1uF coupling capacitor on the input (pin 2) of the LM380. The 0.1 and 220uF bypass capacitors on the 12V line were placed so as to bypass the 12V supply directly at the point of entry into the chassis. They were soldered directly on the back of the DC power connector and grounded with a solder tag bolted to the chassis. The 1N4001 diode was also placed at the same point.
Here’s the AF board as I first built it, before changing the 5K resistor on the input to a 2.2K resistor – and before adding the 10 ohm resistor in the 12V supply line and the 470uF capacitor to bypass it. The lengths of lavalier mic cable for the variable low-pass filter and the AF gain potentiometers have already been soldered in place, and they exit through holes drilled in the board. The headphone jack and DC power connector are temporary, for the purpose of testing. The Manhattan pads are of course, as always, W1REX’s MeSQUARES and MePADS –
The front end is a very standard design. It is the same configuration (and indeed the same circuit) as used in the WBR, with the exception that the tank (unlike that in the WBR) is unbalanced. This same arrangement was used in Nicky’s TRF, as featured in issue 70 of SPRAT, and I believe the original circuit was developed by GI3XZM. I wanted this receiver to be usable over a wide range of frequencies, and in keeping with my “modular” approach, wanted the receiver to be as versatile as possible. A plug-in coil system, with both gangs of a dual gang variable capacitor, as well as the fine tuning capacitor, all available at the pins of the coil base, allows for a lot of flexibility when winding coils for different bands. The user decides, when constructing a plug-in coil, whether to include parallel or series capacitors for the main tuning and fine tuning capacitors, as well as choosing whether to use one, or both gangs of the tuning capacitor. In this way, with some calculations and a bit of trial and error you could, say, wind a coil to cover a large segment of the HF spectrum, or a single narrow band of frequencies. If, after some listening, I decide one day that I am particularly interested in the 16M broadcast band, I can construct a coil to cover just that one band. Neat!
The J310’s in the RF amp and the detector stage could be any similar N-channel JFET such as the MPF102 or the 2N3819. Likewise, the two 2N3904’s could be most any small signal general purpose NPN transistor. I originally fed the output of the J310 “infinite impedance” detector stage directly into the input of the AF amp board, but quickly discovered that the gain wasn’t enough to comfortably drive a loudspeaker. Had I done a few quick calculations beforehand, I would have realized that. I wanted to take advantage of the fact that the output chip is an LM380, by driving it enough to make a loud noise into the speaker! Adding the single 2N3904 preamp stage after the detector solved the problem nicely. I have built enough of these simple receivers that can drive “a small speaker to a comfortable volume in a quiet room” 🙂 No more!
As with any circuit of this type, the RF stages, and the frequency-determining part of the circuit especially, should be built with short leads, and stiff wiring. Top quality components will help. The two 330pF capacitors in the feedback circuit of the 2N3904 oscillator stage should be NPO’s (or C0G’s – same thing), as should the 39pF capacitor. The coils were wound on toroids, and the coil assemblies mounted in octal tube bases. I spent a great deal of time on W8DIZ’ site, using his online calculators to figure out the number of turns required for varying degrees of coverage. Unless you build a receiver with the same variable capacitors, and use a very similar physical layout, you’ll need to do your own calculations, and then be prepared to tweak the final values of inductance and capacitance to get the coverage you want. Incidentally, I used a Hammarlund MCD-35-MX dual gang component for the main tuning capacitor. It was this one that I got a deal on over a year ago. The official specs say that each section has a capacitance of 6 – 31pF, but I also had to make a rough estimate of the stray and circuit capacitance when calculating the required values of inductance and capacitance to cover each band. My fine tuning cap was a Hammarlund MC-20-S, and I had to include the capacitance of that in the calculations too. This is the online calculator on W8DIZ’s site for the T68-6 core. He has similar calculators for all the popular toroids. Very useful stuff. Note – for some reason, the calculator doesn’t always estimate the correct length of wire that needs to be used. This is easy to work around. Just wind one turn around a toroid measure it’s length, multiply that by the number of turns, and add a few extra inches for good luck (and pigtails).
Here’s a view of the RF board as initially built, before adding the extra (pre-AF board) preamp stage –
Here are the details of the coils wound so far, including the temporary “experimental” coil for 24-29MHz. I didn’t get as far as installing a link winding for this coil, but the main coil was picking up plenty of signal from the proximity of pin 7 of the tube socket to the coil. I have been very pleasantly surprised at how sensitive and stable the set is at these higher frequencies. Soon after winding it, I copied SSB on the 12M and 10M amateur bands, as well as plenty of over-modulated and very loud local signals on 27MHz 🙂 Unless you also use the same values of tuning and fine-tuning variable capacitors, and closely copy my layout, your values will be different, but here is the info on my coil set so far. After a little while spent looking at it, it should make sense. Once you get used to figuring out how to wind a coil for a specific set of frequencies, it’s fun. I have 15 coils so far, with ideas for a few more. I have already filled up my cigar box coil box, and am getting ready to make a second coil box and wind a few more coils. One of the really enjoyable things about a regen with plug-in coils is making coils for new bands. Fun!
If you wind too many turns for the link winding, you may find that you have to turn the regeneration control nearly all the way clockwise in order to reach oscillation, or you may not be able to reach it at all, as the link winding loads down the oscillator. It is particularly easy to do this on the higher frequency bands. If this occurs, remove a turn or two from the link winding. In operation, it is easy to overload the detector (as it is with all regenerative receivers). I use my Sproutie with a large outdoor antenna and find that on the lower bands, I usually only need to operate the set with the RF “gain” control set halfway.
The 15855 – 17850khZ coil stops about 50KHz short of the top of the 16M band, which is nominally 17480 – 17900KHz. However, all these coverage figures are quoted with the fine tuning control set to maximum capacitance. With the fine tuning control, I can tune all the way up to 17900KHz with that coil plugged in.
With the first set of coils I wound for specific bands, I was using significant values of fixed capacitance across L1 in order to reduce the frequency swing caused by adjustment of the main tuning capacitor. I noticed after a while that these specific band coils weren’t giving such good sensitivity as the general coverage coils. I have since discovered that it is best to avoid large values of parallel fixed capacitance, as this seems reduce the performance. Adding a capacitor of a few pF to tweak the coverage is fine, but large values (of the order of 50 or 100pF) will reduce performance. If you want to reduce the frequency swing to cover a narrow band, best to achieve it with the use of a capacitor in series with the main tuning capacitor instead. The performance of the coils in this receiver seems to be maximized by using as much inductance and as little capacitance as possible. This is more noticeable on the higher frequency bands.
The table for specific band coils is a work in progress. I will add to it as I wind more coils –
The coils were constructed in two different ways. The lower frequencies used a larger T68-6 core which I mounted with nylon hardware. I first took a #10 nylon bolt, cut the head off, and epoxied it into the hollow center spigot of the tube base thus –
Before adding the toroid, any jumpers and capacitors were soldered in place (this is going to be the 3050- 3950KHz coil). The soldering’s a bit messy, but it was the first time I had soldered one of these things –
A couple of nylon nuts followed, then a nylon washer, and then the toroid, topped off by another washer and finally, another nut –
The higher frequency coils used T50-7 toroids, and were mounted vertically and secured with a couple of dollops of hot glue from a glue gun. In the following picture, the 3050 – 3950KHz coil is on the left, the 14460 – 15980KHz coil in the middle (in a white ceramic tube base), and the 8040 – 10720KHz coil on the right. The middle and right coil were pictured before the hot glue was added. Since building this version of The Sproutie, I have started using hot glue for the larger, lower frequency coils too, and it works fine. It is a lot faster than using the nylon bolts and nuts –
Here’s the 14460 – 15980KHz coil with the 2 dollops of hot glue to secure the toroid. I like these ceramic bases and think I’ll use them for all subsequent coils. Incidentally, here’s a quick hot glue tip. I don’t know what temperature the guns that have a single setting use, but if you purchase a dual-temperature gun and use the dual temperature sticks, the hotter setting allows the the glue to flow more freely before it sets, which makes building these coils a bit easier, and gives a better end result. I think the coils in these photographs may have been made with the temperature inadvertently set to the lower setting, giving me headaches while the glue was setting as to whether it was going to flow into all the places I wanted it to before it set! –
The coils for the higher frequency bands need less in the way of a link winding, such as 1/2 a turn, which is simply a piece of wire passing through the toroid, but not even being wound around it. For the 16M/17M coil, I found that a 1/2 turn from pin 1 to pin 7 wouldn’t allow the circuit to oscillate, so I used a simple u-shaped loop of wire between pins 1 and 7 placed near the toroid, as in the photo below. The link winding is the green wire. My attempt at using a 1/2 turn link winding for this coil involved a wire from pin 7 through the toroid to pin 1, and this stopped oscillation. However, it’s possible that a 1/2 turn from pin 7 directly through the toroid to pin 4, which is also at ground potential, might allow oscillation while coupling more signal into the detector (it’s a shorter run of wire). I didn’t try it though, opting instead to go for a loop outside of the toroid. Experimentation is definitely key here, and it’s one of the things I had in mind when building The Sproutie. Once you’ve built the receiver, you can still have plenty of fun designing coils for many different bands and amounts of coverage. Here’s that 16M/17M coil, showing the green link winding –
When designing coils for The Sproutie, here are a few things to bear in mind –
Adding capacitance across the coil will bring the overall frequency down, and limit the range of frequencies that the main tuning capacitor will cover (as the tuning capacitor is now just part of the overall capacitance across the coil). However, if you place too much capacitance across the coil, the circuit will not oscillate. When making estimates and performing calculations, remember to include the capacitance introduced by the circuit, and stray capacitances. Another strategy for limiting the range of frequencies the tuning capacitor covers is to put a capacitor in series with it (the tuning capacitor). If I haven’t already mentioned it, the online calculators on W8DIZ’s site are great for figuring out resonant frequencies for tuned circuits involving toroids. The calculator for the T50-7 is here, and the menu to the left of the page has links for the pages for each of the other toroid cores. Each page also tells you what range of frequencies that particular material is good for. However, even after you think you’ve figured out what values you need for the inductor and capacitors, whether you’re going to use padders, series caps etc, you’ll most likely still have to do some tweaking of values until you get the coverage for each coil that you want, based on observation and experimentation. Once you’ve got the exact values you want, make sure to hot-glue the toroid to the tube base. If you don’t do that, you’ll experience instability and microphony. It’s amazing what difference a couple of dollops of hot glue will make!
For the chassis, I first looked at what was available in off-the-shelf sizes and couldn’t find anything that fitted the bill. Hammond have a good selection of different sizes, but their enclosures, for the most part, use 0.04″ thick aluminum. I wanted something thicker, for a very sturdy structure, so I decided to look into having a custom chassis made. A bit of searching turned up two businesses that manufacture aluminum chassis’ for homebrew tube amp enthusiasts – Dirty Dawg Amps, a US based business who are temporarily out of business due to a fire, and Seaside Chassis Design, who are located in Novia Scotia. Seaside Chassis use a minimum of 14 gauge aluminum for their enclosures. 14 gauge is about 0.064″, which I knew would make for a nice stout case.
Terry was very communicative and straightforward via e-mail about what he could do and what it would cost. I sent him rough drawings, with dimensions, of the chassis, front panel, and mounting bracket for the main variable capacitor that I was hoping he would be able to fabricate. He was able to make all 3 items and on top of that, he would punch all the main holes for me, leaving me just to drill the smaller holes for mounting screws. This was great news, knowing that I would shortly have a solid and well-made chassis on which to build this receiver.
I dropped the ball somewhat and didn’t take a picture of the chassis when it arrived, but here’s what it looked like with all the main components fitted, before wiring it all up. The 2 biggest factors in making this receiver look so grand are the National “N” dial with Velvet Vernier drive, and the excellent chassis. Does this look inspiring or what?
The controls on the upper row are, from left to right – regeneration, the main tuning knob, and the fine tuning. On the lower row, also from left to right is the headphone socket, RF attenuation, the bass boost switch (down = more bass) , the low-pass filter cut-off control, and the AF gain control.
Here’s a view from the back at this point in the construction. Look at that accurately made chassis, front panel, and capacitor mounting bracket. Terry from Seaside Chassis Design did a great job –
Both the RF board (without the extra AF preamp that was built later) and the AF boards installed but not yet wired up. All cables are tagged for easy identification –
Another view of the underside, before everything has been wired up –
The next task was to begin wiring the boards to each other and to the controls. Looking at this view of the underside, I’m thinking that I perhaps could have put a little more effort into dressing the cables more neatly, but it’s perfectly functional. The schematic shows pin 1 of the octal base being grounded but as I was wiring it up, I decided to also ground pin 4 –
Some more views of the underside from different angles and distances. I only twisted the 12V supply lines together for neatness and not for any electrical reason, though it does rather make them look like tube filament wiring 🙂 Just to the left of the antenna socket on the right, is the phono jack for the line out. This is such a useful feature. In fact, as I write this, I am using the line out to record KCBS from Pyongyang on 11680KHz. On the other side from the BNC antenna connector, you can see the DC power jack with the reverse polarity protection diode and the RF bypass capacitors. Vinyl grommets were used for all wiring that needed to pass through the chassis. RG-174/U in the form of Belden 8216 was used for the connection from the BNC antenna connector to the board, and lavalier mic cable with 2 conductors and a shield for all other connections to controls (and to the phono jack) –
A view from the top, with a coil plugged into the octal tube base. The shaft couplers came from different sources. The one on the left, on the main tuning control, is a Jackson Bros part, purchased from Mainline Electronics in the UK through eBay. The coupler on the right was made from all aluminum by John Farnsworth KW2N. He has a small business making these and can also make custom sizes, if you have a non-standard shaft you want to use. For instance he just made a 3/16″ to 1/4″ coupler for my next project. John sells on eBay, but you can also contact him directly through his fledgling website (not yet finished) here. I really like his all-aluminum couplers –
The original intent was to mount the internal speaker on top of the chassis on the side using some kind of simple right angle bracket(s). I didn’t ask Terry from Seaside Chassis to fabricate a bracket for me because at that point, I didn’t know what speaker I was going to use. Looking around my room for something I could use, I noticed an unused LMB Heeger enclosure #143 in the size 4″ x 4″ x 2″ – exactly the same enclosure I used for the 31M version of the WBR. I figured that the top part of the box, being a U-shape, could be used as a bracket. If using that part though, why not use the whole box? There might even be some extra acoustic benefits to housing the speaker in a little case, and having it fully enclosed will protect it from dust and small bits of wire, metal filings etc being attracted to the speaker magnet (which happens here in the shack). The sound was a little “boomy” with the case closed, so I stuffed some foam in with the speaker, and it cleaned the “boominess” right up. Although you can’t really see it in these next shots, the speaker case is bolted to, and spaced off the chassis with 4 vinyl grommets to dampen any unwanted acoustic resonances in the chassis. The speaker wire enters the speaker enclosure through a grommet in the side. It’s a small detail, but the grommet is mounted not in a hole, but in a slot in the side of the cover. That way, when I remove the cover of the speaker enclosure, I can slide the grommet out, leaving the grommet still on the speaker wire, and allowing me to completely remove the cover –
There are a few improvements and modifications I’m considering making to The Sproutie but it is now completely functional, and this is how it looks at this point. I must say that I think it’s looking pretty good –
I was lucky enough to obtain a National “N” Dial in good condition and nice working order – not all of them look or operate this well. I bought several from Gary at Play Things Of Past and used the nicest one. The tuning knob and reduction drive are an important part of the feel of any receiver, and can do a lot to affect the operating experience so I’ll say a few words on that subject if I may. Before, I do, here’s a clip from a page of the 1947 National Radio catalog. I get a kick from seeing vintage parts in old catalogs, then seeing the exact same thing, in really nice condition, in front of me. It’s a bit like meeting a celebrity for the first time 🙂
I was initially concerned that the 5:1 reduction ratio of the National drive wasn’t going to be high enough for accurate tuning on the HF bands – it was a good part of the reason why I chose the value of the main tuning capacitor and wound the coils so as to limit the tuning ranges to around 2MHz or less. This approach results in more coils, but really helps in creating a regen that can be set to a particular frequency, and from which you can read the frequency (with the help of a calibration graph – more on that later.) This receiver can be set to within a few KHz of any frequency. This is good enough for finding a particular SW AM broadcast station. I can also read the dial setting and then consult my custom calibration graph to find what frequency I am on to within a few KHz. It’s not much by modern standards, but is pretty good for a regen with an analog dial.
The National “N” Dial is marked from 0 to 100 and thanks to the vernier scale located at the top, it can be read to one-tenth of a point. These dials, when in good condition, have a firm yet smooth action with no backlash that makes tuning a receiver like this a good experience. Another thing to note is that these dials were manufactured with CW (clockwise) and CCW (counter-clockwise) characteristics, meaning that as you rotate the dial clockwise, the numbers either go up (CW type) or down (CCW type). This makes sense when you consider that variable capacitors were made as units that either increased in capacity as you rotated the spindle clockwise, meaning that the frequency went down (CCW type), or as units that decreased in capacity as the spindle was rotated clockwise, meaning that the frequency went up (CW type). The latter type is the convention for variable capacitors today. When we rotate our tuning knobs clockwise, we expect the frequency to increase. Back in the days when our predecessors thought more in terms of wavelength, they would have expected wavelength (instead of frequency) to go up with a clockwise rotation of the knob. This particular regen uses a CCW-type variable capacitor, so I married it up with a CCW-type vernier dial. It does take a while to get used to the fact that the frequency goes down when you turn the tuning knob clockwise, but I am beginning to adjust. There seem to be quite a lot of these lovely old National “N” dials around, if you take the time to look. A fellow homebrewer told me that his local electronics surplus store had a number of them in good condition for a very good price (I believe he bought them all!) Hamfests and swapmeets are also a good place to look. eBay is another possibility but the prices asked are a bit on the high side, in my opinion. I got mine from Gary at Play Things Of Past. He was easy to deal with.
Note – the National N dials have 3 small rubber/fiber bumpers installed on the mounting plate to prevent the front metal “flange” (the part with the engraved dial markings) scraping on it when the dial is turned. If your dial is in good condition, none of the main parts are bent, and everything is running “true”, you can remove these bumpers. I did, and the result was a dial that rotated very smoothly. With the bumpers in place, there is a very slight scraping sound as the dial is turned. If you do this, make sure to save the bumpers in case you later wish to re-install them.
One downside to each coil only covering a relatively small part of the shortwave spectrum is that you end up with quite a few of them – more if you decide to wind specialty coils for specific bands. A coil box was definitely in order, so I headed to my local cigar and tobacco shop and purchased an empty cigar box. A trip to the local craft store yielded a length of bass wood, which is a little harder than balsa but can still be cut with a sharp craft knife. I cut slots in the lengths of basswood so they would slot together to form dividers to store the coils in –
The dividers installed in the cigar box, with the coils that had been wound so far (at time of writing this, I now have one more, for the 120M BC band) –
In order to know where you are on the band, you’ll need to calibrate your dial. I accomplished this by plotting a graph for each coil with frequency on the x axis and dial markings from 0 to 100 on the y axis. For frequency references, you can use a crystal-controlled marker, or off-air signals and an online frequency database such as short-wave.info Bear in mind that the setting of the regeneration control does alter the received frequency. Probably the best way to standardize your results is to keep the regeneration at or just below the point of oscillation at each dial setting that you take a measurement. The following is one of the graphs I am currently plotting. The original was larger and it is a little hard to read the markings on each axis on this smaller version. That’s fine, as your calibration will be different anyway. In this graph, look at the line formed by the red dots (the black dots are something different – you can ignore them) –
The variable capacitor I used is what Hammarlund called a “midline” type in which the moving plates (the rotor) were mounted off-center so that the relationship between degrees of rotation and the resulting capacitance was non-linear. The intent was to keep the relationship between degrees of rotation and frequency fairly linear and by looking at the graph, you can see that it is not bad at all. I also found that once a graph was plotted, I was able to set the dial and return to a particular frequency with a good degree of accuracy and repeatability. When listening to AM stations with this receiver and it’s bandwidth, which is of the order of 10KHz, you can be assured of returning to a dial setting and hearing the station you want.
The Sproutie does work on SSB and CW, but SSB reception is trickier due to the need to control the signal input level (with the RF attenuation/gain pot) in order to prevent overloading of the regen detector and pulling of the oscillator, and to adjust the level of regeneration in order to inject the right amount of carrier. If the signal level to the regen stage is too high, the oscillator will pull, resulting in the signal sounding “wobbly” due to FM’ing of the oscillator. This happens very easily, even with moderately strong signals. My preferred method of operating the set when listening to SSB stations is to run the AF gain at, or close to, maximum volume, and to keep the RF “gain” low. Sometimes, I need to keep the RF gain twisted almost to zero in order to achieve a nice stable demodulated signal. When adjusted properly, SSB sounds good on The Sproutie, but it takes a fair bit more work than with a superhet fitted with a product detector. Hams and shortwave listeners who have used older superhets that used BFO injection into a receiver with a diode detector will be familiar with the technique of keeping the AF gain up high, and using the RF gain to control the signal-to-carrier injection ratio. In this case, we are also using the RF gain to prevent the detector from being overloaded and pulling the oscillator. Sound tricky? If you’ve never done it before, it can take time to get used to, but after a while, it becomes almost second nature.
While I’m on the subject of fine tuning, allow me to expound a little more on reduction drives. In contrast to the friction drive on the National “N” Dial I used for the main tuning, the reduction drive on my fine tuning is a Jackson Bros 10:1 ball drive which has a small amount of backlash and feels a bit “spongy”. I don’t like it, and am grateful that for my main intended use of listening to AM stations, I won’t need it. I may change this ball drive for either another friction drive, or a different ball drive. The Xtal Set Society sell 6:1 ball drives manufactured (I believe) by Oren Elliot) that have a more pleasing feel. EDIT – I have since found that making the 2 screws that hold this mini ball-drive to the front panel very, very tight seems to eliminate the backlash and reduce the spongy feel a bit. I suppose it increases the pressure on the bearings a little. For the time being, I’ll keep this drive but if I ever change the front panel, that will be the point at which I’ll drill a bigger hole for a more conventionally-sized reduction drive.
For the above reasons, if I were intending to listen to more SSB and CW on this receiver, I would definitely wind coils to spread each entire amateur band over the whole rotation of the dial, and make sure I had a reduction drive for the fine tuning with very little or zero backlash and a better feel (though having said that, the regeneration control works very effectively for fine tuning).
Another thing that has often interested me is the bandwidth of regens. In general, as you approach the point of oscillation, the bandwidth becomes narrower, until it is at it’s narrowest somewhere around that critical point. As you continue to advance the regeneration, the bandwidth broadens out somewhat. I connected the output of a simple noise generator to the antenna socket of The Sproutie, and took screenshots while running Spectrogram, which was being driven from the line out jack of the receiver. All 3 of these screengrabs were taken just marginally below the point of oscillation (the ideal point for receiving AM). The first one was with the low-pass filter adjusted for maximum bandwidth –
Well, it’s obviously not the kind of brick wall shape we might expect from a good crystal or mechanical filter but if you look closely, the passband is about 25dB down at the 5KHz point and 30dB down at the 10KHz point, That’s not too bad for AM reception, though if you wanted to get really serious about it, a passband of around 5 – 6KHz with a much steeper wall would, of course, be more ideal.
Here’s a grab taken with the low-pass filter pot at the median point, which is looking better –
…and better still with the low-pass filter set to the lowest cut-off point –
It is important to remember that these spectrums represent the response of the entire receiver, and not just that of the front end. SSB and CW signals become higher-pitched as you tune away from the center of the signal, but although the audio frequency make-up of an AM signal tuned off-center does change, the whole signal does not become higher-pitched. Therefore, an audio filter will be more effective at rejecting off-frequency signals for SSB and CW signals than for AM. Nevertheless, the adjustable low-pass filter is very good at cutting down much of the high pitched static that can make simple receivers like this quite tiring to listen to for long periods whatever mode is being received. It makes The Sproutie feel like a “grown-up” receiver!
Here’s The Sproutie, with it’s coil box. I would have felt as if I had died and gone to heaven if I’d had this receiver as a teenager. I’m feeling pretty good about it at my current age of 50 🙂
The Sproutie is not completely finished yet (is any homebrew project ever truly finished?) The changes and additions I am considering include –
-Designing a thicker, and custom front panel with Front Panel Express, and making it a little wider than the current one to allow for a pair of instrument handles to be mounted
-Changing the 10:1 Jackson Bros reduction ball drive on the fine tuning control for something with less backlash and a firmer, less “spongy” feel
-Winding more coils for specific bands, so that the bands I am most interested in can be spread out over the entire dial, making tuning using just the main tuning control even easier
-I had also considered finding a local cabinetmaker to make a wooden cabinet for The Sproutie, but am not too sure about the convenience of sliding the chassis out of the cabinet every time I want to change a coil. If you’re thinking about building a receiver like this, completely enclosing it in metal would be quite a good idea – perhaps with a hinged flap or door on top for coil-changing. Regenerative receivers are quite sensitive, and this one picks up signals from my computer and/or my monitor, which are located nearby
It always feels good to build something that works, and The Sproutie certainly does that. It’s a great little receiver for shortwave listening and with an extra tube base, a toroid, some wire and a few extra capacitors, you can add whatever frequency coverage to it you like as you go along.
Oh – and I just realized I didn’t explain that Sproutie is the nickname I gave my 2 1/2 year-old cat Sprout, whose ham radio name is Sprat The QRP Cat. I had already named one of my home-brew radios after a kitty I used to have called Rug, so figured it was time to honor Sproutie in the same way.
Videos of The Sproutie in action are here.
Thoughts on using The Sproutie to receive SSB are here.
I continue to update and re-write this post, as I make additions and improvements to The Sproutie. I would rather incorporate them here, rather than into subsequent, and separate posts. That way, if you are thinking of making your own version of this receiver, you can get all the latest updated information by reading this one (rather long!) post, instead of checking my entire blog for updates. As of February 2015, I have filled the entire cigar box with coils, with one to spare (that one is plugged into the receiver). The latest coil I made was for 17400-18200KHz to cover both the 16M BC band and the 17M ham band. 16M is just about the highest frequency shortwave BC band that is in regular use so I now have all the SWBC bands covered – most of them with coils specific for the individual bands. Here’s what my coil box looks like now. The unmarked coil sitting at the top of the box is the experimental one for 24-29MHz –
56 thoughts on “The Sproutie – A General Coverage Regen Receiver with Plug-In Coils”
Wow, so many memories – I too remember yearning for the HAC short wave receiver as always seen in the back of PW and Short Wave Magazine. I never owned one but did build an equivalent receiver designed by G3OGR using god Denco Plug in coils sometime in the late 1970’s. Really enjoy your posts Dave, and the wonderful photographs of your excellent craftsmanship.
Looking forward to reading more soon.
Regards, Steve. KC0NGU/G0CPV
That is absolutely a beautiful receiver, I can’t wait to hear it.
that’s a pretty sweet looking rig. Look forward to hearing some of the recordings you made off it
Thanks for a great blog, I always enjoy it. Would you post the dimensions of this latest project chassis you had commissioned?
Randy KD8SYS (Former resident of Oakland and Berkeley ’70-’84)
Hi Randy – you’re a long way from Oakland and Berkeley now! Sorry that I forgot to include the dimensions of my chassis. It is 9″ wide by 6″ deep, and the front panel is 9″ wide by 6 1/2″ tall. As you can imagine, the cost was quite a bit more than buying an off-the-shelf size Hammond chassis, but this one was made of thicker aluminum, it was made to the exact size I wanted, and Terry punched all the main holes for me too, so it was well worth it. I really wanted this receiver to be one that I can be using years from now, so it made sense to spend a bit more to have just the right chassis for the job.
Good luck if you have a go at building it, and I’ll be happy to answer any questions you might have,
Indeed I am… I received my electronics ed @ Laney College!
Thanks for the info. I intend to have the chassis fabricated at my place of business, collect some parts and go from there. My last project was a Manhattan version of the SW40+ . Worked out well except for the matched 4MHz xtals which I didn’t have so used some SMT 4M’s which show a LOT of attenuation. Built an RF boost circuit but haven’t tried it out as yet. I’m a hobby jumper it seems and I pursue my interest till it’s all gone, then flounder for a few weeks looking for an inspiration (hate that very uncomfortable!). Then jump all over that then rinse and repeat….
Randy – I know exactly what you mean with the changing interests. I blame it somewhat on being INTJ, if you believe those Meyers-Briggs characterizations. All I know is that my interests are very narrowly focused, and if I’m not interested in doing something, it’s almost impossible to get me to pay attention. However, once I am locked onto something, I can focus on it until I’ve reached my goal.
If you send me an e-mail (my e-mail address is good on QRZ), I can e-mail you some schematics and supporting information,
Gosh you do good work! I’m amazed!
Thanks Dan. It’s a labor of love, for sure.
Just in case anyone is duplicating: the schematic of the “Sproutie” AF board seems to be missing the positive power connection to pin 7 of the AD820. From the pictures you can see that it should go to the little +12 power bus .
73 – Paul – K0EET
Thank you very much Paul. I really appreciate the trouble you went to in order to let us know. I have changed the schematic to reflect that error. I may end up re-drawing it so that area is not as cluttered but at least now it is accurate. I hate to think of anyone building this and not being able to get it to work due to an error on my part.
A very nice regenerative receiver with Q-Multiplying and detecting separated into two distinct stages.
I see that the AF preamp stage with 2N3904 has been coupled directly onto the source of the infinitie impedance detector J310. This is not a good idea, because when the Q-Multiplier is oscillating, detection of the RF-voltage over the tank circuit will change the bias conditions of the infinite impedance detector. This will upset the bias of the AF preamp stage which can cause malfunctioning of that stage.
A Collpits oscillator which is used here, is only suitable for a small band coverage, if you want to use this receiver for a wide bandcoverage with a tuning capacitor of 500 pF you will have to modify the Q-Multiplier into a Hartley oscillator. The Q-Multiplier’s emitter resistor of 3k3 can be made adjustable to obtain a smooth and backlash-free regen control.
Thank you for that, mast.. I always appreciate it when anyone goes to the trouble to comment on the circuit of a project. Good point about the input coupling of the AF preamp. I haven’t experienced any issues, but it would be a worthwhile modification to couple those stages capacitively and bias the 2N3904 preamp separately.
I believe that one or two folk were thinking of duplicating this circuit for a wider band coverage, so thank you for making the point about the oscillator.
Note – I just realized that I have been using this receiver almost exclusively to listen to AM SWBC stations, so wouldn’t even notice an issue with the oscillation of the Q-multiplier affecting the operation of the infinite impedance detector. The same method of coupling is used in the WBR, however, and I didn’t notice any issues while listening on SSB, but I do see your point.
Fantastic looking project, Dave! Your documentation and presentation are first class. Congratulations are in order. I was considering duplicating your project and noticed the capacitor connected from pin 7 on the plug in coils to the source of the the J310 RF amp does not have a value?
Also as 73 – Paul – K0EET mentioned:
“The schematic of the “Sproutie” AF board seems to be missing the positive power connection to pin 7 of the AD820. From the pictures you can see that it should go to the little +12 power bus.”
You have indicated that this has been corrected on the print, but I only see pin 7 connected to ground through a .033uF cap. Could you please elaborate on this? Thanks and congratulations again. I would love to hear the Sproutie and see it in action on YouTube.
Aaaron / N9SKN
Aaron – those missing items you mention (the connection from pin 7 of the AD820 to the +ve rail, and the value of the capacitor from pin7 of the plug-in coil to the source of the J310) were corrected a month or two ago. Try clearing your cache to see if your browser will upload the current schematics. Let me know if that works. If not, I can e-mail you the correct schematics, but hopefully, that should do the trick. The cap from the plug-in coil to the source of the J310 is 0.01uF, incidentally.
Did you see Mast’s comments above yours? He indicates that it would be better if the source of the infinite impedance detector J310 were coupled indirectly (most likely capacitively) into the 2N3904 AF preamp. This is not going to be an issue if you are using the set to receive AM stations. I haven’t tried this set with SSB, but I used the same circuit configuration with my WBR and it does a fine job on SSB. It’s something to be aware of though. I may drag out my Sproutie to see how it performs on SSB and consider a modification if necessary. However, I can testify that it works well on SW AM broadcast stations, which is what I built it for. Please feel free to comment here more if you wish, or to e-mail me directly (I’m good on QRZ).
The only video camera I have is an old one that has rather poor video quality. If you’ve seen my other videos, you’ll have an idea. However, I may make and upload a brief video using this camera. It would probably be better than nothing at all.
Dave thanks for the browser refresh tip, all is well here now. Your Youtube videos are great BTW. That video camera is fine. I was actually thinking of the Sproutie for some CW action. 73’s Aaron
Wonderful piece of art. Glad to see there is still people with a gift for real good and solid engineering.
I must have missed this blog post a few months back when you first put it up, but just caught wind of it on YouTube. Incredible build and great write-up! The videos are great and hearing your demo of it makes me think its about time I start working on one. Never had a regen before and I think it would make a great wintertime project.
73, and thanks again for such a great article
A thing of beauty, Dave.
I too had an HAC as a boy. I think it was for my 12th birthday in 1965. I’d been using an ex-RAF R1155 that my dad picked up in Lisle St up to then but I wanted something I could hack about with. Also, the voltages in the 1155 were a bit off-putting. It sat next to my bed, and as it had no cover, on more than one occasion I got a jolt from it.
I used the HAC for ages, but eventually I replaced it with an Eddystone. Not appreciating the long-term value, sometime later I hacked the aluminium chassis apart and used it for making mounting brackets on my motorbike!
All of this was for SWL’ing. I didn’t get into amateur radio until I was in the sixth form, and then didn’t get licensed until the late 70’s.
73, Gareth, M5KVK
There were a few tube receivers I completely destroyed as a youth when I didn’t know any better Gareth. Sure wish I could go back in time and save them, though I didn’t have anything as nice as an Eddystone. One of them was my brother’s portable Ever Ready receiver, using miniature tubes (ooops, sorry – valves) which switched on automatically when the lid opened. I tried to fix it, and a few hours later it was in several hundred pieces!
It’s good to hear that a few others also have fond memories of the HAC receivers.
AA7EE (formerly G4IFA and G8RYQ)
Nice article – I had the HAC and the 90V Ever Ready battery. Have been thinking of making a regen receiver to play with now,
You have the strongest encouragement from me to build a regen Jon! I’m glad I’m not the only person who remembers (and used to use) the old Ever Ready 90V batteries. I was beginning to feel like an anachronism!
73 – and build that regen 🙂
Wow. You’re an ARTIST! Beautiful craftsmanship.
Excellent work beautifully constructed Reminiscent of the plate wiring we had to do on custom relays set on Post Office Telephones Where do the octal plugs come from though ? I have made a set of similar design designed by Raymond Haigh I believe. Has anode bend type detector and uses D type computer plugs for coil mounting. Your plug in coils look far easier to make and solder. D conectors are just to small for my eyes. I will make a sprouty and tell how it compares with Haighs design.
All the best.
Chris – I got the octal tube bases from Angela Instruments in Annapolis. They have a website and sell on eBay too. I believe the bases are manufactured in China, and are most likely available from other suppliers too.
Got the octal bases Dave, thanks for info. I put a sproutie together using a TDA 7052 as the AF stage. Could not get the RF stage to work so substituted a grounded base circuit pinched from the Raymond Haigh regen which was in an issue of Every Day Practical Electronics.
Works pretty well except noise going into oscillation is quite loud and speech in SSB is harsh and not really clear, upper or lower sideband. Any suggestions ?
Performance otherwise is similar to Haighs design. Your coils are much easier to assemble than D plugs although getting the desired frequency range requires patience. I really enjoy looking over your site Dave, thanks a lot and many best wishes.
Chris – hope you get this, as I’m not sure if the blog is going to register this comment as a reply to your comment. I know the Raymond Haigh circuit of which you speak, though I haven’t built it. It uses a separate tickler winding, and a variable capacitor for the regeneration control. I’m afraid I don’t have any suggestions, as I have little to no experience with these types of regens. However, you might try reducing the amount of signal that goes into the front end – a variable capacitor should do the trick. Regens overload very easily. A good technique for receiving CW and SSB on them is to turn the AF gain up to maximum, and keep the signal injection low by judicious use of an “RF gain” control. It’s the same way we received SSB on older receivers with diode detectors and BFO’s.
Let me know how that works out.
73 for now,
The way you constructed the receiver, built the cigar box with coils, everything is amazing. Beautiful.. Your are a very talented DIY
Thank you Raducu. I appreciate that!
Excellent project. I am wondering about the size of the pcb material you mount the MePads on; both for the Sproutie and the Sproutie II?
It’s about 0.06″ thickness. You can get thinner board, but I figured that it helps physical stability, and therefore the frequency stability of the RF board. In the Sproutie, the size of my RF board is 1.5″ x 4″ and the AF amp board is 1.75″ x 4″. The sizes I used in the Sproutie MKII were very similar, if not exactly the same.
Thanks for that info. It looks like the filter boards are also about the same size? Makes stacking them easier. Starting to gather parts but haven’t decided which one to build. Main hangup is the dial. Ones in good condition are few and far between… and costly.
Tnx again, PJH, N7PXY
PJ – this blog won’t allow me to reply to your reply. It only allows a maximum of 2 replies to a comment, so I’m posting a new comment here and hoping that you see it. I just turned my Sproutie MK II upside down and measured the boards. They are all 1.75″ x 4″ – the RF board, the main AF board, and all the filter boards. I’m not sure if I mentioned these measurements anywhere in the blog-posts, but it’s very possible that I didn’t, as they are not critical. It’s more a case of picking a size that suits your building style, and ability (or willingness) to fit things into a small space – or not, as the case may be.
Dave, Thanks and I did get the info. I have never built using the ‘Manhattan’ style and I do admire the ‘geometric’ layout of your build so I am going to give it a try. I will probably build the original Sproutie as the dial I have better suits that one. I have most of the parts except the octal socket bases. Found them on the net so good to go. Just have to finish a couple other projects first.
73, PJH, N7PXY
PJ – The schematics of the 2 Sprouties only differ in the audio filtering used. If you find the AD820AN in the original version to be a bit pricey, you can always build just one filter from the Sproutie MK II using the much cheaper 5532 dual op-amp chip. For general listening, I’d recommend one of the 2-stage (4th order) filters, using both op-amps in the 5532 for 3KHz or 4KHz bandwidth. The 3Khz one is a touch narrow for broadcast SW listening, but you’ll be surprised how fast you get used to it, and it does cut down on static well – it’s the filter I use most of the time in mine, somewhat negating the need for the multi-position filter switch. Use whatever dial you want, on whichever version you build. There is no such thing as a definitive version. Best of luck finishing up those other projects!
73 for now,
So far the hardest things to find are the variable capacitors. Sat down last night and made up a BOM from the schematics. I will verify it later this afternoon. Thanks for the help and encouragement.
Totally identify and I too lusted after an H.A.C. “one-valver” and the awesome “Model K” as advertised in those wonderful 1970s Practical Wireless magazines when I was a young teenager in Scotland. Alas I never received the promised “descriptive catalogue” I sent for, so never got one (I probably couldn’t have afforded one anyway, but we can dream…).
Years later, and after a move to Essex (England) for college and work, the shortwave bug bit again and I bought a brand new Sony ICF-SW7600 at a shop in Tottenham Court Road, London. That and a copy of “Passport to World Band Radio” and I was in hog heaven. Wow! HCJB, VOA, Radio Moscow, SRI, YLE, BBC World Service, etc. etc. I later bought a Ukranian Vega Selena “spy radio” too (remember those?).
Then, years later, after a move to the U.S.A., I got my Tech Plus amateur radio license (at Plymouth, Cape Cod airport no less 🙂 and later upgraded to Amateur Extra Class. It’s been a fun radio journey and it all started with Practical Wireless and advertisements for the H.A.C. “one-valver”. Thanks for the memories 🙂
Wow Rob – we had similar beginnings. It’s great to hear from someone who grew up with many of the same cultural radio reference points that I did. My HAC really wasn’t much of a performer – the regens I have built as an adult, such as The Sproutie, are far more impressive. To a teenage boy though, anything you can plug headphones into and hear the world with, is a magic box.
That ICF-SW7600 must have made you feel like the king of the shortwave hill! We are lucky to have experienced the SW broadcast bands back when they were still packed with big signals from so many countries. Sometimes, I wish I could bring those days back. Thank you for sharing your memories. I only vaguely remember the Vega brand, and not the Selena model, I’m afraid.
Thanks for your response Dave and it looks like you jumped the pond too : ). Yes, last year I bought and got fixed up, a 1962 National NC-140 and although I knew it going in, I was kinda sad that all those wonderful stations that I listened to throughout the 1980s and 90s are no more (HCJB was the XYL and mine’s favorite). Fortunately there are still a few English language shortwave stations on the air, but yes, we were lucky to have lived through some of the glory days of SWL. You would enjoy the book “Listening on the Short Waves 1945 to today”, available on Amazon, etc.
I did end up getting my regen though (a Heathkit GR-78 and an MFJ 8100). Amazing performance for 100 year old science.
73 OM ..
I saw an MFJ8100 at the vintage radio swap meet in Alameda a month or two ago. It looked quite out of place next to the wind-up gramophones and tube table radios of yesteryear. I should have put it out of it’s misery and purchased it, but I’m just a little too good at saving money, so held off!
Yes, regens do still amaze with their good performance for such circuit simplicity. Some folk dismiss them as toys, because they have only experienced poorly designed and/or built examples.
It’s odd to think that we experienced something which will never happen again, when we were listening to bands full of big SW broadcasters in the past. It’s one of the disquieting aspects of getting older – that we remember things which are no longer a part of our way of life. My grandmother lived to be over 100. I can’t even begin to imagine how she must have felt!
Thanks for the book recommendation Rob. I will look out for that.
Actually, for the record, my tube regen was a Heathkit GR-81, which *was* a regen (it wasn’t a GR-78). ‘ Funny that you and I, from similar beginnings, ended up in NorCal too; where short wave reception isn’t the best 🙂
The little MFJ-8100 is fun too but has very touchy regen (unlike the little 1 tube 1-Der 40 QRP transceiver I built and regret selling). It’s missing “medium wave” too.
Yes, I once read that when you get to a certain age, you no longer want to live because the world has changed so much ( although my Dad who was old when I told him that and lived to 81 said otherwise ;^) ).
Do look up that book as I’m sure you would enjoy it.
Oh, re. The Vega Selena, it was widely advertised in regular newspapers by a company called Scientific and Technical or something like that. It was during the Cold War and was often referred to in their adverts as a “spy radio”; probably because it was manufactured behind the iron curtain. It was a large analogue portable, a bit like the transistorized Zenith Transoceanics, with a wooden case and was actually quite a good performer. Very similar to the VEF xxx radios that were popular at the time. Since then there have been Transoceanics, tube and solid state, Grundig Satellit’s, Palstars , Sony 2010s and you name it across my listening post. Happy Days 🙂
My eldest brother bought a large Vega portable radio around 1960. It had a thick plastic case and the coils for the various wavebands (6, I think) were switched into circuit in what looked like an all-plastic version of the TV VHF turret tuners that were used then. If you switched to the higher frequency SW bands, it could blank out the TV on 63-66 MHz (UK channel 5). My father owned a hardware shop and sold the large Ever Ready 90V + 1.5V batteries for valve portable receivers. The 1.5V section often ran out before the HT and customers often brought them back to make sure they purchased the correct replacement. We used these old batteries, often two in series, as replacements for the 120V HT Battery in our accumulator powered radio in our bedroom. We got good reception of the BBC on 25 & 31m bands as we were only 15 miles from the transmitter at Rampisham Down in Dorset, South West England.
Thank you Rob and Ian, for your great recollections of the Vega receivers.
Thank You so much for this. I will save your site and likely make much use of it. I am retired from RF engineering but love the simpler things, especially when a lot of effort goes into a project.
It’s the simplicity of regen designs that appeals to me Rodney, combined with the relatively good performance. I’m glad you enjoyed the post, and hope you got something useful out of it.
Sometime ago I tried to build a similar little regen set, but it performed poorly. It was built in a similar chassis box as yours, with home made coil forms (octal bases from dead tubes with varnished cardboard tubes). I used a BCB/FM tuning capacitor with 25pf, 365pf, and 140pf sections that could be selected via jumpers in the socket as you did. The vernier dial is one of those 3″ Japanese made types that RatShack sold in the 60’s, I got two of them cheap on ebay, but I also have a National N dial in the junk box. The Jap dial works very nicely and has the vernier scale. I used an old RCA CA3020 ic in the AF stage, it should have as much gain as the LM380 plus the 2n3904 does. I used point to point wiring with transistor sockets, so I can easily rewire the set to use the same circuit that you did in the RF section, and I’d like to try that. Where did you get those NOS octal tube bases?
Scharkalvin – those octal tube bases are not NOS – they are actually new. I got them from Angela Instruments in Annapolis, who have a website and sell on eBay too. It’s worth comparing the prices on their site with their eBay prices as, depending on the quantity you purchase, there is a small price difference. Best of luck with your rebuild!
Very nice build on the regen Sproutie . Please an you tell me what you use to do your aluminum folding and cutting, do you have a you tube presentation on chassis bashing .
I don’t make my own chassis. As mentioned in the post, I used the services of Seaside Chassis.
73 for now,
I built a Sproutie!
It’s not anywhere near as tidy or professional as yours but it works so I wanted to get in touch to make a comment. My desire to revisit a regen was prompted by a rally find: a beautiful 36:1 slow motion drive with anti-backlash gears and everything. Just £2 was a steal. The rest of my Sproutie was pretty much out of the infamous junk box in my shack, including the chassis which I made from an aluminium front panel riveted to a tin plate chassis. Unfortunately though the best variable capacitor I had to hand was way too high in value so I pulled out most of it’s vanes. Sacrilege! I’ll be on the lookout for a better one at this year’s rallies. I’ve only built one coil so far which covers the 40M ham bands and the adjacent BC bands. The valve bases you used are rare as rocking horse crap over here in the U.K. I’ve finally found some on Ali Express so I’ll need to wait for those. I used a bit of a cobbled together arrangement to get things working, although the coil is to one of your designs. So, I have a question. In the blurb for the mark II version you mention that it might be worth experimenting with the 39pF capacitor that feeds the oscillator and in your opinion could be much lower. Well, in my Sproutie I can’t even get it to oscillate with 39pF and had to increase it to 47pF for it to work. To be fair, I didn’t have any 330pF caps for the oscillator so I used 300pF which I did have. I can’t imagine that would make that much difference but maybe you might shine some light on it.
Incidentally, I also used a CA3140 op amp in the audio board and it works just fine. I have to agree, it’s a great audio design and much better than the LM386.
I find my Sproutie is a little microphonic. My shack is a shed so the floor isn’t solid. Walking while tuned to CW makes it change pitch. Man that’s sensitive. My link cables are admittedly a little longer than yours but I used seriously thick cable. It’s also very sensitive to me !
I’d like to put it in a box but now I’m wondering if It ought to go in metal box or even line a wooden box with tin foil? Any thoughts?
I agree though that it’s fun to use. Yes it’s a little tricky and prone to overloading but once you recognise the sounds it’s easy to back things off. I’m also running mine from a outside aerial and it certainly pulls in the signals. Thanks for posting your article and the reason I chose to make a Sproutie over the myriad of other regen receiver designs on the internet was both your very detailed article and the videos of you operating it. It proves the design works.
Congratulations on building a Sproutie, Mark! I’m afraid I don’t know why your set won’t oscillate with a smaller value of coupling capacitor than the 47pF you used, though if it works with that, that’s fine.
Microphony and frequency instability can happen with any regen receiver. Short stiff leads in the frequency sensitive circuits and overall stout construction are your best defense. As you probably read, my Sproutie MKII is slightly microphonic under certain circumstances, while my original Sproutie doesn’t suffer from it at all. My Sproutie MKII is built on a much larger chassis, which I think is the main reason. There’s a much bigger mass of metal to flex. Slightly longer leads don’t help either. Regen receivers can be quite unforgiving when it comes to physical construction!
If I were to build one of my Sprouties again, I would put it in a completely enclosed metal box, as opposed to a partially open metal chassis. That’s something of a personal thing though, as I’d like the option to use the regen as a tunable IF on a lower frequency band, such as 2.5 – 3MHz, with a series of outboard converters for the different bands. A metal box would prevent any signals on the IF frequency from getting into the receiver. As for the choice between lining a wooden box with foil, or using a metal container, I’d opt for the metal, as it sounds more robust. Foil can come unglued and tear, and is harder to make electrical connections to.
Yes, regens do overload easily. This is particularly noticeable on SSB and CW. When using it in these modes, I keep the AF gain at max, and only advance the RF gain enough to ensure adequate reception. It’s the same technique we used with older superhets that had a BFO and the standard AM diode detector, instead of a product detector.
I checked the UK eBay site, and tube sockets, as well as bases, are available on it. The ones I got were from a US supplier, but I’m pretty sure they were originally manufactured in China. They are most likely the same as, or very similar to, the ones being offered on eBay. They’re not that cheap though. If you’re ordering parts from several different suppliers for a project like this, the cost can add up fast!
I’m really happy that you found my blog posts and videos helpful. Thank you for letting me know. I built these receivers a few years ago, so have to stop and think when answering questions about them. I have forgotten some of the stuff, and have to re-read my own blog-posts in order to remember!
I’m still curious about that 47pF capacitor, and why you can’t get it to work with anything smaller………
Cheers for now,
I found your side – very nice, congratulations. I want to ask something: I see small “cubes” at Manhattan circuits. Are these factory products (did it work) or did you make it yourself? If factory, where can you get one?
Thanks in advance for answering.
They are here –
If you like smaller ones, they are here –
The pads for IC’s are here –
If you build with surface mount IC’s, then you need these –
There are cheaper ways to make pads for Manhattan construction, but these are convenient, and they look great. I’m a big fan.
73 and good luck with your building!
Mni tnx information! This is more than I hoped for! Thank you very much!
Then I ask how much they deliver to Hungary.
Good construction! 🙂
Hai Dave, what a wonderfull receiver and also loking nice to see !