Dave Richards AA7EE

October 6, 2015

Some More Sproutie MK II Videos

Since finishing The Sproutie MK II and publishing the blog-post on it a few weeks ago, I have been listening to it, winding an extra coil or two, and also attempting to tweak the active audio filters. Coverage of The Sproutie is now up to 18.3MHz, and while I know from previous experience that it will cover up to 30MHz, I am going to leave the upper limit where it is for the time being. Any new coils will most likely be wound for more limited coverage on specific bands under 18MHz. PS – I just spent part of the morning testing out the upper limit of the newest coil by listening to SSB on 17M, and it’s working great – quite stable too.

I had wanted to give the CW and SSB active audio filters more gain, to compensate for the fact that in those modes, the RF gain needs to be wound down to prevent oscillator pulling. Because the narrower filters, even if they have the same gain as the wider filters, give the perception of lower volume, I wanted to design them with higher gain to compensate. Currently, the narrowest filter, a 700Hz low-pass, has a gain of 20dB. I tried building 700Hz low-pass filters with gains of 46 and 34dB, but they both oscillated, putting out a square wave with 10V amplitude at a frequency of somewhere in the region of 100-150Hz. I made sure to keep the Q below 3 – in fact the highest Q stage in the 34dB filter was just a little over 2, but this didn’t help any. For the time being at least, I have decided to keep the current filters as they are. If you view the videos, you’ll see that The Sproutie does indeed work on SSB and CW. If receiving a weaker station for which the set could use a little more gain, plugging headphones in helps and at this point, it’s a compromise I’m willing to make. Trying to build the perfect regen is a rabbit hole from which it sometimes feels as if there’s no escape, so I decided to draw a line in the sand and leave things as they are.

Once again, I feel as if I should apologize for the quality and resolution of these videos. I just entered the 21st century a few months ago with the acquisition of my first smartphone, a first generation Moto G. It’s a budget model, so doesn’t have the best video. It is an improvement on the videos I used to post from my decidedly old Canon Powershot A80 though. The one thing the videos do achieve, I think , is to give you some kind of feel for what the receiver is like to operate. For detailed views, the still photos are the way to go.

This one shows how a regen, if you nudge it into gentle oscillation, can provide some carrier injection for reception of weak AM stations –

Here’s the 25M SW broadcast band –

And another video on the 40M amateur band on CW and SSB, with a special brief guest appearance by Jingles the blind kitty –

September 14, 2015

The Sproutie MK II HF Regen Receiver

NoteIf you have read this article before and are checking back in, it would be a good idea to clear your cache, to ensure that you are viewing the very latest version of this post. I do add material and make corrections from time to time.

It’s been about a year since I finished building The Sproutie, and it’s been a good year. Of all my scratch-built projects, it has been the most satisfying to own. It works well, looks pretty good and also, there is always the lure of possible of tweaks and improvements. This is partially because it’s a home-brew project, and also because it’s a regen ūüôā It was really enjoyable to build a receiver with the basic circuit architecture taken from the 1930’s, but with a combination of solid state devices and lovely old vintage parts.

I have continued to occasionally purchase vintage reduction drives and variable capacitors. After using a National N Dial for the main tuning control in The Sproutie, I became quite pre-occupied with what, to me, is close to the ultimate dial and drive for an analog receiver – the classic National HRO micrometer-type dial and gear drive. I wanted to find a good example of one of these, and use it in a regen. ¬†I also spent quite a bit of time performing Google searches using phrases such as “best regen receiver ever”, and “the ultimate regen”. These are the kinds of things I search for when at a loose end, in the vague hope that I’ll magically find the most amazing regenerative receiver ever designed and built! One very inspirational regen I did discover while searching for the “ultimate regen”, was Jim K4XAF’s build of Bruce NR5Q’s “Ultimate Regen”. What a beautiful receiver! It’s a tube set, built on 2 separate chassis. One chassis contains the main receiver, while the other houses the power supply, the speaker, and the “Selecto-O-Jet” audio filtering. It makes use of a National HRO dial and gear drive for the main tuning, along with National “Velvet Vernier” drives to control the regeneration and variable antenna coupling. Now this was the type of regen that inspires true longing, and convinced me that as enjoyable as The Sproutie was to build and own, I needed to build just one more regen ūüôā

Initially, I was hoping to use a different type of circuit for this receiver from the tried-and-tested front end used in The Sproutie. I did build VE7BPO’s regen #4 and had some trouble with it picking up a local FM broadcast station. In retrospect, I should have realized that I have had this issue with other simple receivers at this location, until they were cased up and grounded properly. The problem seemed to be a little worse than normal, but this could well have been due to the amplification factor of Professor Vasily Ivanenko’s hycas detector. I gave up far too soon and headed for the security of the front end I used in both the first version of my Sproutie, and the WBR. It is, of course, the circuit used in Nicky’s TRF, as featured in issue 70 of SPRAT (with a few corrections and suggested mods in issue 72). Incidentally, “Bear” NH7SR built a very functional version of Prof V’s Regen #4 which he described in this thread over on The Radio Board.

However, I didn’t just want to exactly duplicate the circuit of The Sproutie, even if the new receiver was going to have a different physical form and different hardware. This new receiver would have to have some alternate type of circuitry that would make it worth building. I was interested in trying a different type of filtering in the audio chain, and a tip from Prof V in his Solid State Regenerative Receivers group on Google+ clued me in to a great tool for designing active audio filters (more on that later). The pieces were beginning to come together. I had a bunch of NE5532’s in my parts stash that had sat unused for a couple of years and it struck me that a regen which utilized a series of active audio filters for different bandwidths, switched from the front panel, might be an interesting idea for a receiver. The LM380 output stage I had used in The Sproutie works well, so I saw no reason to change it.¬†It is fairly low noise, a welcome factor that makes it possible to listen to a receiver comfortably for long periods of time.

Here’s the block diagram of The Sproutie MK II. As it contains 6 separate AF filters, I decided to also switch the +ve supply to the filter. A 5532 active filter draws about 7mA (14mA if using 2 x op-amp stages). Although it’s not a lot of current, it’s a fairly significant amount relative to the total consumption of this receiver if all 6 filters are continuously powered. One of the reasons I prefer solid state over tubes is the power efficiency, so no reason to keep all 6 filters powered if only one is being used at a time –

Fig 1 – Block diagram of The Sproutie MKII. Note that S1a, S1b and S1c are all part of the same rotary switch.

The front end, as I mentioned, is exactly the same one I used in the original Sproutie. It is the one used in Nicky’s TRF featured in issue 70 of SPRAT. I thoroughly recommend joining G-QRP. Your initial membership includes an archival DVD of past issues of the club magazine SPRAT, which is a very valuable resource for homebrewers. If you have access to this archive, you should also take a look at issue 105, in which a slightly different version of the same receiver is featured. It employs a simple passive LC audio filter, if you’re not keen on the extra complexity that my version here entails.

Here’s the schematic of the front end. The oscillator tank circuit has been simplified to just one variable capacitor, and all details of the plug-in coils removed, purely for the purposes of making the circuit a bit easier to understand. If I drew the octal coil socket without the coil (as I did with the schematic for The Sproutie) it would make the process of understanding the circuit diagram a bit less intuitive –

Fig 2 – The Sproutie MKII front end, with details of plug-in coils and fine tuning capacitor removed for simplicity.

Here are details of the coil base, using an octal tube socket. You can use any pin configuration you like – this is the one that worked for me. It is the same configuration as used in The Sproutie –

Fig 3 – Plug-in coil base wiring

The final AF amp is a simple LM380 circuit. It’s easy to build, is fairly low-noise, and it works. If you’re used to AF circuits which use an lm386 in high-gain mode, with a 10uF cap between pins 1 and 8, you are going to love the much lower-noise performance of this circuit! As well as a phone jack, I included a jack for an external speaker on the rear panel. It took me a while to figure out how to wire the internal speaker and the 2 jacks properly. ¬†I wanted the internal speaker to cut out if either headphones or an external speaker were plugged in. I also wanted the the external speaker to cut out if the headphones were plugged in. It’s a simple problem really, but simple things often elude me. I got there in the end –

Fig 4 – The AF output stage. The “bass” switch only gives a very gentle lift to the lower frequencies. The effect is so subtle that you won’t be missing much if you leave it out.

The thing that makes this receiver different from the original Sproutie, electrically speaking, is the bank of switched active audio filters. If you don’t want to be bothered with building multiple filters, and switching them all with a switch, you could permanently wire just one filter into the circuit. Another idea would be to replace this bank of switched filters with an adjustable filter made from op-amps, with the center frequency and bandwidth controlled by potentiometers on the front panel. Once you bring op-amps into the mix, all sorts of things are possible. Another idea suggested by Bear NH7SR, is a 5KHz audio notch filter, which could be quite useful for AM SWBC listening. The design tool that made all this happen for me was by Texas Instruments (thanks Prof V). There is an online version called Webench Filter Designer. It¬†has a user-friendly interface that actually made the process of filter design harder for me than the offline software they also offer, called Filter Pro. Use which one works best for you – they are both accessible from this page (opens in a new browser window).¬†Of the two, I recommend Filter Pro. You can use this software to design low-pass, high-pass, bandwidth, allpass (time delay) and notch filters. I stuck with low-pass filters. I was tempted to try a bandpass design for the CW filter, and may still do at some point. The CW filter I constructed was the very last filter out of 6. By that time, I didn’t have the patience for the slightly more complex design of the bandpass filter. I also rationalized that I might need to tune through a CW signal to hear the other side of it, if trying to escape QRM, so a lowpass would make this easier, as I’d be able to hear the signal all the way through to zero-beat and out the other side. This might simply have been my excuse for not wanting to build a bandpass filter ūüôā

I wanted a “straight-through” position to give me something to compare the other filters to. All the filters, with the exception of the narrow CW filter, were designed with a 6dB gain, so I designed my “straight-thru” filter with a 6dB gain also, so I could step through the bandwidths seamlessly. If doing this again, I would have given the filters a bit more gain. I’ll explain why later. Dan N7VE gave a talk to the Arizona QRP Scorpions a few years ago on (among other things) designing active audio filters. It’s definitely worth taking a look at his presentation, which is available here.¬†In fact, I wish I’d paid attention to it before embarking on designing the filters for this receiver, as I would have tweaked some of the resistor and capacitor values a bit. Dan explains how it’s desirable to keep the resistors in the main signal chain fairly low in value, to avoid noise. He recommends trying to stay under 1K. I only read the presentation before designing the very final filter – the CW one with a cut-off of 700Hz – so while my resistor values in that filter are nice and low, they are not quite so low in the others (though in my defense, they are not atrociously high either).

Here’s the first, and widest filter. As far the ear is concerned, it’s not really a filter, as it has a cut-off set at 20KHz, with a gain of 6dB –

Fig 5 – The “straight-through” filter (an LPF with a cut-off of ~20KHz)

I wasn’t interested in the shape of the response as, for this stage, all I wanted was effectively an unfiltered stage with a gain of 6dB. For this reason, I used just one half of a dual op-amp 5532 package as a real-pole filter. Filter Pro doesn’t show the power supply and biasing arrangements, so I added the 2 x 47K resistors to keep the input biased at about half of the supply voltage. I also added the 10uF capacitor, which keeps the bottom end of the 1K resistor at ground potential for audio signals, while blocking the DC bias. I also added the lowpass filter formed by the 10 ohm resistor and the 100uF electrolytic on the supply line, as well as the 0.1uF ceramic RF bypass cap on pin 8 of the IC (mounted close to the pin). I don’t know how essential these 0.1uF caps are, but the datasheet suggests them, and they can’t do any harm.

The other filters were all 4th order low-pass filters (2 stages = 1 x 5532 dual op-amp package), with the exception of the 2.4KHz filter, which was an 8th order low-pass filter (4 stages = 2 x 5532 dual op-amp packages). The 8th order filter has a sharper cut-off, of course. Feel free to design your own filters, with the help of Filter Pro, for whatever cut-off frequency and rate of roll-off you wish. I’ll show you the R and C values I used for my filters but you might want to fiddle around with the software and come up with your own values that keep the R values in the main signal chain at or below 1K, if possible. The resistors in the first stage of the filter are particularly important, as the noise they produce is amplified more than noise produced in later stages. Just click on a component in Filter Pro, enter a different value, and hit return to see what new values of the other components the software has calculated. A bit of trial and error should get you close. Also note that you can specify the series of resistor and capacitor values you want to use (E96, E48, E12 etc), and watch how the filter response curve changes as you change the tolerances and values.

First of all, here’s the gentler roll-off 4th order filter that uses just one 5532 8-pin dual op-amp IC – or use the op-amp of your choice. I chose the 5532 because I had a bunch of them in my parts stash and because they are the 2N2222 of the op-amp world – plentiful, reasonably priced, and all over the place –

Fig 6 – Schematic for the gentler roll-off 2-stage LPF

Here are the component values I used for my 4th order filters –

Fig 7 – Component values for the 2-stage filters in my Sproutie MK II

For a sharper roll-off, an 8th order filter, which uses 2 x 5532 dual op-amp packages (or equivalent) –

Fig 7 – Schematic for the 4-stage sharper roll-off LPF

The 2.4KHz 8th order filter I used, although a bit on the narrow side for SSB, is good for listening when there are nearby stations higher in pitch that need cutting out. If you think about it, this 2.4KHz LPF is going to sound roughly like the 2.1KHz filter in a regular SSB rig. The reason for this is that your regular SSB filter is a bandpass filter, with the bottom edge being set to cut off at about 300Hz. This means that a 2.1KHz SSB bandpass filter will pass frequencies up to about 2.4KHz (2.1KHz + 300Hz). Here are the values I used in mine –

Fig 8 – Component values for the 4-stage filter

After I had built the receiver and all these filters, and done some listening, I concluded that for SSB and CW, a bit more filter gain would be helpful. The set has plenty of gain when listening to AM but on CW/SSB, the RF gain has to be wound right down to prevent the oscillator pulling. This creates a need for more AF gain in the CW/SSB modes. At the time of writing this, I have only just finished building this set and have no enthusiasm for building more filters. I actually had to build 8 filter boards to get the 6 that I used, and 3 front end boards to arrive at the final one. Together with the physical side of the construction, I am tapped out right now and have no desire to construct anything else at all for a while!

If you want to use this receiver mainly for SSB and/or CW, you may want to experiment with the value of the NPO capacitor in the front end that connects the hot end of the main tuning coil to the base of the 2N3904 oscillator transistor. It is listed on the schematic as being 39pF, and that is the value I used. However, it is possible that a lower value will cause the oscillator to pull less on strong signals. Of course, the lower value might also reduce the signal strength into the detector which will put you back to square one. It’s worth trying though. I’d be tempted to try a value as low as just a few pF. Remember that changing this capacitor will affect the frequency coverage – particularly at the top end of each range.

When building the filters, I originally built the 700Hz CW filter with a gain of 6dB, like the other filters. The idea is that if they all have the same gain within their passband, the operator can step through the different bandwidths without a change in the volume of the wanted signal in the speaker. This was the way it worked except with the 2 narrowest filters. The 2.4KHz 4 stage filter had a slight, but noticeable drop-off in volume. The effect was very pronounced with the 700Hz filter – so much so that I redesigned it with a gain of 20dB and still found that there was a slight drop-off in volume within the passband as compared to the other filters. I don’t know the reason for this. EDIT – Thomas LA3PNA Tweeted the following explanation – “The perceived loss when changing filters is because the power delivered to your ear is 10log(BW of filter) and less with less BW. So basically, the reduction in noise makes it sound like the volume goes down” ¬†He also gave a very useful tip for adjusting the gain of the filters so as to preserve the perception of constant volume – “I like to add gain in a filter circuit after the formula 20log(bw/orginal bw) for AF filters” ¬†That is very useful information Thomas. I’m a little tapped out after building The Sproutie, but if and when I decide to revamp the filter bank, I’ll be paying attention to this formula.

I may, at some point, rebuild the 3 narrowest filters with higher gains. If that ever happens, I’ll report the results here in this post. Incidentally, at this point, allow me to say one more thing about the filters. If building and wiring up all these filters sounds like it is making the construction of a regen overly-complicated, I can definitely sympathize. If you want to use this set for CW, SSB and AM and you want to permanently wire in just one filter, I’d go for a 4th order (2-stage) LPF with a cut-off of 3KHz. The one I have is perhaps a touch wide for SSB (it’s roughly equivalent to a 3.3KHz passband filter, as explained earlier) and a bit narrow for AM broadcast, but it’s a good compromise for both. If it were the only filter I had, I know I would get used to the sound of it. As for the gain, mine has a gain of just 6dB, but I’d like to up it in order to have a good volume when turning the RF right down, as is necessary to prevent oscillator pulling on SSB/CW. I can’t know until I’ve tried it, but I’m thinking something along the lines of 26dB gain. Just make sure to be careful when on AM, as you may find that you have way more gain than you need – so keep an eye (and a hand) on that RF gain control.

A big part of the inspiration for building this receiver, as I mentioned earlier, was the physical form of K4XAF’s version of NR5Q’s Ultimate Regen. In the search for a National HRO dial and gear drive in really nice condition, I bought several, and finally came up with a dial and drive combination that just cried out to be included in this receiver.¬†This gear drive has a shaft rotation limiter, which was perfect, as the tuning capacitor I wanted to use didn’t have any kind of rotation limiting built in – it was the capacitor in the first photo in this post – a Hammarlund MCD-50-M. The final M stands for midline, referring to the fact that the off-center shaft and shape of the vanes help to make the tuning a lot more linear than with regular variable capacitors. With a standard capacitor, you’d find that the frequencies would become very compressed at the top of the tuning range i.e. the tuning would get a lot more fiddly. Try to get a midline unit. I believe they also go by other names, depending on the manufacturer.

Of course, a big dial and gear drive need a big chassis, and Terry from Seaside Chassis, who made the chassis for The Sproutie, came to the rescue again. I decided to use a chassis and front panel that would be compatible with 19″ rack cabinets, for a variety of good enclosure options. A chassis that big needs to be fairly thick in order to still be stout and solid. Terry does offer the use of 12 gauge aluminum for bigger enclosures, and I wanted this receiver to be big and solid (although compared to your average boat anchor, it’s still relatively light). As well as a large, stout chassis, I decided that I wanted to try designing a custom front panel with the services of Front Panel Express in Seattle using their free design software. Right at the beginning of this whole project, in the first month or two of 2015, I downloaded their software and casually laid out a very rough front panel, mainly for the practice, and the fun of learning something new. As the project progressed, I’d spend a few weeks working on circuit boards, then go back to the front panel, then do a bit of work on the plans for the chassis, to send to Terry. I had an idea that, with a bit of luck, I’d complete the whole thing in or around the fall, and that’s how it worked out. At no point did I rush though. Why rush? Besides, the longer a project takes, the less it costs per month. I could see that building this regen in the way I had chosen to build it was not going to be a cheap affair, so I took my sweet time.

Here is the chassis as it arrived from Seaside Chassis, along with 2 side braces for supporting the front panel, 2 mounting brackets for the main tuning capacitor, and 2 mounting brackets for the regeneration pot. I only needed 1 of each of these brackets, but like to have extras on hand. As it turned out, an extra bracket was needed to help secure the main tuning capacitor which I forgot to ask Terry for, so I put in an extra order. The shipping from Canada dwarfed the cost of the bracket but at this point, it was easier to ask him for it than to find someone local and besides – I just wanted him to fabricate all the chassis components. Terry’s work is first-rate. It’s good to give him as much relevant information as you can. Simple drawings with penciled-in dimensions work well. If it’s important to you, remember to take into account the thickness of the aluminum if there are any dimensions that are particularly critical. Also remember that he is bending and fabricating these components by hand, so allow for a certain amount of tolerance in the final dimensions. Having said that, the chassis he supplied was remarkably close to the exact dimensions I requested, and within the tolerances I had allowed for. If you have any dimensions that are particularly critical or non-critical, I think this is all good information to pass onto him when making your request –

Figuring out exactly where to drill holes for controls in front panels and enclosures usually takes quite a lot of time. It’s a bit like a game of chess in that every decision you make affects everything else down the road. To make matters tougher, I have trouble thinking about more than one thing at a time, so juggling all the variables in my head takes a lot of thinking, measuring, and drawing. For front panels, I always draw the shape of the panel on a full-size sheet of paper, and place all the knobs and controls on it to see how they look in various configurations. Just when I think I have it right, I leave it and walk away, often overnight. On returning, I inevitably come up with an improvement or two. Building something like this is all baby steps for me. I am impressed and amazed by builders who claim to be able to throw something like this together in a few afternoons – this one took me over 6 months. Heaven knows how long a more complex receiver, such as a multiband superhet, would take me.

I took a great deal of time and care in designing the front panel. They are worth every penny, but they are not cheap. I didn’t want to make a mistake that would result in having to re-order the whole thing. So after checking, rechecking, going to sleep, then waking up and rechecking again, I went through this whole process several more times before finally clicking “order”. A week or so later, this beautiful 4mm thick aluminum panel arrived via UPS, packed with a little bag of gummie bears –

Gummy bears!

The front panel as it arrived from Front Panel Express, vacuum packed to a stiff baseboard. The metal ruler is 18″ long (the panel is 19″ wide).

Look at this beautiful, black anodized front panel!

I just couldn’t get enough of this thing when I first saw it –

There were some scratches in the black finish on the rear, but this is normal. I later found out that ¬†it is possible to add a note when ordering, to ask the people working with the milling machinery to take extra care with the back side of the panel. The front surface is guaranteed, but not the back. ¬†I decided I was OK with the rear of my panel as, well, it was the rear, and the bottom half of it would be in direct contact with the front of the chassis anyway –

You’ll notice a number of “blind” holes milled on both the front and rear. The panel is so thick (4mm) that controls sticking through both the chassis and this panel wouldn’t protrude far enough for the nuts to thread onto the bushings. For the RF gain, AF gain and filter rotary switch, the blind hole was milled on the front side, as the knob would cover it. For the phone jack and bass switch, the blind holes were milled on the rear. Here’s a close-up of the blind hole on the rear side for the bass toggle switch. You’ve probably figured (if you didn’t already know) that a “blind” hole is one that doesn’t go all the way through the panel –

After the initial euphoria of receiving this fantastic front panel had subsided a little, it was time to put some time and labor into making all the remaining cut-outs in the chassis. I had asked Terry to make the holes for the octal tube socket and the main controls, but there were others that still needed to be done. My usual method of making non-standard cut-outs and holes is very time and labor-intensive, but it works quite well. I mark the edges of the cutout with a pen or pencil, then with a hand-drill, drill lots of small holes around the perimeter. Then, with an old screwdriver, I knock out the piece of metal in the center, and clean up the edges with files, usually using a bastard file first, and finishing off with something finer. These photos should help illustrate the process. The speaker cut-out was inspired by a WW2-era British military R107 receiver that I owned as a teenager. It is simple – just 4 large holes arranged in a square. This is the “during” photo, showing the series of small holes drilled around the edges of the holes. The rectangular cut-outs to the right were made using the same technique, incidentally –

– and after –

Here’s another photo, taken a bit later during the assembly, showing the placement of some of the main components. This particular National HRO NPW gear drive, unlike most that I have seen, has a shaft rotation limiter. The tuning shaft is a little on the short side. I needed to mount the gear box as close to the front panel as possible in order to be able to mount the dial properly. If you scroll back and look at the photos of the front panel, you’ll see there are 3 smaller holes located around the main hole for the gear drive. These holes helped in locating the gear box as close to the front panel as possible (the 3 screw heads fit into the 3 smaller holes on the front panel). Most of these gear boxes don’t have this rotation limiter, so the extra holes won’t be necessary. Also, do you see the aluminum shaft couplers on the regen pot and fine tuning capacitor? Those are quality parts personally machined by¬†John Farnsworth KW2N. The one on the right is a standard 1/4″ to 1/4″ coupler, while the one on the left was made to order. It couples the 1/4″ shaft of the 10-turn regeneration pot to a short 3/16″ shaft that the National knob fits onto. I wanted to use the same type of National Velvet Vernier knob and escutcheon plate for the regeneration that I used for the fine tuning, but I didn’t want to use the 5:1 reduction drive. I wanted to use a 10-turn wirewound pot instead, as I like the feel of those pots. From the front (as you will see in later photos) the 2 National knobs and escutcheon plates look the same. However, the knob on the left is connected directly to the 10-turn pot and not to a National Velvet Vernier reduction drive. The black escutcheon plate for the regen control is spaced away from the front panel by one washer thickness, and bolted to the front panel with 4-40 hardware. It is not used for anything, other than looks.

Now, let’s look at some of the boards. They were built, as always, with W1REX’s very useful MeSQUARES and MePADS. This is the AF output stage and the 4KHz filter mounted on one board, and installed in the chassis. The idea was that this board, together with the main RF board, would form a working receiver, after which I could build and install the other filters, one by one –

Mounted above the AF output stage, on the stand-offs, is this next filter board, carrying 2 LPF’s. The first filter to be built was the 6KHz one –

Next came the 3KHz filter (in the foreground of the next shot). The grey rectangular poly capacitors were from Tayda Electronics. Thier prices are low, and the caps seem good. The resistors are 2 types – either 5% carbon film from the parts stash I had as a kid in England in the early 80’s. They lasted a long time, but I am beginning to run out of them. The others are newly-acquired Xicon 1% metal film parts, purchased in lots of 200 from Mouser –

The same board, taken from above (3KHz filter on the left, 6KHz filter on the right) –

The same board, with the 3KHz and 6KHz filters, mounted in the chassis above the 4KHz filter and AF output stage –

Here are 2 shots of the 4-stage (8th order) 2.4KHz LPF, with temporary leads in place for testing. It’s quite the QRM-buster –

At this point, allow me to introduce the main RF board. Electrically, it is exactly the same as the one in the original Sproutie. I tried a couple of small mods but went back to the original. So – nothing new here, except for a small physical detail that I learned from my experience with The Sproutie. There are 2 pads on the board that connect to the octal tube socket with (ideally) short, stiff wires. In the original Sproutie, I used very short lengths of solid 16 gauge wire. They were so stiff that, over time, with repeated insertions of coils, the wires placed enough stress on the pads to detach them from the board. It took me a while to figure out why the dial calibration was suddenly off by about 10KHz. The pads had only separated from the board by 1mm at most, so it was hard to see, but it was enough to throw off the dial calibration, and cause it to change slightly in an unpredictable fashion. I did 2 things to remedy this. The first was to replace these 2 wires with thick stranded wire, which I tinned thoroughly. The tinning stiffened the wire, but it still had more flex than the original solid 16 gauge wires. Secondly, I removed the 2 pads, and re-attached them with epoxy instead of superglue. Problem solved! ¬†When I built the Sproutie MK II board, I attached these 2 pads with epoxy (I used JB Weld). Superglue gel was used with all the other pads, as before. The 2 pads in question are at the very front edge of the board in the next shot. They are the second and third pads from the right. Missing from this shot is the 0.1uF capacitor that couples the audio to the next stage. There is also one extra capacitor that was part of a mod I later uninstalled. I’m showing you these shots to give you the overall idea of layout, what it looks like, and because it’s fun looking at circuit boards. For absolute accuracy of the circuit, follow the schematic –

The next 2 shots are the same board, but at an earlier point when I was using 1uF caps for interstage coupling. They are the 2 blue box-like caps. They didn’t make it to the final version of the board –

Here’s a wider view of the underside of the chassis at this stage of the construction, showing the main RF board wired to the octal tube socket, as well as the AF output stage with 4KHz filter, the 3KHz and 6KHz filter board on top of it, and the 2.4KHz filter board sitting on it’s own for the time being –

A closer view from a slightly different angle. At this point, it was beginning to dawn on me that keeping all this wiring tidy would take a bit more work than I had anticipated. I never did get the wiring as tidy as I wanted, but it’ll do –

This one’s a bit boring. It’s the “straight-through” real-pole LPF with a cut-off frequency of 20KHz, shown installed in the chassis on top of the 2.4KHz LPF –

and the 700Hz CW low-pass filter –

Here are all those filter boards stacked on top of each other. Looking at the left-hand stack first, from the top down is the 700Hz filter, the 20KHz “straight-through” filter and, at the bottom, the 2.4KHz sharp roll-off filter. On the right-hand side is the 3KHz and 6KHz filter board, with the 4KHz filter and AF output stage board on the bottom. You can also see the 6-position rotary switch that selects between the different filters. I had no trouble finding a 6-position switch with 2 poles but when I decided to also switch the +ve supply line to the filters, finding one with more than 2 poles proved tricky. I finally found it from a supplier of parts for musical instruments. It is distributed by AllParts, and is part number EP-0920-000. It is a 6-position 4-pole switch (one pole goes unused). Prices vary a bit, so search around for the best deal if you want this particular switch. If you want fewer filters, then you’ll probably find it easier to locate a switch that has 3 or 4 poles and 4 positions or less. This is the finished receiver, by the way. Well, finished for the time being – until I decide I just have to modify something –

Some more views of the underside of the finished receiver. You’ll notice that I designed a rear panel too. That also came from Front Panel Express – a more detailed view of it is coming later. The speaker is an 8 ohm, 4 inch, 6 watt unit made by CUI, model # GF1004. I got it from Digi-Key, part # GF1004-ND. Before finding this speaker, I purchased one from a company well-known for supplying vintage radio parts. It turned out to be very lightweight, with a small magnet, and generally rather disappointing. I liked the speaker I used in The Sproutie, so got the 4″ version of that one instead (the one in my Sproutie is a 3″ version). The aluminum speaker grille was custom cut by speakerworks.com

Coils were constructed in the same fashion as the coils for The Sproutie. In fact, the pinouts used on the octal socket are the same, so my Sproutie coils work in the Sproutie MK II, though they cover a wider range, due to the greater maximum capacitance of the tuning capacitor I used – a 2 x 50pF instead of the 2 x 35pF used in the original Sproutie. I decided to wind a complete set of new coils for this receiver. As of writing this post, I have 6 coils wound with a few more to go, as needs and desires dictate.

With The Sproutie, I used nylon hardware to secure the larger T68-6 toroids for the lower frequency bands. On the higher frequency bands, I used T50-7 toroids, and secured them with hot glue. This time around, I found that hot glue worked perfectly well for securing the T68-6 toroid cores too, so I used that technique exclusively. It’s faster and easier than using nylon nuts, washers and bolts. I didn’t think it would be the case, but if you need to re-make a coil, you can peel/break the glue off and re-use a tube base. In fact both the coils in the photos below were made with bases that were used at least once before –

I like these ceramic bases, because they are just a little higher than the phenolic ones, offering a bit more protection to the toroid. Wherever you get yours from, if they’re ceramic, they may well be the same ones as these, as most of these bases and sockets seem to be made in China these days –

“Take us to your leader”

You’ll need to figure out the exact details of your coils with the help of online calculators (I like the ones on W8DIZ’ site) and good old trial and error, but here are my details – they should give you a start. Remember to take into account the values of main and fine tuning capacitors, if they are different from mine – and the value of that 39pF capacitor between the tank and the base of the oscillator transistor, if you try a different value. I’ll update this table as I wind more coils. The plan is to wind general coverage coils up to about 21MHz or so, and a few more coils for specific bands. It is much easier, with the aid of the dial calibration graphs, to pinpoint exactly which 5KHz channel you are on, when the band coverage is limited to 1MHz or less.¬†With the 20:1 reduction ratio of this National HRO drive, and the large, relatively massive dial, I found it quite easy to tune in stations even on the 13500-18300KHz coil, which spans almost 5MHz. For pinpointing which 5KHz “channel” I am on though, a general coverage receiver to listen to the oscillator of The Sproutie is more reliable (and faster) than reading dial calibration graphs.

For dial calibration, I use a piece of freeware called Graph. You won’t be able to read the following graph, as it’s a bit small. The original is a bit larger, and the software has an option for zooming in on a particular area of the graph. This is the dial calibration graph (so far) for my 5475-8450KHz coil –

I guess it’s time to do a reveal and show you what this little feller looks like from the front. You wouldn’t think it, but I spent a great deal of time on the front panel, figuring out the exact placement of all controls, placement of the lettering, and fonts. I was looking for a specific type of vintage knob for the RF gain, filter, and AF gain controls, but didn’t find any in good condition while building the receiver. Then I found some knobs on clearance at my local Radio Shack. Those are brand new RS knobs, but I think they look good and fit in well with everything else on the front panel. My main concern was to not “overdo it”. When sitting at the computer with the Front Panel Designer software running, it’s quite tempting to go overboard on the lettering, or try a colored panel, and colored letters in a fancy font. Just because you can do something though, doesn’t mean you should, and I wanted a front panel that was understated, functional, and that would still look good, regardless of how my personal aesthetic might change. Minimalism is the key, though the one extravagance I did allow myself was the larger “Sproutie MK II” declaration, and my callsign. I did try my callsign in red but decided that it looked gaudy. Best to play it safe, I think. I was also concerned that the finish might be a bit too shiny or glossy, but it turned out to be matt with a slight sheen. I’m very happy with how this looks –

Although the regen and fine tuning knobs, and escutcheon plates look the same, the ones on the right are attached to a National “Velvet Vernier” 5:1 reduction drive, via a fairly long coupling shaft. The knob on the left is connected to the 10-turn regen pot (via a 3/16″ to 1/4″ shaft coupler), while the black escutcheon plate is spaced away from the front panel by washers, and attached to it in a fixed position with 4-40 hardware –

Here’s The Sproutie MK II with her little sister, for size comparison –

A quick word about that regen control. On first installing the main RF board, one filter, and the AF amp into the chassis, I noticed that occasionally, when receiving a strong carrier, I’d hear a ringing in the speaker. My first thought was that it was microphonics caused by physical feedback between the internal speaker, which was bolted to the chassis, and some part of the circuit. Plugging in headphones didn’t cause it to go away, however. Undeterred, I continued building, and it was only after finishing the whole receiver, that I realized what was going on. I discovered that if I hear a ringing, all I have to do it back off the regeneration control a bit, and it disappears. I think this ringing is due to the high Q of the circuit when set right at the threshold of oscillation. If you recall Dan N7VE’s presentation on filters that I referenced earlier, he talks about how ringing in filters is caused by abrupt phase changes at the edges of the passband. The cure, when designing them, is to limit the Q in any one stage. Similarly, if you experience ringing in your regen, backing away from the critical threshold of oscillation will lower the Q of the circuit, and should solve the problem. Fascinating. I’ll be interested to hear if any other regen operators have experienced this. My guess is this would be less likely to happen in a regen that utilizes a bipolar transistor for the detector (or combined oscillator/detector if it’s just one device, unlike this design).

I had to try a shot from a lower angle, for that authoritative look. When I’m spinning that big old dial and listening to CW, I can almost kid myself that I’m intercepting enemy broadcasts for the valiant code-breakers at Bletchley Park. ¬†In reality, I’m usually just listening to some ham tell some other ham what the weather is like at his QTH! –

The rear panel (thanks again, Front Panel Express) –

I like this receiver as it is, with the partially open chassis. From using The Sproutie, I have become used to seeing the vanes of the variable capacitor rotate as I tune the band, and I like that. I like seeing these vintage radio parts in action. However, I did learn from The Sproutie that whatever isn’t covered picks up dust – and when you’re living with 3 cats, 2 of whom are long-haired, a lot of cat hair too. I designed this receiver so that it would fit any standard 19″ enclosure that is also 6RU (rack units) or more high. The first plan was to make use of a hack (as the kids call it) of an IKEA product to make a low-cost rack cabinet. The IKEA Rast nightstand¬†is the right size, and only costs US$14.99. For that, and the cost of a pair of rack strips, you can have a rack cabinet that is either 6RU or 8RU high, depending on how you construct it. A Google search on “IKEA Rast rack cabinet” or similar will yield a lot of sites and info on how to do this useful mod.

That was my plan for this receiver until I came across nice-racks.com. ¬†David Tatelbaum makes beautiful studio racks out of his workshop in Massachusetts. He uses furniture-grade pine, though he will use other woods if you request them. The mahogany racks look gorgeous (but they do cost a bit more, of course). From his website –

“Nice-Racks are constructed of solid Pine¬†furniture-grade panels…not just pressed wood or¬†particle¬†board¬†covered in a laminate like some studio racks, but 100% real wood. The panels are cut to size and the components joined together securely using pocket-hole construction and self-tapping pocket-hole screws. The front sides and top edges are rounded, then the racks are sanded and stained. The finish is a clear matte enamel, scuff sanded between coats, to preserve the look and feel of real wood. Finally, hardware is installed and the fully assembled rack is boxed up and shipped out to its new home.”

After finding his site, I was hooked. ¬†Yes, it was going to cost more than the cheap IKEA hack but at some point during the design and construction of this regen, I decided that I wanted it to look really nice, and expense was going to be a secondary concern. I was going full-hog on this. Besides, it took me over 6 months to plan and put together and spreading the cost over that time, the cost per month for my hobby was actually quite reasonable – especially if I take into account all those movies and dinners I didn’t go to because I was at home building! Incidentally, David’s racks are most definitely not expensive. When you consider the cost of your standard rack cabinet – the ones you find in music stores that are made of heavy particle board and covered in black veneer, his racks compare in price very favorably – and they are vastly nicer. They’re not ideal for the rough life of touring but for a home studio, they are perfect – and very good-looking.

OK, so time for the big reveal. This rack cabinet makes The Sproutie MK II look so great –

David also fitted rack rails to the top half of the cabinet at the rear, and supplied a 3RU-high steel panel to help enclose the receiver, and hopefully keep the cat hair away. On the left interior side you can see the recesses for the self-tapping pocket-hole screws that hold the whole cabinet together –

And in case anyone ever wonders who made this fantastic cabinet for my regen, David left his mark. What a quality job! –

The National HRO gear box does have a small amount of backlash – even when I apply as much tension to the anti-backlash gear as my poor little fingers can manage. At first, the backlash was something like 1 – 1 1/2 dial divisions. After increasing the tension on the anti-backlash gear as much as I could reasonably easily manage without the use of tools, the backlash, though still there, decreased to about 1/2 a dial division. It is a small amount, and also predictable, so not really a problem. For the purposes of dial calibration, I always turn the dial in the direction of increasing frequency before taking a dial reading. This ensures consistency in the readings.

Some videos of The Sproutie MK II in action. In the first one, the ¬†towels are on top because Sproutie, my 3 1/2 year-old kitty (aka Sprat The QRP Cat) likes to sit on top of it, and I don’t want her claws to do to the wood what they have already done to my leather sofa –

The Sproutie MK II on 49M, 41M and 40M (though mainly 49M) –

There are some more videos of the Sproutie MK II, showing how a regen can be used in exalted carrier mode to enhance reception of weak AM stations, and on the 25M band, in this slightly more recent post.

There are a couple of things about my Sproutie MK II build that I’d like to change. The first is that, especially at the higher frequencies, the set is slightly sensitive to physical shock. A knock on the cabinet will shift the frequency slightly. I don’t recall noticing this effect with the original Sproutie, although to be fair, I didn’t do as much listening to SSB and CW with it as I do with the new receiver. I think one reason for this slight frequency shift may be the fact that the thick wires connecting the 2 stators of the main tuning capacitor to the coil socket are longer than in the original Sproutie. Although the effect is only slight, it is there, and that bugs me. It may also have to do with the much larger chassis, meaning more metal in the vicinity of a tuned circuit, that flexes when a physical shock is applied. The more I think about it, the more I think this second factor is the main reason. In practice, it is not a problem, but it is there, and I’d like to reduce it, if not eliminate it completely. Fixing a bottom plate to the chassis may help in this regard.¬†Incidentally, banging the desk on which the Sproutie MK II is sitting has no effect. The rubber feet probably help a lot.

The above phenomenon is responsible for an interesting ringing effect that happens occasionally when the regen is set close to the critical point for receiving AM. It only happens with the internal speaker, so is being caused by sound from the speaker vibrating the main chassis. I did mount the internal speaker on small grommets, but this didn’t cure the issue. I have been looking for a reason to purchase a Palstar SP-30B external speaker, and this may be it! This is what the ringing effect sounds like –

The second thing is that, because the cabinet is wood, the receiver is not completely shielded. This would be useful were I to wind a coil for the 2-3MHz region and use The Sproutie MK II in conjunction with crystal-controlled converters to cover specific bands. This is a Regenorodyne approach, like Gary WD4NKA’s inspiring Regenerodyne receiver here.¬†It would also be nice to reduce the possibility of picking up very local QRM in the shack. I could achieve better shielding with my Sproutie MK II by either simply housing it in an all-metal rack cabinet, or by cladding the interior of the existing wooden rack cabinet with thin metal plate or mesh. There is absolutely no hand-capacitance effect when using the set, due to the metal front panel, but when my cat Sprout jumps up on top of it (as she often does) the frequency shifts by about 20Hz. This is also due to the lack of shielding on top of the set. Again, it is not much, but it is there.

Sproutie (aka Sprat The QRP Cat) and The Sproutie MK II. Her contribution to the dial calibration of this receiver was carefully knocking the plug-in coils off the top of the receiver and watching them hit the floor.

August 14, 2015

A Sproutie is Born in France, to Henri F6GMQ!

Filed under: Amateur Radio,Ham Radio — AA7EE @ 12:10 pm
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Around the same time I heard from Andy M6YAO that he had finished his Sproutie, I heard from Henri F6GMQ, who was also building a Sproutie and close to completion. A Sproutie in Orsay, in the North of France – how inspiring! To my knowledge, there are now 3 Sprouties in existence – Henri and Andy came in joint second.

Henri built his regen in an old measuring instrument case. He kept the original 12V power supply, for powering the circuit. The variable capacitor came from an old tube radio. He’s already thinking of constructing a second one, in a nice wood or aluminum enclosure. Love those instrument handles!

A view from the back, showing the side braces that help to make the structure more solid. We must be thinking alike Henri, as my most recent version of The Sproutie also has instrument handles and side braces –

Henri’s first coil gives coverage from 5.5 – 7.2MHz. He says he has been able to listen to SSB, CW and broadcast stations and that selectivity and sensitivity are great, considering the relative simplicity of the circuit –

It’s interesting to see how other people build things. It looks as if Henri made his own Manhattan pads. Nice job! He also mentioned that he likes the AF stages of this receiver. Our thanks go to Charles Kitchin N1TEV for that, as they are the AF stages from the regen he described in the Feb 2010 issue of CQ magazine. Henri said that the receiver behaves exactly as I described. I do try to accurately reflect my experiences, so thank you for mentioning that Henri. I don’t think there’s any point in covering things up. If I think there’s a potential issue, I’ll mention it so you, the reader, will know what to expect.

Henri is looking for ideas for a simple 40M VFO, as 40M is his favorite band. He is thinking of building a high performance receiver for 40. If anyone has any ideas, you can leave comments underneath so that Henri will see them. He’ll be very grateful, and interested in all ideas, I’m sure.

Thank you very much for sending your photos Henri. It’s really great seeing how others build things, and it’s really great to know that there are now Sprouties in the US, the UK, and also France. Also, a big thank you to all who were involved in designing the circuit elements that make up this cool little receiver.¬†They include (but are not limited to) GI3XZM, GM4HTU, G3RJT, G3VMU, G4RGN, VK2BHT, G3RJV, and N1TEV.

August 8, 2015

Andy M6YAO Builds A Sproutie!

Andy and I have been communicating via e-mail since April. He is M6YAO now but back in April, he was plain old unlicensed Andy, who was about to apply for his Foundation License in the UK. He had built a Mark regen from Walford Electronics, which seems to have given him a taste for regens. He mentioned that it was a good receiver and worked well but that the tuning, accomplished by a polyvaricon with no reduction drive, was a bit critical, so he was looking for a regen to build that represented “the next step”, so to speak. It turned out that The Sproutie was that next regen for him.

I haven’t built any of the currently available regen kits but The Mark from Walford Electronics, and The Scout from QRPKits both strike me as good ones for anyone who has never built a regen, and wants to get their feet wet. However, when you’re ready for more, there’s nothing like a quality air-spaced variable capacitor and a nice solid reduction drive with calibrated dial to make you feel like you’re navigating the airwaves in style. In my secret (and perfect) world, there is a kit version of a regen with a pre-drilled and engraved, large and stout aluminum chassis, top quality air-spaced variable capacitors and reduction drives, and a variety of accessories (wooden enclosure, extra formers for adding bands, etc). Also, in my perfect world, this kit wouldn’t cost the many hundreds of dollars it would need to in the real world we all live in. If anyone were admirably eccentric enough to produce such a kit, I think that very few would actually buy it, due to the high cost.

Andy and I continued to e-mail each other, as his Sproutie gradually took shape. It was really interesting viewing the progression of his project as he encountered challenges, experienced setbacks, asked questions and one by one, solved his problems. It was a process that all home-brewers will recognize from their own pursuits, and a pleasure to observe. We have all had the kind of projects that present issues we are unable (or unwilling) to solve, so it is a fantastic feeling of achievement when projects succeed despite the obstacles that occur along the way. I get as much of a kick out of others’ successes as from my own – especially when it’s with a receiver like The Sproutie that is rather dear to me.

Incidentally, in the UK, when upgrading from a Foundation to an Intermediate license, there is a practical element to the requirements. Andy wanted to use his build of The Sproutie to qualify. The RSGB website says, “First, a practical skills assessment is taken which demonstrates your competence in basic electronics. This involves soldering a rudimentary circuit together using some of the components you learned about on the course.” A successful Sproutie build would seem to more than fulfill these requirements.

Bit by bit, Andy sourced the parts from various sources, including some from the US. He ended up with more reduction drives than he needed, and had to decide which one to use. He also incorporated a DC ripple filter from VE7BPO’s blog (I’m not sure if that became part of his final build). As the receiver slowly began to take shape, he was still deciding what to use for an enclosure. Whenever we build something, we make multiple decisions along the way, and it was interesting to follow along as Andy went through this process. I’m not sure if he experienced this, but I sometimes find that the plethora of decisions to be made really slows me down. Planning a project is a bit like playing a game of chess, as a decision you make now will affect many other moves in the future.

Although the AF amp board worked, on connecting all the boards together for the first power-up of the complete receiver, Andy was greeted by – a big nothing. We’ve all been through that and it can be somewhat dispiriting, but this is where our valiant builder’s homebrew mojo really kicked in, and he earned his stripes. He checked a lot of things, which all seemed to be in order, but didn’t give up. Finally, one afternoon, I received an e-mail that was titled “Eureka moment”. It turned out that his RF board was connected to the +ve supply line, but not to the ground. This is one of those “How on earth did I miss that?” moments that anyone who has ever built anything will know all about. Andy did experience a few more issues as he cased the set up but as they arose, he dealt with them. He said, ” I have learnt lots and I think it will help me in other projects I undertake in the future. ”

He used a metal file case for an enclosure, and the main tuning dial and drive is a NOS (New Old Stock) Muirhead Type C, with a 50:1 reduction ratio. 50:1 is huge – you must have fantastic slow tuning Andy –

Andy reports that it works well, fills the room with sound, and the bass boost works too. Because the file cabinet has a lid with a latch, he stores the unused coils inside the lid, held by spring tool clips. The plate on the top will have a legend, indicating the frequency ranges that the various coils cover –

Andy also owned a Tecsun PL-880 but he says that compared to The Sproutie, it seemed sterile. He writes, “The Sproutie seems to live and breathe in comparison and requires user interaction instead of just punching in a number through a keypad. ” He recently sold the Tecsun because, in his opinion, although it was probably technically better, it didn’t provide the same user experience as his new regen. A convert! This is exactly how I feel about direct conversion receivers and (particularly) regens. The simple circuit architecture leads to a relatively unprocessed sound and makes me feel as if I’m in more direct contact with the airwaves (or perhaps it’s just the lack of AGC!) It’s very affirming to hear the same sentiment voiced by someone who¬†is a relative newcomer to these intriguing receivers.

Andy will be taking the exam in October to upgrade from his Foundation license to an Intermediate license. He already submitted his Sproutie build as the “simple” radio project part of his exam and of course, it passed.

Congratulations Andy, and thank you for sharing your Sproutie build with us!

April 3, 2015

An Early Morning Spin On 49M With The Sproutie

This morning, my 2 eldest kitties did a real number on me. The senior was the first. At about 5am, she sat on her food shelf (one of 3 shelves mounted on the wall next to my bed, specifically for the cats to hang out on), next to her empty food bowl and began meowing loudly, while fixing me with an innocent gaze. I was able to ignore this for a good 20 minutes until the next eldest, my blind cat Jingles, jumped up on the bed and also began a “feed me” campaign, which consisted of vigorously rubbing her little furry head against my face. The combined effect of both initiatives was too much to easily ignore so as soon as I had fed them, I found myself sitting in front of The Sproutie and thinking that I might as well make use of the fact that I was up at 5:30am, while night-time and grey-line propagation on 49M would be in full swing.

The choice of 49M for this listening session was simply because it was the coil that was plugged in. I listen to Radio Habana Cuba most nights on 6165 and 6100KHz. The 6165KHz signal, which comes online at 6pm local (0100z) has been rather weak recently, but the signal on 6100KHz from 10pm-midnite (0500-0700z) is a powerhouse. I sometimes record the 6100KHz signal but am quite often foiled in my attempts to catch the penultimate hour of programming, due to RHC’s various foibles. Last night, the carrier appeared on 6100KHz at 4 mins after the hour, followed a further 5 mins later by the audio. My plans to record the 1-hour program in English were thus foiled and by the time it was repeated at 11pm local, I was feeling too sleepy to last the whole hour.

When going to bed, I usually leave The Sproutie on 6100KHz so that I can awake to the sounds of KCBS Pyongyang on the same frequency. It is mainly music, with occasional spoken word in Korean. I hear many of the same tunes during their morning programming, and there is great theater of the mind in hearing their slightly kitschy melodies interspersed with the¬†impassioned-sounding¬†commentary in Korean. I hear the same melodies most mornings, and there is a certain appeal to this somewhat exotic “sameness”. I can imagine the members of the elite in Pyongyang waking up to this kind of “inspirational” programming every morning.

Coffee at the ready, I decided to perform a band scan on 49M with The Sproutie. The idea was to log every station I could hear on the band. The excellent site short-wave.info made it possible to quickly ID most stations, before moving on to the next. I didn’t linger for too long on any one frequency, as the goal was to get an overall idea of band activity, rather than to positively ID every single station heard.

Needless to say, I heard a lot of Chinese ūüôā ¬†Here’s what The Sproutie and I came up with –

 Freq  Station  Language  UTC
 5830  WTWW  English  1342
 5875  BBC  English  1343
 5915  CRI  Mongolian  1347
 5925  CNR 5  Chinese
 5935  PBS_Xizang  Chinese
 5955  CRI  English  1354
 5975  CNR 8  Korean  1356
 5990  PBS_Qinghai  Tibetan  1358
¬†6015 ¬†North_Korean_Jamming¬†with un-ID’ed station underneath ¬†1401
 6030  CNR 1  Chinese  1404
 6055  Radio Nikkei  Japanese  1405
 6065  CNR 2  Chinese  1406
 6080  CNR 1  Music  1414
 6095  KBS World Radio  English  1415
 6100  KCBS Pyongyang  Korean  1417
 6105  Radio Taiwan International (jammed, but jamming not heard)  Chinese  1418
 6110  PBS Xizang  Tibetan  1420
 6125  CNR 1  Chinese  1422
 6135  North Korean Jamming (w/ music underneath)  1424
 6155  CNR 2  Chinese  1427
 6175  CNR 1  Chinese  1429
 6185  Unidentified station (possibly China Huayi BC. Corp  Music  1431
 6190  PBS Xinjiang  Mongolian
 6195  BBC (jammed, but jamming not heard)  English  1434
 6200  PBS Xizang (or Voice Of Jinling)  Chinese  1436
 6250  North Korean Jamming  1438
 6280  Xi Wang Zhi Sheng (just 100 watts!)  Chinese  1440
 6348  North_Korean_Jamming_with_station_underneath_(presumably_Echo_Of_Hope)  1447

Lots of stations – and loud too, For the majority of the listening session, I had the RF gain on the little Sproutie cranked down to 1/2 or 1 on a 1-10 scale. Another benefit of this band-scan was that I got to fill in a few more calibration points on the dial calibration graph for this coil. The details on this screen grab are a little hard to read but that’s fine, as your calibration graph would be different anyway. Just take a gander at that nice smooth curve though –

Anyway, that’s it. It is now about 9:30am and I am beginning to wish I hadn’t risen so early. However, I blame the cats, and the good side is that I got to take a whirl on 49M before first light. Don’t let anyone tell you that you can’t use a regenerative receiver for serious SWL’ing. If anyone says that their regen doesn’t cut it for SWL’ing, just tell them that it must be because they didn’t build it properly ūüôā

The Sproutie and a cuppa coffee kept me company early this morning throughout my sojourn on 49M.

February 26, 2015

A Popcorn QRP Regen Receiver and Lots More Air-Spaced Variable Capacitors

Many of us in the home-brewer community were really disappointed when Todd VE7BPO recently discontinued his popular and very through-provoking site “The QRP/SWL Homebuilder”. An archive of the site is available for download in pdf form and is a great resource. Though not quite the same as having the site, it’s great to have a copy of it for reference. Todd was having some issues with the site. He didn’t take it down due to lack of enthusiasm on his part and by way of proof, he’s back in style, with the new “Popcorn QRP – Scratch Homebrew Component-Level Radio Electronics” blog. It’s great – just like having his old site back. Todd combines circuit analysis and a theoretical approach with a strong leaning towards practical circuits that can be built by the home experimenter. Economy of design and performance are both considered, and from reading the accounts of Todd’s exploits, one suspects he is having a complete blast. If you haven’t visited Todd’s current blog or his previous site before, please note that the intent isn’t to provide the home-builder with complete step-by-step instructions on how to build a series of projects. This is circuit-level stuff, but if you’ve had a little experience at building circuits from schematics, all the circuits presented are tried and tested by our faithful protagonist, VE7BPO aka retired Professor Vasily Ivanenko.

All this is leading up to something, and that something is that our intrepid experimenter recently announced he had been revisiting the subject of regenerative receivers. He had built 4,¬†and was sharing one of them with us on his blog. Happy, happy, joy, joy! Even better, this circuit was the same basic topology that I used in The Sproutie – a ¬†circuit that separated the Q-multiplier and detector into separate stages. It’s an arrangement that is well-behaved and performs well. The regen control, a resisitive component, exhibits no hysteresis, and the addition of an RF preamp means that the circuit doesn’t suffer from common mode hum. If you build it well, it will be frequency-stable too, but that part is up to you ūüôā

The blog-post is here. It is based on the regen circuit published by Makota 7N3WVM, whose website is a treasure trove of circuits for the home builder. You’ll notice great similarity to the circuit of Nicky’s TRF that first appeared in SPRAT Issue 70 in 1992, and N1BYT’s WBR from QST Aug 2001. What’s really interesting though, is that Mr Ivanenko has added a bipolar transistor (a 2N4401) to the J310 FET infinite impedance detector, to turn it into a hycas (hybrid cascode) pair in order to increase the level of audio from the detector, as well as the reverse isolation, which can never hurt, right? Great idea! His circuit includes a bipolar RF preamp in common base mode to add isolation of the oscillator from the antenna, as well as a little bit of gain, and a 2-transistor preamp after the detector that he has used in other “popcorn” designs. He also makes his argument for continued use of the LM386 as a final audio amp in this post. The description in the 2nd paragraph, of the folklore surrounding regens is mirth-inducing – and spot-on.

I know that at least a few builders are considering making their own Sproutie and if you are still at the planning stage, you might want to think about Todd’s version of the front end. I haven’t tried it (yet) but Todd ain’t no slouch ūüôā ¬†If I were to incorporate it into my next regen build, my current thinking is to use his front end, and feed it into a one-stage active audio filter using a 5532 op-amp or similar, and then into a nice, low-noise LM380 with it’s fixed amount of 34dB gain. If I ever do this, I can promise you two things –

a) it will be many months, maybe even a year before I do it, because I am very slow at these things and

b) I’ll show you the circuit of my AF stages so you can join it up with Todd’s (ahem, I mean Vasily Ivanenko’s) front end circuit

 

Todd just revealed 2 encouraging pieces of news –

a) He just ordered some black and red chicken-head knobs for his next project and

b) He has decided to spend another 2 weeks working on regens

If you don’t already follow Popcorn QRP, it’s well worth adding to your RSS reader, bookmarks bar or similar.

 

The rest of this post may be a little annoying to those who have limited bandwidth connections, though I imagine anyone who is still surfing the internet on a dial-up connection or a very slow mobile connection learned long ago not to come here ūüôā I recently acquired some more air-spaced variable capacitors and I’d like to share some photos of them with you for no other reason than short-term visual gratification! As always, my preferred brand is Hammarlund. Not only are they of high quality, but I happen to like the way they look as well. They are drop-dead gorgeous.

I’ll start with a piece that was acquired a few months earlier, before the current flurry of buying activity. This is an MCD-50-M and may well end up as the main tuning capacitor of my next regen, unless I happen to find another MCD-35-MX like the one that was used for tuning The Sproutie. MCD means that is is a double-ganged unit (unlike the single-ganged MC units), 50 is the maximum capacity of each section, and the M at the end refers to the fact that the offset rotor plates give it a “midline” capacity characteristic, keeping the rotation vs frequency characteristic reasonably linear. Nickel-plated brass vanes for a good temperature coefficient, and all mounted on a high-Q ceramic base. Perfection! Look at those bright and shining never-been-soldered-to-before terminals –

Leaping forward in time to a couple of weeks ago, this MC-200-M “midget condenser” came into my life sporting an older original box, in almost as good condition as the capacitor itself. I love the graphic design on these older boxes –

Then came my haul of just a few days ago. I bought them all from the same seller. The boxes are a bit beaten up, but the capacitors are in great condition. First off, here’s the group shot-

Among them were two of these HFA-100-A’s. If you’re as picky as I am, these are not ideal for maximum stability in a VFO or receiver tuning control, as the vanes are only supported at one end. It would be fine as an antenna trimmer where it’s placed in series with the antenna lead, or as a reaction control, in a regen where a variable capacitor is used for this function. I’m not sure what material the vanes are made of in these parts –

In the same vein (vane?), I also scored an HF140. What a great part. It offers two methods of mounting. If I possibly could, I’d use both of them for maximum stability. This variable cap could be mounted underneath a chassis so that the nut on the threaded shaft helps to hold the front panel to the chassis, while the mounting bracket was screwed to the underside of the main chassis for extra rigidity. Rigidity is a very good thing with regens ūüôā –

An MCD-100-M (2 x 100pF). ¬†Nickel-plated brass vanes, a ceramic base (steatite actually), regular plate-spacing, and a “midline” capacity characteristic . Such a beautiful part. What else can I say? The US was once a manufacturing powerhouse –

Also in the haul were 3 x MC-20-S. I used one of these (from another buy) as the fine tuning control in The Sproutie –

Lastly, here’s an MC-50-MX. Single gang with capacitance swing of 10.5 – 53pF, midline capacity characteristic (for reasonably linear rotation-frequency relationship) and extra-wide plate spacing. This would be great for a VFO –

 

I also very recently acquired this National gear drive with 3 x 250pF variable capacitor attached. My relative lack of knowledge on National products caused me to misjudge. I discovered when it arrived, that the gearbox is a later model that is smaller than the older “classic” National gearbox drives. Also, it doesn’t have an eccentric bushing for driving the micrometer-style dial. I read somewhere that National stopped using the classic dial in their receivers in response to upgraded mil-specs that negated it’s use. It’s in good condition and turns freely, though the grease is old and it would probably benefit from a cleaning and re-greasing. I may well put this one up for sale –

There’s a little bit of surface dust on the plates and shaft but otherwise, it’s clean, and those terminals have never been soldered to. Amazing! –

No cracks in the insulators –

There’s only one detail that would require some attention from a builder, and that is that it looks as if the underside received a thwack at some point – either that, or it’s a manufacturing defect. One of the mounting holes is distorted and would need re-drilling and re-tapping if it is to be used. I think this is a solvable issue –

Another view showing this issue –

Old grease on the gears. If I were to use this, I’d want to clean out and re-lubricate, but that’s par for the course with these old yet still very serviceable gearboxes –

 

That’s it for now. Hope you didn’t mind me sharing all these pictures with you. As a parting thought, if you’re still planning to construct a regen and haven’t completely decided what to build, remember to take a look at VE7BPO’s Regen #4.

 

 

February 17, 2015

Extra Coils For The Sproutie Regen, With Coverage Up To 30MHz

Filed under: Amateur Radio,Broadcast Radio,Ham Radio,QRP — AA7EE @ 3:43 am
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Since completing The Sproutie Regen in it’s basic form in August of last year, I have been spending lots of time listening to it, and also some time winding coils for extra bands. On top of that, I wanted to add some extra thoughts and observations on building it and instead of creating a new blog-post every time I wound a new coil, or found something new (such as the fact that it seems to work quite well all the way up to 30MHz), I have chosen to add to the original blog-post. I have also been editing the post a little while adding new material, the point being to improve it and make it as informative as possible to anyone thinking of building it. Also, if I added a new blog-post for every new piece of information, then potential builders would find it harder to access all the info. This way, if you want to learn about, and maybe build The Sproutie, reading the one original post will always bring you up to date.

Since finishing The Sproutie, I have added coils for 2063 – 2670KHz, which covers the 120M BC band, 49M, 31M, 25M, 19M, 16M BC/17M ham, and an experimental coil that covers ~24-29MHz. The coil box is now full, and a picture of it has been added to the original post. I have also updated the coil tables to include full details. The experimental coil for 24-29MHz was wound out of interest, to see if this receiver would work passably at the higher HF frequencies and indeed, it does seem to. I copied SSB on 24M, as well as SSB ¬†and CW on 10M, and local CB’ers on 27MHz. (EDIT on 2/18/2015 – this afternoon, I copied 10M beacons from K5AB in Texas on 28280KHz and WA2DVU in NJ on 28257KHz) I added no padders or series caps to taylor the coverage to a specific band. I didn’t even add a link winding – plenty of RF was being coupled into the circuit from pin 7 of the octal base without it, though a finalized coil would probably include a small loop to couple as much RF as possible, withut overloading the detector or stopping the oscillator.

Blog posts aren’t much fun without photos so, although I just added this photo to the original post, here’s what my coil box looks like now that it’s full up with coils. ¬†If I wanted to add coils for specific ham bands, as well as the remaining BC bands above 16M (and the 22M band), I daresay I could fill another coil box!

The cigar box full of Sproutie coils. The unmarked one sitting above the 25M coil is experimental, and covers approx 24-29MHz.

If you’re getting a bit fed-up with me talking about this little receiver a full 6 months after I finished building it, take it as evidence that it’s a good ‘un. 6 months after building it, I still think that it was a very worthwhile project, and continue to derive much enjoyment from it. ¬†The sounds of Radio Habana, Cuba fill my apartment on many evenings, and on the same frequency (6100KHz), music from KCBS Pyongyang in the mornings, as well as Radio Australia are my main morning staples. I’ve heard Spanish numbers stations, air-traffic control, coastal stations, military communications, and all sorts of weird and wonderful bleeps and bloops that you expect to hear in the shortwave bands. Before I end this post, allow me to say just one more thing that I have said many, many times before. If you are going to build a regen, make sure you pay careful attention to the physical construction. There, I said it. I promise I won’t mention it again ūüôā

 

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 ūüôā

 

“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‚ÄĚ. 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!

November 23, 2014

Videos Of The Sproutie Regen In Action

Many apologies for taking so long to get these videos up. The only camera I have that can do video is so old and gives such poor quality video, that it’s a little tough for me to feel inspired in that direction. ¬†I do like to put quality still pictures on my blog, and am currently unable to do justice to my projects when it comes to videos. ¬†However, even a low-res video can still give you an idea of how a receiver handles that no amount of still pictures can, so last night and this morning, I made a few brief videos, and here they are. I would recommend viewing them on this page rather than on YouTube, simply because there is no point in seeing the larger version on YouTube – the video resolution simply isn’t there. Aaron N9SKN is building a Sproutie, and asked if and when I was going to post videos. His request gave me the final push/feeling of guilt that was needed to get me moving!

Here’s The Sproutie receiving CW and SSB on 20M (with the coil that tunes from 12100 – 14400KHz) –

and here it is receiving AM stations on the 60M and 49M BC bands (with the coil that tunes from 4810KHz – 6320Khz) –

As the main blog-post on The Sproutie shows, I have coils for continuous coverage from about 3MHz up to 16MHz (as well as a coil for 2.1 – 2.7 MHz) and have wound temporary coils that worked up to 24MHz. It will probably work even higher. I have even read reports of Nicky’s TRF (which is the circuit I used for The Sproutie’s front end) being used successfully on the 10M amateur band!

The original blog-post giving construction details of The Sproutie is here.

August 21, 2014

The Sproutie – A General Coverage Regen Receiver with Plug-In Coils

NOTE – Many thanks to Aaron N9SKN and Cliff WA9YXG, who pointed out errors in the schematics. They have been corrected, and N9SKN has built a working Sproutie 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 –

Ads like this for H.A.C. shortwave receiver kits were common in the UK up until the early 1980’s. Image taken, with permission, from Louis Meulstee at http://www.wftw.nl/

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.

The H.A.C. Model DX Mk. 2 cost me all of ¬£14.50 in the late 70’s. (Photo taken by Philip McNamara and taken, with permission from Louis Meulstee at http://www.wftw.nl/)

This one tube regen used an HL23D double diode triode tube with low current consumption 1.5V filament. The blue lead on the left leads to a connector that plugged into a 90V high tension battery. (Photo taken by Philip McNamara and taken, with permission from Louis Meulstee at http://www.wftw.nl/)

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), and 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” ūüôā 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 ūüôā ¬†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 –

The coil for the 16M BC and 17M ham bands. This one covers 17400 – 18200KHz.

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 ūüôā ¬†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 ūüôā

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 ūüôā

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.

Sprat The QRP Cat aka Sprout aka Sproutie, after whom this receiver is named.

Videos of The Sproutie in action are here.

Thoughts on using The Sproutie to receive SSB are here.

Sproutie is ever-curious, just like her regen namesake is always seeking out signals.

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 –

This cigar box cost $5 from a local tobacconist and makes an excellent coil box. The unmarked ceramic tube base sitting on top is the experimental coil for 24-29MHz. 4 adhesive vinyl bumpers stuck to the bottom help to protect it from rough surfaces.

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