Dave Richards AA7EE

April 12, 2015

New Solid State Regen Discussion Group

Filed under: Amateur Radio,homebrew radio — AA7EE @ 6:06 pm
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I had meant to tell you about the new online discussion group for regen builders in the last post, but it slipped my mind. Sometimes, when writing blog-posts, my big concern is to get it finished, so I can put it behind me and move on to the next new, interesting thing. In the midst of the push to do this, things sometimes get forgotten.

The bright side is that now, this subject gets it’s own post, and may get a little more attention as a result. Professor Vasily Ivanenko of Popcorn QRP fame, has started a new regen discussion group on Google+, designed specifically for discussion of solid state regens, You can find it here. Not too many members yet, but it’s very new. There’s a good discussion group on Yahoo Groups, called RegenRX, which tends towards discussion of tube designs (though solid state is discussed there also). I used to really enjoy Yahoo Groups, but have never been able to make peace with the newer interface. I think it’s less user friendly, and my visits are limited as a result. There is also discussion of regens, as well as other simple receivers, on The Radio Board, run by Dave Schmarder N2DS and Jim Kearman KR1S. ¬†It’s a discussion board with a classic and uncomplicated interface. Nice and clean looking, no drama, very agreeable, and full of good information and communication, as well as an attentive and dutiful moderator.

I tend not to participate a great deal in online discussion groups, preferring to make a few posts, then duck out and leave everyone else to it. However, I couldn’t resist joining this one. I hope you will too.

April 8, 2015

Holy Grail Attained – A National HRO NPW Gear Drive and Dial in FB Condition

Firstly, I must apologize for posting so many pictures of these National HRO gear drives and dials. Once I decided that a building a regen with one of these dials and drives as the centerpiece was a goal, it became something of a preoccupation to find both a dial and drive that were just right. Luckily, I have now found that perfect combination, and can promise that this will be the last post on the subject ūüôā

An idea that has been brewing in the back of my head was to write a post on the subject of dials and reduction drives. I have purchased and looked at a number of different types over the last year or so, found a few to be slightly lacking, and others to be eminently suitable, for the purpose of tuning a home-built radio receiver. For a number of reasons (that I may go into in a future post one day), I consider the National HRO micrometer dial and gear drive to be one of the best solutions. Luckily, there are still quite a few of them knocking around, for the builder who is willing to spend a little time looking for just the right one.

When I saw this particular drive on eBay, I knew I had to have it, at almost any price (within reason). Firstly, the gear drive was in nice physical condition. Also, it had a feature I had not seen before. Although I have been aware of these drives since my teenage years, I have only been paying close attention to them in the last few months. Perhaps this is not that unusual, but it stood out to me – there was an extra feature on the front of this drive, in the form of a shaft rotation limiter. It is an ingenious mechanical device that will not allow the dial to rotate more than 10 turns in either direction. The rignt-angle drives have end-stops built into the inside of the top cap of the gear box, but the standard straight-through models have no such rotational limits. ¬†The variable capacitor I have been planning to use with this next project does not have end stops, so to have one built-in to the drive would be great. The fact that this drive looked to be in really good condition as well (judging by the photos online) elevated it to “must have” status.

A week or two later, this little beauty was in my hands. These are the “before” pictures, so if you look at these, make sure to stick with me to the end of the post to see how things turned out. Having said that, it looked pretty darned good from the get-go though. Although you can’t really see how the shaft rotation limiter works, you can see it’s component parts that are stacked over each other on the tuning shaft, in between the metal end plate and the cast metal gear box –

On removing the top cap, I was expecting to see a moderate amount of partially dried grease on the various component parts of this drive. What I found instead was a large amount of grease, applied in generous dollops. I wonder if there had been a special directive to apply a lot of grease in order to protect this batch against an extreme climate, ot perhaps it was just down to the whimsy of the worker who had been applying the grease to these gearboxes?

Look at all that grease! You can’t see it. but there were some very large dollops underneath the gears, in the interior of the gearbox –

Before dousing the gearbox with WD-40 and then dish soap, I removed as much of the grease as possible with a toothpick, before partially disassembling it. Then I went to town on the gearbox and all the parts, with generous amounts of WD-40, a toothbrush, then dish soap and the toothbrush, followed by nice long soaks in warm dish-soapy water (and the toothbrush again). Then came a good rinse in non-soapy water, and plenty of attention from a hairdryer on the hot setting to dry it all out.

Look at the squeaky-clean result. It just amazed me, looking at this, to realize that it was something like 70 years old, and it has plenty of life left in it still –

All the parts were now clean, dry, and ready for reassembly. It is not my intent to give detailed how-to instructions here. If you read my previous posts about these drives, as well as the other supporting information online that I have linked to in the previous posts, you’ll know enough to figure things out – especially once you’ve looked at one in real life. ¬†Although these straight-through gearboxes have more parts than the right-angle drives, they are easier to figure out. In the following shot, you can see the slip-on washers of the shaft rotation limiter that fit over the tuning shaft. Each washer has a tab with a small protrusion that prevents it from slipping over the collar next to it. There are 11 of these tabbed washers in all –

The plastic lid under the loose parts once held fruit salad from Genova Delicatessen. If you visit Oakland, CA and like East coast style deli’s, Genova’s on Telegraph and 51st is a must!

Remember to set the anti-backlash setting on the gear that is spring-loaded, before inserting the tuning spindle into the gear box. Do not over-tension it, or there will be too much friction when tuning. All you need is just enough tension to counter the backlash and no more. The sprung gear only needs to be offset by one, or two cog-teeth at the most.

Next came the lubrication stage. There needs to be grease in every place where there is metal moving over metal. The shaft rotation limiter with it’s 11 tabbed washers added a fair bit of drag, even when coated with a thin film of grease, so I squibbed a small amount of turbine oil in between each washer. While doing this, I was wondering about mixing turbine oil in with the synthetic grease. So far, it has seemed to work fine. If there are any problems in the future, it would not be hard to remove just the front plate and the washers, so they can be cleaned and re-lubricated. At this point, I am almost looking for excuses to do things like that!

This is such a good-looking gear drive. I almost can’t believe that it is something like 70 years old. ¬†If you look closely at the 4 screws (of which you can see 3 in the following picture) holding the eccentric hub flange to the front plate, and compare with the very first picture in this blog, you’ll see that I have carefully filed them down. I did this in order to maximize clearance with the back of the micrometer dial. I am planning on using a 4mm front panel in my next regen, and need all the clearance I can get –

The dial that came with this particular drive was in good shape. However, I already had one that was in even nicer condition. This particular combination of dial and drive are the best in my small collection. They have made the cut, and with the 20:1 reduction ratio and nice heavy dial, will make a grand main tuning dial for a homebrew receiver –

April 7, 2015

The National HRO NPW Dial and Gear Drive

The gradual (and selective) acquisition of vintage radio parts here continues, as I hone in on the perfect tuning dial and drive for my next regen, I’ve been wanting to find a really nice National HRO Micrometer dial and drive for the purpose, and have finally found it. ¬†I had to purchase 4 dials and 3 drives to get exactly what I wanted though.

As well as selling their gear drives with built-in variable capacitors, National also sold the stand-alone PW and NPW drives which could, with the use of a shaft coupler, be used to drive any variable capacitor the builder desired. The PW drive, in which the drive shaft ran Parallel With the front panel, was also known as a right-angle drive, as the drive shaft came out of the gear box at right angles to the tuning shaft. The drive shaft of the NPW drive was Not Parallel With the front panel, and was also known as a straight-through drive, as the tuning shaft and drive shaft were in the same plane. For many builders, myself included, the PW drive is not ideal, as the variable capacitor would tend to get in the way of the other front panel controls and parts. On the other hand, with the NPW drive, the main tuning capacitor sits directly behind the gear drive, leaving room either side of it for the other front panel variable capacitors, potentiometers, switches etc. From the National Radio Products catalog for 1947 –

The NPW drive was my holy grail, and I set about watching eBay for one. The first such acquisition was listed thus,¬†“has¬†dings,scratches and scuffs – knob has spring and turns, gear turns properly”. The dial had definitely seen better days and although the gear box did look to be a little scuffed, I figured that it was most likely in good working order, and would only need a through cleaning and re-lubrication to put it in working shape for the next few decades. I paid a little more than I wanted to for it but darnit – I wanted it, and was pleasantly surprised when it arrived to find that it was in fair condition. I haven’t pictured the dial, because it was in pretty rough shape but that was of little concern, as I already had a very nice dial. It was the gearbox I was looking for. This one didn’t end up quite making the cut for my next regen, but it came close. These photos are the way it was on arrival, before I cleaned and lubricated it –

The grease was old and although the gears did turn smoothly, I couldn’t help wondering if they’d turn a little smoother with a complete cleaning and re-greasing. The grease was getting a bit dried up, and it was time for this gearbox to receive some TLC –

I wasn’t able to find as much online documentation on this gear drive as on the right-angle drive (the one that uses a worm gear). This makes sense, as the National HRO receivers used right-angle drives – there seem to be more of them floating around than these “straight-through” drives. The only place I found any info on the NPW drives was here. However, after disassembling and lubricating a right-angle drive, this one was easy to figure out. It has more moving parts, but is a very simple arrangement. You may not be able to figure it out from looking at these photos but if you see one in real life, after turning the shafts and seeing the gears turn, it’s operation becomes very clear –

You can’t see the eccentric nature of the hub too well in this picture. I probably didn’t capture it from exactly the correct angle. However, you can see that it had been removed and replaced upside down. Note how the word “top” is at the bottom. This was probably so that the gear drive could be positioned upside down in it’s previous installation (whatever that was) –

Time to take it apart, and thoroughly clean all the old grease off. This was achieved with an old toothbrush, many squibs of WD40, then a great deal of dish soap, scrubbing all the time with the toothbrush, before rinsing and drying. A hairdryer at maximum heat helped the drying process. It was surprising how hot the metal casting became after a minute or two under the hairdryer. Here’s the fully cleaned and dried gear box, before re-assembly, I didn’t remove the gear that was attached to the drive shaft, though this would have been quite easy –

Two closer views of the eccentric hub with the spindle and 2 fiber washers –

The cleaned and re-assembled gear box, before re-lubrication. It’s not too clear in this photo, but the gear on the right is tensioned with a spring to eliminate backlash. You can see the spiral spring near the center of the gear. When re-inserting the tuning spindle, you should use your fingers to tension the gear by just one or two teeth before engaging the tuning spindle. If you tension this gear too much, there will be too much resistance when you try to turn the tuning knob. All you want is enough tension to eliminate the backlash and no more –

A view of the cleaned gearbox from above. What a difference!

And the gearbox cleaned and assembled, but not lubricated (it will have to be partially disassembled in order to be lubricated) –

For lubrication, I use Mobil 1 synthetic grease, applied with a small (1 ml) pipette (the type used to administer medicines to pets), a toothpick and at times, my fingers. After applying sparingly, I turn the gears to distribute the grease and with the toothpick, remove any surplus. Once any grease has been pushed out of the gear teeth and to the side, it’s never coming back,so why keep it around? Grease should be applied in every place where metal moves in contact with metal, but you don’t need a lot. This includes the inside of the eccentric hub, through which the tuning spindle passes (the spindle that is connected to the dial), as well as the outer part of the hub, which comes into contact with the micrometer dial –

In the following view, the anti-backlash spring on the left-hand gear is visible. You can see one end of the spring poking through a hole in the gear, and the other end held in place by a collar around the spline –

Here’s a final view of the assembled and lubricated gearbox. I forgot to install the 4 screws on the top cap but other than that, it’s complete, and ready for many more years of service –

The dial that came with this gearbox has seen better days. Although I have certainly seen gear drives of this type in better external shape, this one does operate smoothly. ¬†You can spin the dial and it continues spinning for a turn or two, even with a variable capacitor attached. Not long after cleaning up this drive, I found another one in particularly nice condition, which will be the main tuning control for my next regen. I’ll ¬†show you that drive in the next post. In the meantime, this one will go on the shelf in a box, waiting for the right future project to come along.

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.

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