A complete digression.

Happy New Year.

Now that the holidays have passed and time has started to free up a bit, I’ve found my way back to the bench and started to resume experiments on a space charge tube regen, And while I actually have some interesting progress to report on that front, I’ve been sidetracked into completing a completely unrelated project by yet another random sequence of events.

This one started, as they often do, with an eBay purchase. I probably shouldn’t be telling you this, but I will sometimes bid on a lot of several crystals, if there are at least a few I can identify as being on useful ham frequencies. If the average price per crystal is attractive I’ll go for it.

Out of band FT-243’s are also useful because the holders can be filled with modern HC49/U or similar crystals. I sometimes find crystals at frequencies just below the ham bands. These can (in theory, I have never actually attempted it) be ground down to raise their frequencies a few hundred Hertz, to values that fall in-band.

Of course, I get a lot of fairly useless stuff as well. There may be a few interesting holders, or items that might have antique interest, but for the most part the rest is of no use and collects in a bin on a shelf in the basement.

This particular lot contained a curious item: a sealed detector crystal for a crystal receiver set.

The mysterious Philmore Fixed Crystal DETECTOR

The mysterious Philmore Fixed Crystal DETECTOR

These holders contained a hunk of galena and a cat’s whisker (short, stiff, wire probe) sitting on a “hot spot” on the galena, potted in a plastic holder to permanently secure the detecting action needed in a crystal set. This was a modern convenience compared to the tricky business of finding a “hot spot” that would detect. The really cool thing about these crystal receivers is that they produce audio with no additional input power. All the energy necessary to produce the audio is captured by the wire antenna.

It was a curious artifact, and I put it on a shelf on my operating desk, as a radio good luck talisman; but everytime I spied that crystal dector sitting on the desk, I wondered to myself whether it still worked. I would not have gotten much past the wondering stage were it not for the fact that I happen to have a pair of high-impedance headphones – a critical component in any crystal receiver experiment.

High Impedance Headphones

High Impedance Headphones

These phones were given to me by my elmer, W2WTV Gordon (sadly a silent key now for many years). I recall visiting him one Saturday while he was cleaning up in his shack, and him handing these phones to me, saying gruffly “Here take these, you might want to build a crystal radio someday.” I held on to them ever since, not knowing when if ever I would want to build a crystal radio, but they just seemed like something you shouldn’t part with, because they’d be difficult to get a hold of if the need ever arose. I measured the DC resistance of these to be about 2200 Ohms.

So almost against my will, I started to research crystal radio designs. Some of these babies can get very elaborate, after all at one point they were state of the art. There are dozens of designs out there, and I started to filter through them. Patterns began to emerge.

I decided on a variation of the simple “oatmeal box” receiver. Easy to build, it requires a big air wound transformer (hence the oatmeal box) connected to the antenna, a resistor, a variable capacitor, a diode detector, and high-impedance phones.

I was all set, I had all that stuff on hand. I decided to go a little uptown from the oatmeal box, and wound my coil on a piece of 2 inch PVC pipe. Also, I used one of those cheap, ecologically responsible bamboo cutting boards for a base. I think these things are great for any “bread board” project, the small ones cost about five dollars in the produce department of the local supermarket. Easy to drill, and good looking. What’s not to like?

This past weekend, I got to work. Not that there weren’t about twenty more pressing things I should have been doing, but by this point my curiousity about the detector was approaching obsession. First step: recompute the number of turns needed on my piece of pipe, by reverse engineering the oatmeal box design.

Using an online air wound coil calculator, I estimated the inductance of the oatmeal box secondary to be about 500 microHenries, and then calculated the number of turns I would need on the pipe for the same inductance. Using 28 AWG gauge wire, it worked out to be about 100 turns. Sitting down to binge watch old PBS shows, I started winding.

I won’t bore you with the details of winding the coil. I know a lot of guys don’t like winding toroids – this was far, far worse than any toroid. 28 gauge wire is impossible to handle. It was a nightmare. Finally I got the coil done, and measured the inductance. More than twice the calculated value. This thing wasn’t going to resonate any where near the AM broadcast band.

Re-purposing some nice 18 AWG gauge enameled copper wire liberated from my wife’s studio, I wound a second coil of 60 turns, tapped as indicated in the design. Much better experience all around. I don’t recommend using teeny wire for this kind of project.

Taking much more time than it should have, I laid out the components on the cutting board. I didn’t have the specified 47 kOhm resistor, so I used a 51 kOhm instead. Nothing about this design struck me as being all that critical, so I figured close was good enough. With everything wired up, I brought my creation up to the shack, and hooked to my antenna.

Attached to the antenna (new diode)

Attached to the antenna (new diode)

The antenna is a 135 foot doublet, fed with ladder line, with a bunch of stuff between the wire and the shack, like a big balun and an automatic tuner. But since rf does demonstrably get in through this pathway, I figured it might work for the crystal receiver. I hooked the center pin of th PL-259 connector to the top of my coil, and the shell to the ground side. Hooked up the phones, and spun the dial….

Profound silence.

I tried all the taps. No good.

Okay, back to the design docs.

Schematic for my version.

Schematic for my version.

After carefully reviewing the small schematic for the rig I realized I had flipped the sense of the secondary. Could phase matter? Well, just to be sure I switched two soldered connections, and now my construction exactly matched the schematic. Back to the shack, hooked up the alligator clips, and…. nada.

Okay, well it could be the phones – I had never tried them in any other circumstances. Or, it could be my antique crystal detector. I popped the old unit off, and stretched a brand new 1N34 diode across the posts. Connections hastily reconnected, tuned the cap on one tap, then the next… wait, what was that? Yes, faintly, distantly, but unmistakably – salsa music!

I ran downstairs and got my son to come up and listen. He put on the phones, concentrated for a moment, and said “Sounds like a Spanish language station?”

Yes! Success! A soft, vague whisper, but reception nevertheless! My receiver works, and the question answered: the antique crystal detector is a curio only, dead as a doornail.

A little further experimentation reveals that the phase of the coils does matter – switching the antenna and ground connections completely killed the signal. Playing with the receiver late in the evening, I was able to hear four or five distinct stations, but none as strong as my Spanish station, which turns out to be WEPN, ESPN Deportes on 1050 kHz AM in New York.

Switching between taps improves selectivity and reduces sensitivity as fewer turns are selected. I probably could get better reception with a good earth ground and a more direct connection to the wire, but those experiments will wait for some other time. For the time being, I am at peace with crystal radios.

Now about the space charge tube regen receiver. I have found an interesting design that I think will adapt nicely to space charge tubes, and I have prototyped the input RF amp with encouraging results. But this will be the subject of another post. Until then

73
de N2HTT

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A key repair.

Back at the beginning of November I happened to be in the local Barnes & Noble bookstore on a Sunday afternoon, when I noticed signage for the “Mini Maker Faire” event B&N was holding the following weekend. My initial reaction was: “not that interesting”. I had attended the big Maker Faire at the Hall of Science last year, it was fine, very focussed on 3D printing and robotic oriented stuff. For me, not worth a repeat visit.

But then, as I was leaving the store, I saw the phrase “signing up new presenters every day” on the announcement board. That piqued my interest: would they want a demonstration of a ham radio “maker” project?

Left to my own devices, I would have left the store still pondering this question, but for my wife’s prodding to go ask a manager. I did, and they were interested. In fact, the store personnel I spoke to mentioned that although they had reached out to local schools looking for presentations, they had gotten very little response. I got a call the following Monday from the store manager, made my pitch, and was put on the schedule for the following weekend.

The next thing to do was to reach out to my local radio club, PCARA, and see if there was any interest in participating in the presentation and supplying collateral material about Amateur Radio, and our club. I got an enthusiastic response, and checking back with the folks at B&N got permission to display and hand out ham radio materials – I thought this was pretty generous of them.

The project I had to demonstrate was a pretty good fit for a ham radio “maker” project.

DFR front panel

DFR front panel

Called the Digital Fist Recorder, it is an Arduino based device that records and plays back CW sent with a straight key, cootie key, or bug, exactly as sent – thus exactly reproducing the “fist” or sending style of operator.

DFR under the hood (arduino stack on left, keying circuit on right)

DFR under the hood (arduino stack on left, keying circuit on right)

I had written an article on the project for QST Magazine, which had just come out in the November issue, so the timing was perfect.

In the presentation (done at three sessions from Friday evening to Sunday afternoon), I touched on

  • some background on amateur radio
  • the history and use of morse code in radio
  • a demonstration of the DFR, complete with a key that audience members could try out
  • a discussion of the “maker” aspects of ham radio, showing kits and scratch built projects

The presentations went well, I gave out several handouts and lots of interest was generated.

CW Demonstration, B&N Maker Faire (photo by M. Pritchard, NM9J)

CW Demonstration, B&N Maker Faire (photo by M. Pritchard, NM9J)

As part of the demonstration, I knew I would have people wanting to try out the Morse code key, so part of my preparations included selecting a key that would stand up to being used by folks not familiar with the art of radio telegraphy. I have a lot of keys, and I am rather fond of all of them, so I put particular effort into selecting a key that would be robust enough to withstand any unintentional abuse. After much deliberation, I chose my D-117/K5 “Chinese Army Key”.

Chinese K5 key

Chinese K5 key

It is very heavy, solid steel with hard brass and steel contacts. While not my favorite for daily use, one gets the impression that you can bang the hell out of it without complaint.

It performed marvelously, survived without a scratch, and acquitted itself well in the hands of several young kids who learned to send their first names in Morse Code.
And it reminded me of another Chinese key that I own, one that I liked very much, that had met its demise at my own hand about three years ago.

The other key was a K4. This key was manufactured for the PLA in the 1960’s, and was readily available on eBay and at Morse Express for very reasonable prices. In recent years the original source of the surplus keys has dried up, but they are still made at the same plant in Changshu, and are still available today but at much higher prices.

The key featured a very heavy cast iron base, shrouded in a highly chromed steel jacket. A steel lever, supported by robust posts, pivoted on jeweled pivot bearings, and featured large silver contacts. It has a very good feel, and stayed put on the desk.

I liked this key so much that I was using it in the November CW Sweepstakes three years ago when, while rearranging things on the operating desk, I knocked it off. The key hit the ground lever first, and shattered the bakelite pedestal that supports the lever. I couldn’t bear to discard the parts, so I just put them away in a box at the time. Playing with the K5 made me nostalgic for the K4, checking current eBay prices for the key made me consider a repair job.

Examining the parts of the broken K-4, it was apparent that the breaks were clean and tight-fitting. Not too much shattered material had been lost in the break. The key was a likely candidate for a glue repair.

Broken bakelite pedestal

Broken bakelite pedestal

I wanted a glue that would have extremely high cured strength, and some ability to fill in the broken areas. A two-part epoxy seemed to me to be the most likely candidate.

The epoxy should have a very high cure strength, and since the key had been broken for three years, I didn’t think a rapid curing glue was needed. I went searching the adhesive department of our local Home Depot, pondering over the many two-part epoxies available, comparing cured strength, cure time and color to select the most appropriate.

As it turned out I didn’t find a slow cure epoxy that would work; the only one they had was opaque white in color, definitely not a good choice. Second runner-up was Gorilla Glue two-part epoxy, with a 5 minute cure time, which is clear and boasted the highest cured strength. The short cure time was not an advantage in this case, as it meant that all the positioning and clamping had to be done quickly.

On the same visit, while cruising the tools section, I found a new item that I can’t recommend highly enough – DeWalt now makes tiny trigger style clamps, for only about $5 each. These are perfect for clamping small repairs, and I picked up two to supplement the other small clamps in my armamentarium.

I knew that the success of the repair depended on absolute flatness of the glued bakelite block, and good end-to-end compression of the break while the glue set. To achieve this, I used clamps at 90 degrees to each other – two to hold the base flat, and one to compress the glue joint. I needed a flat surface to clamp to. As it turns out, I recently bought at a thrift store a picture frame fashioned from two thick blocks of plate-glass. I intend to use this for some crystal grinding experiments, but in the mean time it made the perfect support for the glue job.

Preparing to clamp glue job

Preparing to clamp glue job

To avoid the embarrassment of gluing my repaired bakelite part forever to the glass block, I covered the block in plastic cling wrap. I figured that even if the plastic wrap clung to the glued joint, it would be easy to pick off. Or at least easier to pick off than the thick glass block.

The last concern I had was the inevitable bit of glue that squeezes out of the joint and sits on the surface, creating a bead that follows the path of the break. A little research suggested that using acetone or mineral spirits once the join was clamped would remove the bead. I had acetone on hand, and am pleased to report that this trick worked perfectly.

The epoxy user's friend

The epoxy user’s friend

The procedure was:

  • wrap the glass block with clingy plastic
  • pre-position the broken bits and clamps
  • mix the glue and apply
  • clamp the joint – starting with one end of the piece down to the block, then all the parts together, then the other end to the block. This involved a little fiddling to get it all snug
  • with acetone on a paper towel, clean up the glue bead
  • leave the whole thing to think about it for at least 24 hours
Glue job at 23 hours 59 minutes... wait for it..

Glue job at 23 hours 59 minutes… wait for it..

That last step is the hardest, but you really need to allow the epoxy to rest undisturbed for a good while to reach full cure strength. Anyway, the key had been on the disabled list for three years, so what was the rush?

After the curing time was over, the bakelite base came off the block easily, and it was no problem to pick off the clingy plastic. I then re-assembed the key, and had to deal with the matter of the conical spring.

Unfortunately, the original conical spring was lost. Whether I lost track of it when the accident occurred, or it got away during captivity in storage is not clear, but it is definitely gone. A quick check of internet sources for conical springs shows that:

  • you can get any spring dimensions and springiness you want from spring suppliers
  • they won’t sell you less that 25 or so minimum order

Not wanting to invest that kind of money in a world class conical spring collection, I looked to other venues. Morse Express sells replacement springs for Nye-Viking keys; I ordered a couple and although they are very nice, they are much too small for the K4.

I then took a look on eBay for either springs, or busted keys with the springs still attached. I found an auction for three springs that were a bit larger. These turned out to be usable (it’s what you see in the photo), but I am keeping my eye out for other possibilities in the future.

The K4 key, after repair

The K4 key, after repair

All in all, the repair was a great success. The key handles just as it did before the disaster, and I’m really pleased to get it back in service.

73
de N2HTT

Posted in Arduino, Ham Radio | Tagged , , , , , , , , , , , , , | 1 Comment

New Wire

Almost exactly three years ago, super storm Sandy made landfall in our neighborhood, with devastating results. While we did not suffer much damage compared to many others, we were without power for fourteen days (a record for us) and a tree struck the front of our house, doing serious damage. Among other things, my antenna system was completely erased.

Sandy 10/29/2012

Sandy 10/29/2012

It wasn’t a big commercial antenna or tower or anything like that. I have always used simple wire antennas, supported in various ways. At the time of the storm, I had a mast attached to the second story of our house, supporting the apex of a doublet hung in a sloper configuration, and fed with 450 ohm window line. Pretty effective, and very cheap.

The mast was composed of those four foot fiberglass mast sections you can find on eBay. I think I had six or seven sections of the stuff hooked together, which starting from the second story of the house gave me about 35 – 40 feet at the apex. The mast was attached with brackets to the clapboard side wall of a dormer extension.

These mast pieces were never intended to be used to construct a tall mast. My understanding is that their intended purpose is to be used, one or two pieces together, to support camoflage netting. You know, when they hide airplanes under a lot of fake foliage. And I can attest to the fact that they don’t work very well for tall masts. I once tried to make a 40 foot mast out of the stuff, and attempting to get it vertical was a complete failure – rather like trying to stand a stack of cooked ziti on end. Al dente, of course.

Anyway, in the aftermath of Sandy I had nothing left but a pile of mast pieces and some tangled wire. In the days that followed, I scavenged the still usable bits, and put up a shorter version of the same arrangement, minus one piece I think. This second incarnation was liberally reinforced with Gorilla tape, and was splinted with four pieces bamboo around one particularly dodgy joint. (We had a lot of cut bamboo on the property, but that is another story for some other time.) The slightly crooked, splinted, shorter mast proudly adorned our house for about two years. You can guess that we don’t live with an HOA. My wife. God bless her, is very tolerant and allowed me to continue to persue my radio interests with this abomination attached to the house, but I must admit that even I would occasionally look up and mutter “got to do something about that antenna…” Oddly enough, when I looked for some pictures of the splinted version I couldn’t find any. I guess we didn’t think it was that photogenic.

In any event, last winter, which was very severe, finaly brought the matter to a head. After a particularly bad storm later in the season, the top of the thing snapped off. Ironically, it was the join above the bamboo splints that failed. I took it down again removed another section, and refreshed the duct tape. It was abundantly clear at that point something had to be done.

Sad remains of old mast

Sad remains of old mast

Over the summer, I started shopping for a new mast. No point in waiting, get it done while the weather is good. I dithered about comparing lots of different masts on the internet. It didn’t need to be very tall, since it would be attached to the house, but I wanted something very sturdy; a telescoping mast would be fine, but it couldn’t be one of those lightweight portable jobs. No kite poles for me, it had to have some gravitas.

I finally settled on an MFJ-1904HD mast, which is apparently designed to hold five element 80 meter monobanders and the like. I found a pretty good deal on the mast, (including free shipping, which surprised me. I was afraid of the shipping on somehing like this.)

The mast arrived surprising quickly. Next step: wire. I have always bought my wire from The Wireman, and I highly recommend them. I decided to replace what I had up with all new materials, so I bought sufficient wire and window line to redo the whole thing. After I placed the order, I realized I hadn’t ordered quite enough wire, and called them. They adjusted the order without any fuss. Is is a delightful business to deal with.

With wire and mast on board, I waited for a weekend when we would be home based to do the work. On the first such weekend, I climbed to the sunroom roof, only to discover that the brackets on the existing mast were woefully too small for my new, robust mast. Back to the internet, to find bigger brackets. This proved tough – in the end I found only one bracket, made by Rohn, which could handle the diameter of my new, robust mast. I ordered them. They were backordered. We were out of town for a few weekends.

Finally, today, the new antenna went up.

The weather was glorious, a perfect October day. And my younger son was available to help with the roof work, a major plus.

Installation crew hard at work

Installation crew hard at work

I tried to plan out all the steps of the job: things had to be done in the correct order since I intended to use the mounting hardware and antenna center insulator from the old doublet in the new antenna. Here was the breakdown:

  • lower the ends of the old antenna
  • remove the center of the old antenna from the old mast
  • take down the old mast. This was the most nerve wracking part.
  • remove the old brackets
  • caulk the mounting holes
  • assemble the new antenna, which included
  • measure two halves of the wire doublet
  • assemble the center insulator with wire and window line
  • drill the new mast for mounting the new antenna
  • measure and install the new brackets
  • install the new mast, collapsed
  • mount the antenna on the new mast
  • extend the new mast
  • attach the ends of the new antenna to the support ropes at either end
  • raise the new antenna

As simple as that.

Carfully organized tools and materials

Carfully organized tools and materials

Remarkably, all this went totally smoothly. Nobody got so much as a splinter – I cannot express my gratitude sufficiently. And for some reason, this project did not require the usual three trips to the hardware store.

The new wire antenna is a 135 foot doublet, fed by window line. While not exactly resonant on any ham band, it loads easily on all the bands with a tuner. It is a popular configuration, if you Google it you will find dozens of write ups on it.

I measured my wire (two 67 foot lengths) by putting two tent stakes into the ground 11 feet appart, and making six turns around the stakes, plus a foot or so. Then I wrapped the wire around rectangles of corrugated cardboard to keep it out of trouble until deployed.

Hard to see wire staked out for measurement

Hard to see wire staked out for measurement

The center insulator is a device called a Ladder-Loc, which is designed to support the window line and reduce stress on the the wire-to-feedline connections. The one I have has been in use for over four years – it is a little faded from exposure, but in fine shape and back in service.

When I reconnected the wire ends to the support ropes and pulled them up, I realized something interesting – the old antenna had been much shorter than 135 feet. I thought what I had was a 135 foot doublet, but it turned out to be about 90 feet. I dimly remember doing a lot of calculations to come up with a good doublet length because I thought 135 would not fit in my lot. Apparently I was wrong, and am absent minded, but to good effect.

The new mast

The new mast

I didn’t make the final connections back to the shack until the sun had set. The new antenna loads easily on all bands, and despite the prediction of a geomagnetic storm this evening, 80 and 40 meters sounded lively. I’m totally thrilled that this job is done, and not a flake of snow has fallen yet this season. I’m looking forward to a winter of sitting snug in my shack, playing radio with a beautiful piece of wire up in the air.
73,
de N2HTT

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J-38 Madness

As I mentioned last post, the SKCC Weekend Sprintathon for October was all about keys. I heard all kinds of keys on the air during that contest, and many of them were J-38 keys. The J-38 is the quintessential, all American made, military surplus key that every ham cut his/her teeth on in his/her first station. They were cheap, plenitful, worked pretty well, and looked kinda cool with all that mysterious extra unnecessary hardware on the plastic baseplate. Everyone had one. Except me.

I was certainly aware of these keys out there, but not having been a ham in the golden age of WW II surplus (I’m the right age to have been a teenaged ham in the 1960’s, but didn’t get a license until much, much later) I didn’t come across any for a dollar at the army surplus store or anything like that. I think my first key came from MFJ, and was actually a paddle.

Even before that WES weekend, I would occasionally look for a cheap J-38 on eBay from time to time, but gone are the days when these things could be bought for a couple of bucks – I have seen them command totally out of line prices of eBay, and this fact has for the most part kept me safe. But on that fateful Saturday night of the WES, sitting up in bed with a tablet perusing my favorite eBay searches, I came across a new listing that would have serious consequences.

The listing was for a “new in box, sealed in wax, J-38 key”. New in box keys are not that unusual, you see lots of them on eBay, but they go for really high prices. Covered in wax was very unusual though. Also, the listings (there were two) had a really attractive Buy It Now price for a new key. I bit. It was a little impulsive, since the contents of the sealed box was not visible, but hey. J-38 was on the way.

Sealed in wax for freshness

Sealed in wax for freshness

The auction did have photos of another key which the seller said was the same as the sealed units. This other key was definitely not new, and was the “all white metal” variety of the J-38. I know this because I immediately started researching J-38 keys, and found a wonderful resource if you are interested in the history of these keys. Take a look at Scott Hill, N6IX’s excellent page on J-38 keys. A link from his main page promises “more than you ever wanted to know about J-38 keys“, and I found it fascinating reading.

One interesting fact was that the J-38 was manufactured by many different companies, to the same specifications under government contract. I guess this was done to avoid single-source problems during the war years. It means that there are several common varieties of J-38, all slightly different — different manufactures used different materials, and finished the keys in different ways.

A few days later my sealed box arrived. I set up to photograph it as I opened it, rather like an archeolgical dig. I had no idea what the package would reveal. The cardboard key box was wrapped in cloth tape, and covered in a thick layer of sticky wax. Thoughts of every B-movie featuring Egyptian tombs flashed through my mind. Dimly seen through the wax cover was a label that promised a J-38 key, a good sign

Wax covered label

Wax covered label

I tried to gently tease the package open, but the cloth tape was not yielding to gentle. Unfortunately, the tape was applied across the box end, obscuring a lot of the label, but if you look closely at the bottom you can see the manufacturer given as American Radio Hardware.

American Radio Hardware, seen dimly through the wax

American Radio Hardware, seen dimly through the wax

ARH keys are a common variety of J-38, found almost as often as the Lionel J-38. Yes, Lionel, the toy train company, made a boatload of J-38s during WW II. We will revisit this fact in a bit.

Anyway I was excited – I had seen pictures of the ARH keys and I like them a bit better than the more common Lionel variety. I continued to saw away at the box, a little less gently now. Finally, an end came open, and I found the key wrapped in what I would describe as butcher paper. There appeared to be oil or grease on the key, and staining the paper. Here is what it looked like unwrapped:

Finally out of the box

Finally out of the box

It didn’t look new to me, but in very good condition. There were some markings on the lever, and the gap adjustment screw was bent. Overall though, it was a pretty nice key.

It is of the variety that Scott K6IX describes as an all white metal key, containing no brass parts. The conformation is that of the ARH key, but the typical ARH key has brass parts as well as “white” metal. The interesting thing is that if it was new, the box would be evidence that ARH made at least some of the all white metal keys. However, I don’t think it was new. Perhaps whoever packed the key so carefully and sealed it in wax, maybe to bring it home as a souvenir after overseas service, grabbed a key and any box handy and paired them up. Who knows?

I sent an email to the eBay seller, asking for any information they might have about origins of the key. To my surprise, I got a reply almost immediately. The seller’s father had been in the Navy and had a number of WW II items, but beyond that nothing else was known. So whether the key is a white metal key made by ARH remains indeterminate.

I cleaned the key up using good old Brasso, and stuck 4 low profile feet on the plastic base. The base was warped slightly, (this is common with these keys) and wobbled a bit; the rubber feet cured the problem. The key has a very nice feel, and looks good, even with the bent adjustment screw. It’s a keeper

The white metal J-38 key

The white metal J-38 key

Ah, but now the fit was on me. Scott’s web page contained sage advice about how to clean up these old keys, and I decided to try for a Lionel key on the cheap. I watched for the most disgustingly dirty, but complete Lionel key I could find on eBay and bid on it, planning to transform it into a beauty with a little elbow grease. Before long, a Lionel key was on the way…

Lionel J-38 as received

Lionel J-38 as received

The key arrived in good shape, but pretty gritty.

Gritty close-up

Gritty close-up

Following Scott’s advice, and having a Saturday afternoon with nothing much else planned, I got started with my key cleaning event Friday night. Here are the steps:

  • Soak all the parts in household ammonia solution overnight. I collected the parts in groups, so I could figure out how they went back together. Also, I separated the white metal parts from the brass ones, not wanting any weird galvanic thing happening to them while soaking. I had visions of all the brass bits disappearing overnight or something like that. I have a bunch of these all-plastic ice cream jars (the family consumes a bunch of this stuff, good ice cream, great jars) that were ideal for the task. As Scott predicted, the white metal parts turned black overnight, but this is expected and not harmful.
  • Initial polish with Brasso. This removed the residue from the soaking.
  • Polish the parts again with Flitz Blue. You can find it on Amazon. This stuff is amazing. You can even use it on the painted parts, diluted.

Speaking of parts, there are many more that you would think for a simple looking key. The left side parts:

Left side bits

Left side bits

The center parts

The center bits

The center bits

The right side parts

The right side bits

The right side bits

The white metal parts

The white metal bits

The white metal bits

And the weird connective tissue parts. These are mostly insulating washers, critical to the functioning of the key.

Tiny weird bits

Tiny weird bits

Those little wire bits that look like broken ends from mechanical pencil leads are parts too. The are pins that orient the terminal posts so that the holes line up with the markings on the base. No kidding. Only the Lionel keys have them. It was a miracle that I didn’t lose any, and they made re-assembling the key an exquisite experience.

All put together, the Lionel key looked great cleaned up:

Lionel J-38 reassembled, no base

Lionel J-38 reassembled, no base

but it suffered from a pretty bad warping of the base plate and was quite wobbly. While it meant forgoing the extraneous hardware bits, I mounted the key on a block of pretty hardwood (also an eBay purchase), mounted low profile rubber feet, and am rewarded with a very nice looking final product:

Lionel J-38 - final product

Lionel J-38 – final product

Those extraneous bits? These keys were used to train new operators, by wiring the keys in series with the instructor’s key and oscillator. Headphones were wired in series with the keys, and the shorting bar allowed the trainee to listen on the headphones while not sending. The eyelet was used with a cord to tether the headphones to the key, so they wouldn’t wander off at the end of the training session.

Having refurbished two of these keys, I will definitely enjoy using them. They feel good and impart a sense of history, especially hooked up to boat anchor rig. My obsession with J-38s is starting to wane – the doctor says that in two or three weeks it will all pass, and I can have access to my eBay account back again.

73,
de N2HTT

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If it ain’t fixed, don’t break it.

This past weekend saw one of my favorite operating events, the Straight Key Century Club (SKCC) Weekend Sprintathon. Just a bunch of guys sending slow to medium speed CW, exchanging SKCC numbers, and generally hanging out amidst an atmosphere of general ham radio bonhomie. I much prefer it to the monthly sprints, which are also fun but only last two hours in the middle of the week. The two hour thing generates mild anxiety on my part, I feel performance pressure. No, the WES, which lasts 24 hours, is really relaxed and totally pleasant.

Each month’s Sprintathon has a theme, usually topical in nature. The theme is used to structure bonus points in the competition and usually involves some addition to the contest exchange. The theme for the October Sprintathon was “OctoberFest” – I’ll explain in further detail what that has to do with this post in a bit.

I was excited to realize that this month’s WES would coincide with my being a the upstate QTH, where I have been setting up a vintage, tube based station. What better way to shake out those tubes than to participate in a low key (no pun intended) CW contest? Since my last post (The QRP Blowtorch) on the upstate QTH, some things have changed…

Over the summer, in the midst of my preocupation with the Drake 2-B, I spent a lot of time looking at boat anchors on eBay. I think what got me started was seeing an auction for an Eico 723, which looked really good. Didn’t win it though.

I kinda got fixated on the idea of one of these small “novice” transmitters. They are not huge in size, mostly crystal controlled, and typically put out about 40 watts for the novice maximum input power of 75 watts. After much looking around, I found an auction for a nicely refurbished Knight T-60. This rig is typical of the breed; the one I found had already been re-capped and was described as working. It had a minor blemish on the cabinet, which is probably why I got it for as little as I did. When I tested it, it was in fine working order, and the blemish did not seem to have any impact on its transmitting abilities. It pulls about 60 watts input, and can put out more than 30 watts when tuned for “maximum smoke”.

Knight T-60 Transmitter

Knight T-60 Transmitter

I brought the T-60 to the upstate QTH, and carefully installed it at the operating position occupied by the QRP Blowtorch. The Blowtorch is now occupying a place of honor in our living room bookshelves, ready to spring back into action in a moment’s notice.

On the shelf, ready...

On the shelf, ready…

But the lure of those 30+ watts, given the limitations of being rockbound and the general lousiness of band conditions of late, was irresistable. I am a QRP guy through and through, but occasionally one needs 30 watts. It’s good for the soul.

The T-60 uses cathod keying. Typically cathode keying runs about 100 vdc on the key, and you need to be very careful where you put your fingers. For that reason, I have certain keys that I prefer to use with the tube rigs. One of which is my Soviet Military Key (SMK). These keys can still be easily found on eBay – they date from the 1970’s and were surplussed out in large numbers. From what I have seen on eBay these days, they are a bit more expensive than when I bought mine about ten years ago. They are still a great value though: easily adjustable, pretty good feel, and best of all totally isolated from the keying circuit. The key arm and contacts are protected by a plastic shroud, and the exposed portion of the key arm is completely made of (or covered in, I’m not sure) heavy plastic. Unless you deliberately place your fingers across the screw terminals at the back of the key, there is no way to get into any trouble. Safety first, I say.

Soviet Military Key

Soviet Military Key

Soviet Military Key with the hood open

Soviet Military Key with the hood open

So imagine my surprise when I hooked up my Soviet Military key to the T-60, and it wouldn’t key! One of the nice features of the T-60 is that is makes use of modified cathode keying, that only puts a few volts across the key. It turns out that the Soviet Military key, with the key closed, presents a resistive load of about 40 ohms across the contacts. Apparently that was just too much for the tubes to key. Closing the key was going from “very open” to “still pretty open” and it just wasn’t cutting it. So for WES this month, I used a different key (who doesn’t have a selection handy?) and proceeded to operate very successfully with the T-60. (I also did a bunch of QRP contacts with the KX3. Couldn’t help it.)

After WES ended, I decided to have a look at the innards of the SMK to see where that 40 ohms is coming from. I was vaguely aware that there was some kind of filtering or key shaping circuitry inside the key, obviously designed for use with high voltage rigs. (The SMK has worked very well with the W1TS Simple Transmitter, and an HW-16, the 40 ohms not causing any issues with these rigs.)

Removing the base plate exposes the filter board, with a collection of caps, large inductors, and a couple of 20 ohm resistors. Hmm…

SMK filter circuit board

SMK filter circuit board

Lifting the filter board revealed four wires, from the four contacts topside to filter board. It was a fairly simple matter to unsolder the board from the terminals, the wires from the board, and solder the contacts directly to the terminals.

Filter board removed, contacts wired directly to terminals.

Filter board removed, contacts wired directly to terminals.

In looking at the connections, I discovered an interesting fact: The metallic arm of the key is completely electrically isolated from the keying circuits. It is connected to the ground terminal, but the keying circuits float isolated from this terminal. This is a really safe key.

SMK contact details

SMK contact details

The three terminals on the rear of the key, marked “a”, “b”, and “c” make up the keying connections. The way I wired mine, “a” — “c” are the keying terminals. “a” — “b” are normally closed, and open when the key is pressed. This could be used for muting your receiver, kind of manual QSK.

After everything was buttoned up, the key works beautifully with the T-60. The station looks very nice all put together.

The whole 30 watt enchilada

The whole 30 watt enchilada

The OctoberFest theme? Every exchange had to contain the manufacturer of the key you were using, and you get bonus points for each unique key manufactured you worked in the contest. I used my Palm Radio PPK key for WES. I heard (but did not work) at least one “SOVIETMILITARYKEY” in an exchange, so there is at least one other out there.
WES is over for this month, but I’m looking forward to making some more contacts with my rock crushing 30 watts, and a very safe key.
73
de N2HTT

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2B Redux

My infatuation with boat anchors has begun to reassert itself this summer, with the sudden acquisition of a Drake-2B receiver. I like working with separates: a tube transmitter like the W1TS Simple Transmitter or the QRP Blowtorch, and a vintage receiver as a companion. The Drake 2B has an excellent reputation, it is readily available, and most importantly, it is relatively compact for a tube rig.

During the month of August I started looking at the classified ads for a 2B, and of course, found several excellent deals which I had just missed. Now I know lots of folks find great buys at local ham fests, but for some reason the timing is always off for me. I manage to get to maybe two ham fests a year, and never in midst of summer. eBay is my constant, 24/7, exorbitantly priced personal ham fest. Rather than being patient, my immediate gratification gene kicked in, and I turned to eBay.

I found a 2B auction for a nice looking unit, not too expensive, whose owner described as “working”. After many years of buying used equipment on eBay, I have figured out the meaning of “working” with respect to eBay:

working, adj.
1. Not totally moribund; will light up if plugged in.
2. We don’t know how to test it, but didn’t find anything wrong.
3. It was working perfectly when we put it away 18 years ago.

This auction was accompanied by many encouraging photos of the rig all lit up, and the assurance that it was in good condition. There certainly wasn’t any doubt that the panel lights worked.

Drake 2B, working.

Drake 2B, working.

When the rig arrived, it did look good, and lit up most emphatically. My initial assessment of the received audio though was only so-so:

  • there was a ferocious AC hum on the audio
  • the audio levels were very low – full AF gain was barely driving an 8 ohm speaker
  • the diode detector didn’t seem to work – I couldn’t find any AM signals.

I had pretty much expected that I would have to replace the electrolytic caps – this would most likely fix the hum. I ordered a re-cap kit from Hayseed Hamfest. These folks make up multiple caps in pin-compatible metal cans that will exactly replace the originals. The kit for the 2B consists of a replacement can containing four caps, and a single, stand-alone electrolytic. They also thoughtfully include a length of solder wicking braid for use unsoldering the old components.

While I waited for my re-cap kit to come, I started hunting down replacement tubes for the 2B on eBay. In general I like to have spare tubes on hand for any of the boat anchors in active use, and I suspected that a few tubes might need changing in my ailing 2B. The 2B uses ten tubes, seven different varieties; happily all of these tubes are easy to find and not too expensive. With judicious bidding, over the course of several weeks, I was able to come up with at least two replacements for each tube in the rig, at an average price of about $2 a tube.

Perhaps an obsesssive quantity of spare tubes.

Perhaps an obsesssive quantity of spare tubes.

The end of summer, and beginning of the school year are hectic times in our family, so it wasn’t until the end of September that I found a weekend with sufficient time to tackle the rig. Coincidentally, W2AEW, Alan, had just produced a series of four excellent YouTube videos documenting his refurbishment of a Drake 2B. Alan’s instructional videos on electronics and ham radio topics are superb, I highly recommend them.

After printing off a copy of the 2B manual I found online, I put the rig the bench and opened it up. No obvious damage was apparent, a good sign. Using the resistance chart in the manual, I checked the resistances to ground from each pin of each tube. This is a useful exercise, because it takes you on a tour of the major functional blocks in the radio. For the most part, the resistances were in the ballpark, so I pushed on.

2B resistance checks.

2B resistance checks.

Examining the underside of the chassis in the area of the canned caps revealed a surprise. It seemed like there were some components in the rig that did not belong there! Oh no, a mod! Just to be sure, I reviewed Alan’s video where he showed the same area of his radio – stopping the motion to freeze the frame on the screen. No doubt about it – there was an alien invasion in my rig.

Alien invasion!

Alien invasion!

Identifying the connecting parts, I was able to localize where these caps had been added on the schematic to try to guess their function. First, I searched the web to locate common mods for the 2B, to see if any of these matched what I had found. No luck. There are a few widely reported 2B mods, these were not they. The best I could guess their function was:

  • the cap in series with one pin of can might have been an attempt tame the hum?
Extra 150uF cap attached to can.

Extra 150uF cap attached to can.

  • the other two caps were both at points between the detectors and the audio preamp, going to ground. More hum suppression? Maybe trying to shape the audio?
Two other 25 uF caps at points between detectors and audio stage.

Two other 25 uF caps at points between detectors and audio stage.

If anyone has any thoughts about why these might have been added  I’d love to hear from you.

Anyway, I took a deep breath, and ripped them out. Now everything looked as expected. Before making any changes, I took a number of detailed closeup photos of the area where the work was to be done. This is invaluable for getting all the wires and components that connect to the caps back where they belong.

Base of the can caps, before replacement

Base of the can caps, before replacement

The other electrolytic to be replaced.

The other electrolytic to be replaced.

The re-capping itself went fairly smoothly. I use a Hakko 808 desoldering tool (I highly recommend this tool, especially if you do a lot of repair work, or just make a lot of mistakes) which worked splendidly to unsolder all the lugs. However, the two of the tabs that hold the cap-can to the chassis were soldered most enthusiastically, and the 808, which has a rather delicate tip, was struggling to melt the solder blobs.

The Behemoth

The Behemoth

I used a 250 watt iron in one hand, and the 808 in the other to melt and vacuum up the solder. Even at that I had a bit of a struggle prying those tabs off the chassis. Eventually the can worked free. The new caps went in without a hitch, and I was left with a very nice piece of leftover solder wicking braid as a backup.

Once the recapping was done, it was time to pay attention to the tubes.

I have a very nice tube checker, a Hickok 6000A, which I got at the annual PCARA Bring & Buy Auction two years ago. It’s in good shape, and every once in a while I pull it out and check a tube, just for the heck of it. It’s also good for checking all those NIB/NOS* tubes from eBay. *[New in Box/New Old Stock]

I didn’t want to change out all of the tubes in the 2B blindly – instead I wanted to check each tube in turn, and only replace one if it seemed the replacement would improve matters. I tested each tube in turn, using the following rules:

  • check for shorts. Shorted? out it goes.
  • check for leakage. Excessive leakage – discard.
  • emissions check. Here some judgement came into play: If the tube tested good on the test, keep it. If not, apply the same test to one or two of the replacement tubes, and only swap the tubes if the replacement fared better in the test.

The reasoning behind this last rule is simple: I have never tested the tube checker with known good tubes, or had it calibrated or refurbished. For that reason, a “low” emission reading for a particular tube is just a likely an indication of a problem with the tester as it is with the tube. The emission test values are kind of a qualitative measure, not like a short, which is a pretty deterministic game-ender.

Anyway, using this protocol I found four tubes I felt needed replacing.

The rogues gallery.

The rogues gallery.

  • the 6X4 showed several shorts. The replacement tube did not.
  • the 6U8 had next to no emission reading. The replacement read “good”.
  • two of the 6BE6 tubes had low emission readings, but the replacements read “good”.

There were a few of the other tubes that had low emission readings, but were consistent with readings from a sampling of replacements. I didn’t replace these. Most notable among this group was the 8BN8. This tube runs at a higher filament voltage, 7.5v, and I wonder if my tube checker is having problems maintaining the higher filament voltage.

With tubes updated, and re-capped, the rig sounds great. The audio is way up from before, in fact about 20% of the AF gain setting is a comfortable listening level with the same speaker. The diode detector now works – I can now find AM on 80 meters no problem. (Lots has been written about listening to AM on the 2B being somewhat sub-optimal, because the widest filter, 3.6 kHz, is rather narrow for AM. I don’t think I will be using the rig a lot for AM, but it’s nice to know it’s working.)

And the 40 meter CW subband is alive again! Lots of signals, and pretty good selectivity with the 500 Hz filter. It now sounds like a radio.

Photo of beautiful CW audio coming out of the refurbished 2B.

Photo of beautiful CW audio coming out of the refurbished 2B.

There is probably more work to be done on the 2B. I’m sure it could benefit from an alignment, and I’m looking into how best to accomplish that. The alignment procedures are simple, you just need an RF signal generator. I have a old analog tube model; I need to see if I can control its output levels well enough to use it for the task. That may be the subject of a future post.

I also have the matching speaker and Q-multiplier for the radio. The speaker works FB, the Q multiplier doesn’t do much of anything, but you can get it go into oscillation if you overdrive it. This piece of gear will probably be the subject of some future poking.

The weather is getting colder and wetter, making bench time look ever more attractive. There are lots of projects waiting in the wings, I’m looking forward to lots of chilly evenings spent snug in my workroom, tinkering.

73,
de N2HTT

 

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The QRP Blowtorch Rides Again

Summer in the Northeast is the perfect embodiment of the 80 / 20 rule: we get 80 percent of our outdoor activities in during the 20 percent of the year when the weather is nice. We really are having a lovely summer so far in New York, and as a consequence I am not spending a lot of time at the bench, or writing blog posts for that matter.

The emphasis has shifted to operating for me this summer, preferably out doors, portable QRP. My first efforts along these lines was a shot at sea side QRP CW from Cape May New Jersey early in July. Using a 20 foot crappie pole as a support, I put up a 20 meter end fed half wave antenna in a sloper configuration, and launched a mighty signal (about 2 watts) skyward using my FT-817 and a slew of NiMH batteries. I got curious inquiries, and actually some encouragement from passers by on the beach, but my signal was so puny I wasn’t even picked up on RBN. Also, there was S9+40 noise from some source near the beach, so I probably wouldn’t have heard a reply if there had been any.

QRP on the beach

QRP on the beach

And yet, it was really enjoyable to try. I view portable QRP efforts like fishing: sometimes you get a nibble, sometimes not, but the trip is always worth it.

The main story that has been unfolding this summer is that of setting up a new QRP station. It is something of an involved tale, so let’s go to the beginning and follow it along.

Back in April of last year, I was selling my HW-16 station via the PCARA club table at the OCARC hamfest. It was a complete station, including a VFO and a matching Heathkit speaker. A photo of the event appeared in our club newsletter, and my fellow club member and good friend Karl Zuk N2KZ had noticed the HW-16, and specifically the speaker, in the photo.

PCARA Table at 2014 OCARC Hamfest

The photo that started it all (by Malcolm Pritchard, courtesy of PCARA Update)

This April Karl sent me an email, asking whether I still had the speaker. As it turns out, by the time Karl has asked, the station was gone, but I had another similar speaker that was paired with an HR-1680 Heathkit receiver. Since I was intending to part with the HR-1680 anyway (the Heathkit gear is cool, but mostly too large for the spaces I have available) I offered the speaker to Karl gratis.

Karl countered with another offer: he had a homebrew, tube QRP transmitter that had been given to him, and would I be interested in a trade? Absolutely! Tubes, homebrew, QRP, potentially dangerous voltages, what’s not to like? So we agreed to a swap. Karl and I exchanged a few emails trying to set up a date to meet, but it wasn’t until the middle of May that we were able to post up.

Shortly after of Karl’s first email, I decided to re-arrange my QRP stack to use the HR-1680 receiver (but not the speaker) instead of the FT-817 with my tube transmitter. I was not having any success selling the HR-1680 anyway, might as well use it as part of the station. It just fit in one of the cubbies of my operating desk — and that was better than letting it take up space on the floor. Hooked up to the Magic Box (t-r switch), it played nicely with the 2-tube transmitter.

HR-1680 in the QRP stack

HR-1680 in the QRP stack

The month of April and part of May sped by, and finally Karl drove by my place one Saturday and dropped off a bankers box containing the rig and some documentation from the original builder. It was bigger than I expected, and two pieces: a 250v power supply, and the actual transmitter itself. It was impressive – not the least because it sported a prominent label, in large red letters, reading “DANGER HIGH VOLTAGE” right in front. This was a serious rig.

The QRP Blowtorch

The QRP Blowtorch

The rig had a name: The QRP Blowtorch. The documentation, written by the builder of the rig, Stan WB2LQF, was detailed, including copies of the original articles that inspired the rig, and a journal entry from Stan with his thoughts about it, including observations about what needed improvement.

The rig is an implementation of design from an article in the January 2003 QST, entitled “The Two Tube Tuna Tin Transmitter (T5)” by Steve Johnston WD8DAS.

It was a classic MOPA design, using the same two tubes as my 2-tuber: a 6C4 oscillator, and a 5763 final amplifier. In fact, the guts of the two circuits are almost identical. It came with a clever power supply made from two filament transformers back-to-back, using a diode voltage doubler to produce a B+ voltage of 250v. The article claimed an output of 5 – 8 watts. I’d be thrilled with five.

I figured I might do some checkout on it, and maybe the two mods Stan mentioned in his notes, and then take the rig up. Putting it on the bench for checkout revealed a very competent point to point wiring job, and no surprises. Everything looked ship shape, I would have no qualms about firing it up.

Stan had mentioned in his notes that he intended to add some more filter capacitance to the power supply, and possibly to the output tank as well. I ordered a couple of caps from Mouser and added them to the PS, but I wound up not do in anything to the tank. It seemed to be to be loading up just fine on 40 meters, so I let it be for now.

Additional filter caps strapped on

Additional filter caps strapped on

My immediate impression was that the rig was too big to try to incorporate into the QRP stack, with the two bulky boxes and interconnecting cables. We are fortunate enough to have a vacation home in central New York state, where presently I have no station set up. The QRPBT seemed a likely candidate to become a permanent second station at the up-state QTH.

Upstate QTH - Flamingo garden

Upstate QTH – Flamingo garden

To set up a permanent station, I would need three additional items:

  • a receiver,
  • some kind of T-R switch,
  • and an antenna tuner.

The T-R switch was easy: MFJ makes a simple unit with RF-sensing, the MFJ-1708, that got good reviews on eHam. Looked like just the thing, and I ordered one forthwith.

MFJ-1708 T-R Switch

MFJ-1708 T-R Switch

The receiver was another matter. Having just committed the HR-1680 to use on the QRP stack, I needed to figure out something else. I was fresh out of receivers. So taking this as a cue to go shopping, I started to look around on the classified ads and eBay, deciding that a vintage tube receiver would be just the ticket. There are lots of boat anchor receivers out there to be had, but the one that kept floating to the the top of the searches was the Drake 2B. (Or 2A, I’m not picky.)

This receiver seemed to offer many plusses:

  • It is relatively compact for a tube rig.
    (The typical Hallicrafters receiver takes up a standard parking space, including the matching speaker.)
  • They are very highly regarded, positive reviews abound.
  • They are plentiful. If you can’t find one on eBay, wait 5 minutes.

I started looking.

I didn’t have to look long. Several classified ads and eBay auctions later, I found my new (old) receiver. In nice cosmetic condition, and good operating order, a working Drake 2B arrived soon. What a lovely receiver. I set it up, hooked up antenna and plugged it in, and began to explore 40 meter CW with it. I was sold.

My 2B was made around the mid-sixties, about the same time as the original QST article that described my 2 tube transmitter came out. They are a good pair, and I decided to keep the 2B in the QRP stack, and move the HR-1680 upstate. I expected to have to do major surgery to the operating desk, but it turned out that simply popping out one shelf did it.

Drake 2B in the QRP stack

Drake 2B in the QRP stack

Okay, so transmitter, check; receiver, check; t-r switch, check; the only remaining item was an antenna tuner I could leave upstate. Back to the ads.

This time, I found the field on eBay to be a tad expensive for my tastes, but a nice MFJ-941c turned up in the classifieds for cheap and I jumped on it. The 941c is not without its faults, but it serves perfectly in the new station.

The QRP Blowtorch in its new home

The QRP Blowtorch in its new home

So finally, in mid-July, the QRP Blowtorch made its debut. On Sunday 7/26, after hanging around on 7.054 for a while, I called WO1W, Gene in Rhode Island, and we had a brief but solid QSO lasting about 10 minutes. Gene gave me a 589, which pleased me greatly, and the QRP Blowtorch had indeed ridden again.

There are several weeks left to the summer, and I am looking forward to making a several more QSOs as the warm breezes waft in through the shack window, illuminated by the glow of those tubes.

The glow.

The glow.

73, de
N2HTT

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