A Covert and Patriotic Not an Antenna Idea

 

Wow, it's hard to believe that it's been over two years since my last post.  Normally, that would be indicative that I'd lost interest in doing so, but the real reason is simply that I haven't done much in the way of radio projects because of a couple of major, unrelated projects that I've been working on for the past couple of years.

One project involves a mobile home in a senior citizens complex in Central Florida, but we won't get into that, this being a radio and not a mobile home improvement blog, other than to say that the complex prohibits antennas but allows flagpoles.  I knew that was something I could work with, I just didn't know how, but the idea had been planted.

Before continuing, there is a vendor who markets a ready-to-go, turnkey flagpole antenna for under a grand.  Unless you like the adventure of rolling your own, that's probably a better way to go.  For the rest of you sickies:

While this project was festering in the mucky recesses of my mind, I picked up one of those Chinese N7DDC ATU-100 autotuners from Amazon, and was pleasantly surprised by how well it worked; it operated quite quickly and reliably matched almost anything I threw at it, so I wondered how it might do as a remote tuner for a flagpole vertical.  The answer: Quite well.

Remote ATU-100 tuner in weatherproof box.

Having convinced myself that the idea might just work, I ordered a 25' telescoping flagpole (About $80 from Amazon.)  The base section of the flagpole slips into a thin plastic sleeve, which I discovered fits reasonably well into 2 1/2" PVC. So, I cut a 3' section of this, glued a 19" section of 2" PVC inside of it so that, when planted in the ground, the base of the flagpole rests just above ground level, on top of the 2" PVC section.  A hole is drilled near the base for the connection from the tuner, and just below that hole is the connection point for the ground radials. A short length of ladder line connects the antenna to the remote tuner.

PVC Base and tuner.

From the remote tuner to the shack are two cables: One coaxial feedline and one power/control cable. On the bottom of the remote tuner, an SO-239 connects the feedline and a common 8 Pin mic socket the control cable, for which I used direct-bury lawn irrigation cable.

Tuner controls mounted in Astron Supply.

Being somewhat space-limited in the shack, I mounted the power and control switches/wiring in my Astron supply.  Another 8 pin mic connector is installed on the rear of the supply for the control cable.

Operationally, the antenna/tuner will find a "match" on all the HF bands, automatically, within about a second of detecting a carrier or more than a handful of watts. Obviously, as a short, vertical radiator, radials are essential and mine are less than optimal, so my performance on the lower frequency bands (160, 80, 60) isn't as good as it could be, but it works.  On 40, things get better, and on 30 and higher, it works quite well.

Quite well, indeed, considering that it's not an antenna.

The Complete DXer

Odds are that, if you're reading this, you're probably familiar with two other jewels from the ARRL bookstore: Solid State Design For The Radio Amateur and Emperical Methods of RF Design.  An equally important (and still available!) publication is Bob Locher's The Complete DXer.  In a nutshell, TCD is to operating as SSDRA and EMRFD are to homebrewing - essential reading, and a bargain at $19.95.

So, what got me on this topic?  Well, dialing around during this pandemic, it's obvious that some of you could use a little elmering. Since we're not supposed to be around each other, I can't come over and teach you what was taught to me, but reading OM Bob's book can! Read it, learn it, live it and you'll come to love it.

If you can't, for whatever reason, read TCD, I'll let you in on a little secret:  There's an old adage that goes "Can't work 'em if you can't hear 'em".  Most assume that refers to using a decent antenna or well designed receiver, but there's a non-hardware component as well: You can't hear 'em while you're transmitting. 

Here's an exercise: Next time you hear a pile-up, listen to it critically.  Who's he working? Why? Is he following a pattern, eg: listening a bit up or down with every QSO? Is he giving instructions?  Once you develop that sort of awareness, then you'll know where to call and when to do it.  Practice that, and not as many of us old QRP guys will be cracking the pile before you get your turn, certainly before the lids calling "Who's the DX?" get theirs.


Enough of the lecture.  Go get the book and start working to become a better operator.

Social Isolation and the Icom 735

N8NM/p, Lakeland, Florida

I'm not to proud to admit that my homebrew rigs sometimes don't travel well, so when my wife and I were planning this extended trip to Florida, I thought it'd be fun to reacquaint myself with an old friend: Icom's IC-735.  So, I pulled it down from the shelf where it's sat for years, and stuffed it under the back seat for the 1300 mile ride, never giving thought to whether it'd work when we got here.  

That's trust, and I wasn't disappointed.  Other than the meter's backlight being dead, the old rig still works as well as it did when it came over from Japan during the Reagan Administration.  Better, actually, thanks to some nice International Radio crystal filters that I installed years ago.

I was a part-time tech in a local ham radio store, they still had such a thing in the mid-'80s when the '735 came out, and I remember thinking that, with all that's crammed into that box, I'm gonna hate working on them.  We sold tons of them, and almost none made it to the bench for anything other than having options installed.  At nearly $800, they were out of my reach until the next new thing came out and they started showing-up second-hand.  So, it was probably about 1990-1991 before I could get one of my own.  I sold that one a few years later, regretted it, and probably bought this one somewhere around 2000ish.  I know I had it shortly after 2001, because it was unfortunately damaged by a hasty repackaging job performed by a member of a new branch of government called the TSA.  Luckily, the damage was cosmetic - the bottom panel was caved in - and the electronics were unharmed.

In the mid 2000s, I added a second IC-735 to the fleet and equipped both with the aforementioned aftermarket filters and tweaked them so they'd go down below 5W (the minimum was 10 from the factory).  Using them as a portable SO2R contest station and with wire dipoles, I won the QRP class in quite a few state QSO parties, including in-state wins in Michigan and Tennessee.  I beat the poor things like rented mules, and only managed to break one once when I blew some switching diodes out on the bandpass filters by accidentally getting my cables mixed and transmitting directly into it.  

I suppose that makes the rig Idiot Resistant rather than Idiot Proof.  Fortunately, 1N4148s are pennies and the repair took maybe an hour, and I haven't done that again.

So, here I am, enjoying my first winter someplace where the air doesn't hurt, and along comes this pesky virus from far away.  It looks like I may be here a while, but that's OK - the weather's nice and, as someone who spends his time building ham radios in his basement, I'm well adapted to social isolation.

I've got my '735 and soldering iron set-up out in the lanai, the sun is out and the weather is warm.  I think I'm gonna be OK.

A Homebrew Stereo for the Shack

There are times when it's nice to listen to a little music while working at the bench.  For years, I've used a number of different vintage radios for this purpose, but few of them had the modern FM band and none were stereo.  So, I did what any other geek would do and built my own!

A battered old Eico HFT-90 that I had stashed in the attic over my garage provided the vortex that sucked me down this hole.  I don't remember how I came to own this thing, but I've been lugging it around for probably 30 years and it was finally time to do something with it.

It was in pretty rough shape, but it didn't offer up any real fight in my efforts to revive it; the only problem with the electronics were the filter caps were long shot and the controls were dirty.  Cosmetically, though, while the chassis was fine, the cabinet was rusty, so it was a total strip and respray.

But, you might wonder, isn't the HFT-90 monaural?  Yes, but that's easily rectified in any number of ways.  I would have liked to build a tube-based converter, but as a concession to practicality, went solid state using a discontinued device from 40 some years ago, the LM1310.  I was already familiar with that chip, my first job in electronics was working on consumer audio equipment and that chip was everywhere.

The MPX converter is the box above the tuner.  I built it from scrap sheet metal and sprayed it with left-over paint from the tuner.  The circuit is straight from the datasheet, works perfectly and only requires a handful of parts.  The large red lamp is the pilot detect light; the jeweled lens came from the junk pile and it's lit by a clear LED. 

As for the amplifier, I wanted to use tubes for some odd reason, and what better tube for something like this than the dirt-common 6AQ5?  And what better to drive it than a 12AX7?  And what better to use for a chassis than an inverted cake pan?  Honestly, I can't think of anything!

Again, the circuit is plucked straight from the datasheets.  It's the same one found in gazillions of TVs produced in the 50s into the 70s, and is perfectly adequate for this project.  No oxygen-free cables or gold plated binding posts here.  Actually, I did make one modification - I increased the cathode resistors to 1K because the power transformer from my junk-box is a little undersized.  Speaking of transformers, the outputs came from Antique Electronic Supply and I think they were made by Hammond.  They represent the only money spent for parts, about $35.

The speakers are also homebrew using 8" drivers from Parts Express.  The cabinets are built from 3/4" MDF and are sized based on the specs of the drivers at about .75 cubic feet.  I wrapped them in maple veneer because I've never seen maple speakers before.

So, how's it work?  For its intended purpose, filling a 12x14' room with sound, it works perfectly.  With maybe two watts per channel, it's not going to rattle the widows, but for kicking back sipping some Tullamore Dew while listening to Miles Davis, it's good enough.

Mic Amp/Limiter for uBitx

The past few months have been very busy for me, but I somehow managed to knock-out a Version 5 uBitx.  Pretty incredible little rig, congratulations, Farhan!

As it comes, the uBitx is set-up to use a condenser microphone, but it doesn't quite have enough gain to be used with my beloved Astatic 10D.  Not wanting to have yet another microphone on the desk, I adapted the mic amplifier circuit that I used in the SR-16 for the uBitx. 

The circuit is based around the common LM-324 quad op-amp and will work equally well with pin-compatible chips like the TL-074 or TL-084.  The circuit is installed between the dynamic mic and the input to the uBitx, where the mic bias voltage provides the VCC for the op-amp.  I installed it in the rig, though it could just as well be installed in the base of the microphone, provided space exists. 

The circuit itself is pretty straightforward: The first stage is a typical inverting amplifier with about 20 dB of gain.  This feeds the limiter stage, which clips any positive or negative signal peaks exceeding about .7V.  The limiter is also inverting, so the signal at its output is in-phase with the input signal from the microphone (not that this is important...) 

The limiter is followed by a low-pass filter to remove any high-frequency artifacts created in the limiter.  The "knee" of the filter is around 3KHz. This is followed by a buffer stage to provide a low-impedance output to drive the rig. Resistors R4 and R5 form the voltage divider used to provide virtual ground (1/2 VCC) for the first two stages. 

The output of the buffer probably looks odd, what with the two caps and all.  What I'm doing there is creating the equivalent of a 2.35uF non-polarized cap.  This is probably unnecessary; thinking about it,  C9 could be eliminated completely because the DC voltage at pin 14 will always be lower than the uBitx's mic bias voltage.  But, lets ignore that for now.  The DC bias voltage is routed, through R10 to capacitors C2 and C3, which remove any AC from the DC before applying it to the LM324.  Resistors R4 and R5 form the voltage divider used to provide virtual ground (1/2 VCC) for the amplifier/limiter stages, the filter and buffer are "self biased" to 1/2 VCC by the output of the limiter. 

I optimized the gain to suit my 10D/D104 mics, and as such, really have to eat the microphone before it sounds nasty.  This is born out by the reports of "excellent audio" from the 40m SDR police, so I'm satisified with its performance.  If, however, it doesn't provide an appropriate amount of gain for a different mic, that can be adjusted by changing the value of R3 as the gain is determined by the formula AV = R3/R2.  The reason I say to adjust R3 instead of R2 is because R2 pretty much determines the input impedance of the circuit, so you want to keep it around 500-1K.

Homebrew WAS

 

Could this be the first FT8 WAS earned using only QRPish (10 Watts) scratch-built homebrew gear?  If not, it's got to be a very small club.
I'm not much into paper chasing, but see the appeal of it and would love to see the ARRL (and other amateur radio organizations) recognize our accomplishments in the realm of homebrewing much the same as they do contest results and DXCC stats. 

After several years and moderate success as a DXer and contester, I was totally burned-out until I added the homebrew dimension.  How many more of us are out there?  Certainly, I can't be the only one.

ARRL, CQ, etc.; Are you listening?

The Trans-Oceanic Project

If you're reading this, there's a pretty good chance that you've got a soft spot for Commander MacDonald's baby: The Zenith Trans-Oceanic.  I certainly do: When I was about eight years old, my family took holiday at a cabin on Hubbard Lake in rural Northern Michigan.  At that time, there were no TV stations covering that portion of the state, but the cabin came equipped with a glorious model G500 Trans-Oceanic, and the sounds that came from it made enough of an impression on my pre-adolescent psyche that I became obsessed by all things electronic.  Eventually, this hobby became a career in radio from which I recently retired after close to 40 years.  Soft spot indeed.

Earlier this month, while on vacation in Florida with my wife and friends, I came across this very neglected model G500 at an antique festival.  The picture above really doesn't do it justice - this thing was totally trashed; the famed "Black Stag" covering was torn in several places and appeared to have been gnawed on by mice, as had some of the wiring.  The hinges for the rear panel had rusted completely through, the cover being held in place only by the rusted spring clips.  And the smell... Trans-Oceanics have a unique, friendly aroma, but this was a different fragrance: Mildew, rotted wood and mouse pee. 

But, the set appeared complete, including the coveted 1L6 converter tube, and the seller was willing to deal, so we agreed on a very low price (a fraction of what the airline charged me to check it as baggage) and the derelict became mine.

Things didn't get any better when I returned home and got the set on the bench and found that someone who should not be allowed anywhere near a soldering iron had attempted to repair the radio.  The underside was covered in soot; the power-supply section had lost its magic smoke in a big way.  My heart sank thinking about the rather delicate 1.5v tube filaments.  Had they also been damaged?    If so, my equity in this set would be in the red.

 

Fortunately, when I measured across the filament string, I got a nice, low resistance.  Holy crap, had the tubes survived?  I had to know!  So, I started undoing the previous work to see what all was wrong.  

My theory is that someone attacked the set based on "internet knowledge" that says selenium rectifiers are ticking time bombs, but without the understanding of what the rectifier does or how to replace it.  Equipped with this lack of knowledge, they bypassed the selenium with a silicon diode.  That probably went OK, but things went awry when they got to the filter capacitors... I'm not sure exactly what went wrong, but it's obvious that something was dead-shorted to ground at the input to the "candohm" resistor, vaporizing the diode and dropping resistor but not damaging anything else.  So, while it must've gone up in a glorious shower of sparks and smoke, the carnage was surprisingly minor.

Ironically, the selenium rectifier checked good, so the carnage was totally unnecessary.

Carnage removed.

New parts, including 1N4007 diode, mounted to added terminal strip.

Once the damage had been, um, rectified, the rest of the electrical restoration was uneventful.  The electrolytic and "Bumble Bee" capacitors were all replaced, as was the 3V4 audio tube, and the set roared to life.  Success!

But, cosmetically, the radio was a mess, and the only way to deal with it was going to be to strip it of it's upholstery, repair the damage, and recover it with new Tolex.  I wasn't looking forward to this part; I've seen reupholstered TOs before and you could immediately tell that they weren't original by the grain of the Tolex.  So, I scoured the web until I found a pattern that, at least in the photos, looked passable, so I ordered a couple of yards of "Black Bronco" from Parts Express.  When it arrived (in a very large box!), I was stunned - it was nearly a perfect match!

Thus, I set about the task at hand, photo-documenting every flap and fold of the old material as I removed it, and using each piece as a pattern from which the new pieces were cut.  Then, each piece was reinstalled exactly as the original had been by the factory.  Well, all but one - I goofed.  Still, it looks OK so I may leave it.

In addition to replacing the fabric, I polished and relacquered all the brass bits and installed a replacement dial lens (from Mark Palmquist - Excellent!), gave the set a final alignment and buttoned it all up.  

 Was it worth the effort?  Not economically, but I can't put a price on the rewarding feeling I got from bringing this beauty back from the brink. 

I'm still as enamored by these radios as I was back in 1970, they really are fantastic pieces of radio history.  It's unfortunate that so many international broadcasters have abandoned shortwave, but there's still a lot to tune in and nothing better to do it with than a Zenith Trans-Oceanic.

For anyone interested in learning about these sets, I highly recommend Bryant and Cones' book The Zenith Trans-Oceanic: The Royalty of Radios  from Schiffer Publishing.  It may be out of print, I don't know, but used copies are readily available through Amazon.  But please, don't be like the previous owner and attempt to service your TO without understanding what you're doing!

Philco 42-327T: Closure

It's been a couple of busy months, but the old Philco is done.  Once I repaired the damage I inflicted on it by foolishly lifting the cabinet by one of the grille bars, everything went together rather smoothly and it turned out quite nice.

I don't think I mentioned the chassis in any of my earlier posts, but it's rehab was relatively uneventful, mainly because nobody'd tried to fix it before I got my meat hooks on it.  So, it was simply a matter of replacing the electrolytic and paper caps, cleaning and lubricating the controls and tube sockets, and a final touch-up on the alignment.  The only thing that put up any sort of fight was the pushbutton presets, but that was just because they were full of crud and took some extra cleaning before they worked reliably and noise-free.

Performance wise, it's competent but not spectacular, as one would expect from a mid-low end radio.  The internal loop antenna works OK for the local stations, but it really comes alive when connected to an outdoor wire antenna, particularly on the shortwave bands. 

So, was it worth the effort?  Probably not from the financial perspective, though I don't have but maybe $50 invested in the thing and shouldn't have much trouble breaking even.  From the standpoint of personal entertainment, though, it was more than worth it.  Breathing life into a radio that's been neglected and dormant for decades is almost as much fun as building one from scratch!

One more time...

I made a stupid, bone headed move shortly after the last entry in this saga:  I was cleaning up and, rather than make multiple trips, carrying stuff from the garage to my basement workshop, tried to take it all at once.  So, I had my arms pretty well full, and grabbed the newly finished, nearly perfect cabinet by one of the grill bars (removed in the above photo) and it broke off.  Of course, it couldn't have broken off cleanly at a glue joint.  No - the glue bond holding that bar to the veneer was stronger than the veneer was bonded to its substrate, so about a three inch section of veneer peeled away and remained attached to the bar.  Crap!

I made a couple of failed attempts at "spot repair" before stripping it down to what you see above.  The good news is that the veneer patch turned out great - probably the best I've ever done.  The bad news is that I'm back to ground zero and into the second week of a project that should've taken just a couple days.  Oh well.

Haste makes waste.  The good news is that, this time, my lazieness only cost me some time; the damage is repairable and it's not a total loss.  The bad news is that, once this project is a memory, I'll probably make the same mistake again.  That's how I roll.

Almost Instant Gratification

Once the grain filler has cured, I give it a wet sanding with #400 grit.  After cleanup, the cabinet is nearly perfectly smooth.  If this were a more valuable set, I'd probably repeat this step until it was absolutely perfect, but this is a pretty common radio and the law of diminishing returns applies.

This set had what I'd call a 2 1/2 tone finish; the dial escutcheon and grille bars look to be neary black, while the trim along the bottom was a very dark brown.  I don't know if that was intentional or the result of nearly 80 years, but I'm going to stay as true as I can to that.  So, after sanding, I mask all of the cabinet that isn't going to be black or dark brown:

Then, before I apply the "color", I give everything a quick blast with clear.  I discovered, by accident, that this will seal the masking lines and helps avoid the color leaking in to where I don't want it.  

Being a low-budget operation, I don't use any sort of computer to match colors, I just have a variety of dyes in shades of brown, red, yellow and black, and match by experimenting, noting the how many drops of which go in to how many ounces of lacquer and the ratio of the lacquer to thinner.   Once I get a test spray in the tone I want, I note the "formula" for the next time, but I have to admit that I don't often refer to my notes anymore; I've done enough to where I "kinda" know what'll work.

Since this has the two dark colors, I first mix six ounces in the dark brown and spray away, two coats gets me to the color I want.  That barely uses an ounce, so not being one to waste material, I add black dye to the mix until it's, well, black, and spray the escutcheon only, being careful not to spray the black on to the fresh dark brown. 

Lacquer dries quickly, so it isn't long before I'm able to remove the masking and start adding color to the rest of the cabinet.  I mix the dye with the lacquer as before, but not adding so much dye that it becomes opaque, I go for a sort of weak coffee looking mix that takes a few coats to get to the final color.  This is where the instant gratification sets in, because as soon as that first coat goes on, the thing starts looking more like an old radio and less like a pile of junk.

And that's enough for tonight; clean the tools and put 'em away.  

It's amazing, with these projects, how much time you spend waiting for things to dry.  Actual work time spent so far?  Maybe a couple hours, but it's spread out over five or six days.  Anyway, I suppose I'm commited deep enough into this radio that I HAVE to fix the chassis... That'll be another installment in this saga.

More Cabinet Work

Work on the Zenith continues, and I'll detail that in the future.  For now, I thought I'd take a diversion and go through the steps of refinishing something less ambitious: A derilict Philco 42-327T that's been in my way since the spring.

Unfortunately, I didn't start the project with the intention of "blogging" about it, so I didn't take any "before" pics, nor any of it being stripped.  I think I can describe that, though:

The finish on the cabinet was quite rough, appearing as though it had been left out in the rain and then dragged, face down, across concrete.  Fortunately, the grille bars took most of the damage and the veneer was largely spared; other than a few chips and a bubble or two, it was pretty much intact.

So, to start, I carefully removed the grille bars, stripped them, then sanded the damaged sections while trying to maintain their original radius.  At the same time, I chemically stripped the cabinet, patched the damaged veneer and glued-up a couple of loose joints, clamping everything and allowing it to dry overnight.

This morning, I gave everything a "scuff" with 220 grit paper, then took it out to the garage and shot it with sanding sealer.  The pic below shows the cabinet and grille bars with the sealer just starting to dry.  The white portions are where I shot the sealer thicker than I should have, some of which was intentional.  These will become transparent as the sealer cures.

I'll let this dry overnight.  Tomorrow I'll tackle the fun-filled process of filling the pores in the wood and prepping for it's lacquer finish, which, once completed, will be as near to glass-smooth as I can make it.

Part II: Filling the grain

Well, normally I'd have let the sealer dry overnight, but with the temperature in the garage hovering around 100 degrees F, it dried very quickly and was ready for the next step in just a few hours.

At this point, the grain and pores have been sealed, which basically means that the wood isn't going to drink the lacquer that I'll eventually be applying, but the wood still is far from smooth, and if the top coat were applied at this point, each pore would "sparkle" as light reflected from the tiny pond of lacquer within it, making the surface appear rougher than it actually is.  The easiest way to avoid this is to use a commercial grain filler.

Now, grain filler is NOT the same as the wood filler sold at the big box stores - that stuff is to patch gouges and larger blemishes.  Grain filler is a bit different, it has a consistency that's a bit thicker than pancake batter, and is actually rubbed into the surface of the wood rather than brushed on to it.  Generally, you apply it against the grain with a plastic scraper, I find old credit cards work great for this.  Some people will rub it in with something like burlap.  I don't know about you, but I'm not exactly swimming in burlap, but have a seemingly endless supply of expired charge cards.  Like they say in amateur racing: Run what'cha brung.

Before I apply the grain filler, though, I sand the cabinet again using 220 grit to remove any excess sealer.  Since we're ONLY sanding the sealer and not the wood, I usually go across the grain at this point; I think it works better, but your mileage may vary.

After sanding across the grain with 220 grit.

After sanding, I scoop a glop of the grain filler from the container and push it across the grain with the aforementioned credit card.  In this case, I used a Discover that expired in 2005, but I don't think that matters.  What does matter is making sure that you actually press the filler into the pores rather than dragging it across them.  Think of buttering toast, where you're not so much spreading it across the surface as filling the voids with artery-clogging goodness.  Same basic idea, but with one difference: You don't want to leave any excess - the stuff dries like iron - so the motion is  a push and a scrape... Hard to describe, easy to do.

After filling the grain.  Notice that the surface has become reflective, it'll be more so after I wet sand it later.  The tub in the foreground is the grain filler, and, of course, my long expired Discover card.

A couple of comments about grain filler:  There are basically two types: Oil based and water based.  Some folks say that oil based is easier to work with due to it's longer drying time, but I've used both and haven't noticed a difference.  Expirement.  Also, I'm using a transparent filler here (Acqua Coat), but I've also used tinted and tinted my own to suit the type of wood I'm working with.  Again, expirement and see what works for you.

Also, I can't mention enough that you want to scrape off as much excess as possible before the filler dries. We're not going to be using any more coarse sandpaper, and you can develop tendonitis trying to sand smooth filler boogers with 400 grit...

So, now we're back to the exciting practice of waiting for stuff to dry.  Don't rush this step, else you'll have a mess on your hands when you start wet sanding, which is the next step.  Riveting stuff.  Stay tuned!

Zenith Chairside: On to the cabinet repairs

 Since it's nice outside today, rather than hole-up in the basement, I dragged the chairside cabinet out to the deck to start on the cabinet repairs.  The cabinet overall is in fair condition; structurally sound but with some minor damage.  The greatest damage is to the front of the speaker grille, where, somewhere in it's life, this radio got whacked hard enough to crack the horizontal bars and chip-out a chunk of veneer.  To start, I'll repair the structural damage by injecting glue into the cracks.

I inject the glue into the crack until it oozes out from everywhere along the crack where it can ooze.  Then, I'll pull it back into shape by clamping the damage between two flat planks of scrap wood.  This will force more glue out of the cracks, but I'm not going to worry about that now...

 I try to get as many clamps around the damage as will fit. Since I don't have many with jaws narrow enough to fit through the grille slats, I augmented my bar-clamps with a carriage bolt/nut threaded through the slats and clamping blocks.  Everything is synched-up tight and will be allowed to dry overnight. With any luck, by this time tomorrow, I'll have s straight grille panel needing only a small repair to replace the missing chunk of veneer.

While waiting for the glue to dry, I put the finishing touches on a Detrola 101 that I've been refurbishing at the same time as the Zenith.  This one also had minor veneer damage but without missing pieces, so it went through a similar repair: using a razor, I enlarged a pore in the veneer above the blister, injected it with glue and clamped between flat blocks.  After sealing/grain filling and spraying with toned lacquer, the repair is completely invisible.

Before: Presentable, but tired.

After.  Came out nice, no?

Zenith Chairside - Capacitor Madness!

Look at that flywheel!  That's what gives these old Zeniths their smooth as silk tuning. 

Normally, I follow a logical troubleshooting process rather than simply replacing parts wholesale, but not when it comes to the paper caps in old radios.  Why?  Experience has taught me that, if they're not bad now, one is bound to fail shortly after putting the set back into service.  It really stinks when you have to reopen a freshly completed radio to replace a $0.25 part, so I prefer to just change them all and be done with it.

As you can see in the picture above, this chassis has quite a few of those little turds.  Fortunately, they're readily accessible for the most part, and things aren't as cramped on this chassis as they are on many others.  Should be an easy job.

Even though this is more a matter of just replacing parts than it is troubleshooting, I still have an order in which I tackle these things - one circuit at a time, beginning with the audio power amp, just as I do in my homebrew projects.  The shot above shows the new capacitors installed in the push-pull output amp and phase inverter circuits.  Before moving onward, I tested the radio after replacing the caps to make sure I didn't accidentally introduce any new problems. 

Something to be aware of about radios produced between about 1939 and the start of WWII is that the rubber insulation on the wiring often will crumble when you move it the slightest little bit.  This usually means carefully rewiring the entire set, not something I particularly enjoy doing.  Fortunately, this set doesn't have much of that sort of wire, so I'll just have to rewire the harness for the eye-tube (shown below the volume control in the picture above) and a few other circuits, not that big of a deal.  Last year, I worked on a '41 Zenith and had almost 40 hours into rewiring the thing.  That's why I usually avoid radios built during that time frame, but this one is so damn cool that I had to have it!

Here's a tip:  I use welding clamps to secure the chassis to the bench while working on it.  The heavy power transformer is at the top of the chassis in this position, and if you don't secure it, the chassis is going to want to roll over and break some tubes.  A chassis stand might be a better idea, there's a fellow in Alaska that makes some nice ones, but I'm cheap and the welding clamps work well enough for me.

You can probably tell that I'm struggling to find something interesting to say about this stage in the process.  Changing capacitors isn't the most exciting thing in the world, but to me, it's cathartic:  I put on some music, pour a cold beverage and relax while plugging away at it.  

Here are some common questions that I'm asked:

"I can't find .05 uF capacitors anywhere.  What do I do?" 

• Use the nearest modern standard value:  For a .05, a .047 will be fine.  Likewise, .022 and .033 can be used to replace .02 and .03 uF.   

"This radio uses capacitors rated at 200 Volts, can I replace them with 630 volt caps?"

• Yes, you can always go to a higher voltage rating, but never go lower.  In most cases, modern capacitors will be smaller than the originals, even when the working voltage is much higher

 "Where do you get your capacitors?"

• The film caps that I use to replace papers are from Sal Brisindi at Sal's Capacitor Corner (www.tuberadios.com/capacitors.)  What I like about Sal's caps is that the leads are longer than others, so you don't need to do a bunch of splicing to get them to fit.  Don't ask me where they're made - the guy's name is Sal and he's from New Jersey. I don't ask questions, Capisce?
• I use Nichicon electrolytics that I order through Mouser.  

That's about all that I can muster to say about this topic.  See you next time!

New Project: Zenith 10-S-442 Chair-Side Console

I imagine that I'm like most people in that my radio production drops off during the summer.  In the winter, it's easier to hole-up in the basement building and repairing things, but I can't help but feel guilty doing so when it's nice outside.  So, summertime tends to be more of a time for acquiring things than it is working on them.  It also seems to be when the best shows and auctions take place, so I'm OK with that.

Last weekend, my wife and I attended the Michigan Antique Radio Club's Vintage Electronics Extravaganza, where I was able to add a couple more projects to the queue, including this 1940 Zenith Chairside.  I've been looking for one for about 15 years, and this is the first one that I've found that wasn't trashed or out of my price range, so I jumped on it.

This set appears to be basement fresh, still with all of its original tubes except for the notorious 6X5 rectifiers, which have been replaced with the later GT style.  The cabinet is solid, but in need of some veneer repairs that I'll cover in a future post.   For today, I'm going to go into how and where to start on something like this.

First, I'll start by removing the chassis and speaker from the cabinet so that I can get this thing from the garage to the basement without wrecking my back.  The next two pictures show the chassis, as found, from the front and rear.  It's surprisingly clean for something that probably hasn't been dusted in almost 80 years!

So, where do I start?  Well, in the past, I've found that some Zeniths from this era tend to eat power transformers, so before I get too far along, I ought to check this one to see if I need to source a replacement.  We'll start by replacing the power cord, since this one's has been cut-off - something I love to see because, in my experience, most of the cut-cord sets that I've come across didn't have any serious problems and, better yet, haven't been boogered-up by someone who tried to repair it without the requisite knowledge and skills.

The above picture shows the new cord and power-line filter capacitor.  The domino-shaped capacitor on the bench in front of the chassis is NOT a reliable mica, but what's called a Micamold - a paper cap disguised as a mica.  The give away is the value: .005 uF; generally, real mica caps will be .001 (1000 pF) or less.  The replacement is a .01 uF disk rated to be used safely across the power line, or, as in this set, from line to ground.  In this application, there is no benefit to sourcing a .005 (.0047 in today's parlance), a .01 will work fine and I've got them on-hand.

Next step is to pull the rectifier tubes.  This disconnects the transformer's high-voltage secondaries from the rest of the chassis for the next test - apply power to see if the transformer is transforming.

So, with the transformer effectively isolated, we can fire up the chassis using a current-limited, isolated supply.  This is a low-tech bit of test equipment; an isolation transformer with a 40 watt incandescent bulb in series with the chassis.  If there were a short in the chassis, the bulb would glow, dropping the bulk of the supply voltage and hopefully limiting further damage.

When measuring an unknown, potentially high voltage, I use my disposable Harbor Freight digital meter.  I've smoked two expensive meters doing this in the past, so now I use one of these until I'm certain that the voltage being measured can be handled by my Fluke or Simpson.  I also connect the meter, using insulated jumper leads, before applying power.  Why?  That's 607 Volts, kids.  Respect it, it can kill you.

Great news!  I've got the expected voltage on the secondaries - the transformer is good, the bullet's been dodged.

So, moving on, it's a virtual guarantee that the power supply filter capacitors have failed, so we'll disconnect power and change those.  Now, on models where the filters are mounted above the chassis, I'll remove the filter "can", remove it's guts, replace them with modern caps, reseal the can and reinstall it for an invisible repair.  In this case, the filters are in a cardboard tube below the chassis, so I'll remove this and replace it with modern capacitors mounted to a terminal strip.

The filter "can" is riveted to the chassis, here I'm carefully drilling-out the rivet.

I drill the rivet to the point where I can drift it through the bracket/chassis with a small punch.

Here, I've attached the new capacitors to the terminal strip before installation - it's easier to do it now than after it's been installed in the crowded chassis.  Teflon tubing insulates the flying HV lead.

Here they are in their happy new home.  I used the hole from the original "can" to mount the terminal strip, using #6 hardware - including lockwashers - you don't want this thing to move!

So, at this point, the smart thing to do would be to remove all of the remaining tubes, reinstall the 6X5s, apply power and test to see if you've got the expected DC voltages.  But, I'm a gambler, so I plugged the 6X5s in and fired the thing up, watching for smoke.  I must be living right, because the damned thing came to life, sounding great!  But, I didn't leave it powered on for long because it still has all of its original waxed/paper capacitors, some of which are likely to be bad or on the verge of failing.  So, the test was a brief two or three minutes of glory.

After the successful test, I started looking for potential signs of problems, and found two:  The RadioOrgan board was cracked and the insulation on the wiring at the base of the eye tube was starting to disintegrate.

Cracked RadioOrgan board.

Disintegrated wiring at eye tube base.

I'm not in the mood to deal with the wiring today, so I'll finish up for the day with the easy fix:  The RadioOrgan board.  This gets cleaned and reattached using "super glue".  The key is clamping it and leaving it alone for at least an hour or two so that it can fully cure.  Don't rush this and it'll turn out fine!

That's all for today.   Next time, we'll tackle the eye tube, including the pesky 1 megohm resistor, located in the socket, that's always bad. I haven't had much luck with eye-tubes themselves, they always seem to need replacement.  Fortunately, this set uses the fairly common 6U5 and not the rare and insanely expensive 6T5!

More Arduino: A Simple Iambic CW Keyer

I've been using the homebrew "TO" style keyer that I described in earlier posts for several months now, and I have to admit that I don't very much like it.  It also reminds me of why I ditched my Hallicrafters TO keyer over 30 years ago:  They don't support iambic mode and are a bit "fiddly" when compared to Curtis-based keyers.  So, I'm working on a replacement that uses the cheap (<$5.00) Arduino Pro-Mini board.

While scouring the web in search of ideas, I came across Ernest, PA3HCM's Simple Arduino Keyer project and was quite impressed, not only by how well it works but by how short and simple his code is.  Bravo, Ernest!

Of course, not being able to leave well enough alone, I had to add a few creature comforts: Adjustable weighting and sidetone frequency.  Ernest's code made that easy enough to do - the timing is based on the value read from the speed pot and the frequency of the sidetone, so with a little bit of manipulation, I was able to modify the code to add a "correction factor" that allows the weight or tone frequency to be changed without affecting the code speed.  It works well, and unlike the old-school "TO" based design, is very forgiving of operator induced timing errors.

Here's the code:

// Simple Iambic Keyer Mod0b3 by N8NM
// Based on the excellent work of Ernest PA3HCM
// May 23, 2018

/*
   Revision History:
   Mod0b0 - Initial build by Ernest PA3HCM with Arduino Pull-up resistors enabled
   Mod0b1 - Added PTT output functionality
   Mod0b2 - Added WEIGHT control, range: 2.25:1-3.75:1
   Mod0b3 - Added TONE control to adjust sidetone freq. Strap to 3.3V line if not using this feature.

   Controls:
   Speed: Sets element length (determines words per minute)
   Weight:Varies dash/dah ratio +/- 25%
   Tone: Adjusts sidetone frequency

*/

#define P_DOT     2                   // Connects to the dot lever of the paddle
#define P_DASH    3                   // Connects to the dash lever of the paddle
#define P_PTT    11                   // PTT output to radio
#define P_AUDIO  12                   // Audio output
#define P_CW     13                   // Output of the keyer, connect to your radio
#define P_SPEED  A0                   // Center pin of SPEED pot
#define P_WEIGHT A1                   // Center pin of WEIGHT pot
#define P_TONE   A2                   // Center pin of TONE pot (strap to 3.3V for fixed freq.)

int speed;                           // Declare variable used in reading speed pot
float weight;                        // Declare variable used in reading weight pot
int tone_val;                        // Declare variable used in reading tone pot
float loop_delay;                    // Declare variable used to calculate audio tone loop delay
unsigned long startMillis;           // Declare variable used to determine PTT delay
unsigned long currentMillis;         // Declare variable used to determine PTT delay
byte PTTSTATE = 0;                   // Declare variable used as PTT status flag

// Initializing the Arduino
void setup()
{
  Serial.begin(115200);               // open UART serial port at 115200 bps
  pinMode(P_DOT, INPUT_PULLUP);       // Enable DIT input with internal pull-up
  pinMode(P_DASH, INPUT_PULLUP);      // Enable DAH input with internal pull-up
  pinMode(P_AUDIO, OUTPUT);           // Enable output for sidetone audio
  pinMode(P_CW, OUTPUT);              // Enable output used to key radio's CW line
  digitalWrite(P_CW, LOW);            // Start with key up
  pinMode(P_PTT, OUTPUT);             // Enable output used to key radio's PTT line
  digitalWrite(P_PTT, LOW);           // Start with PTT off
}

// Main routine
void loop()
{
  speed = analogRead(P_SPEED) / 2;                     // Read the keying speed from potmeter
  weight = (analogRead(P_WEIGHT) * .001465) + 2.25;    // Read the character weight from potentiometer
  tone_val = analogRead(P_TONE) + 330;                 // Read the tone value from potentiometer
  if (!digitalRead(P_DOT))                             // If the dot lever is presssed..
  {
    keyAndBeep(speed);                                 // ... send a dot at the given speed
    delay(speed);                                      //     and add a space following the dit
  }
  if (!digitalRead(P_DASH))                            // If the dash lever is pressed...
  {
    keyAndBeep(speed * weight);                        // ... send a dash at the given speed
    delay(speed);                                      //     and add a space following the dah
  }
  if (PTTSTATE == 1)                                   // If PTT is active...
  {
    currentMillis = millis();                          // ... get the current time
    if (currentMillis - startMillis >= 1000)           // ... and if more than 1000ms has elapsed since last element was sent
    {
      PTTSTATE = 0;                                    // ... clear the PTT flag
      digitalWrite(P_PTT, LOW);                        // ... and release PTT
    }
  }
}

// Key the transmitter and sound a beep
void keyAndBeep(int speed)
{
  PTTSTATE = 1;                         // Set PTT flag
  digitalWrite(P_PTT, HIGH);            // Activate PTT
  digitalWrite(P_CW, HIGH);             // Key down
  for (float i = 0; i < (speed / (tone_val * .002)); i++) // Beep loop
  {
    digitalWrite(P_AUDIO, HIGH);        // Set audio pin HIGH for 1ms
    delayMicroseconds(tone_val);
    digitalWrite(P_AUDIO, LOW);         // Set audio pin LOW for 1ms
    delayMicroseconds(tone_val);
  }
  digitalWrite(P_CW, LOW);             // Key up
  startMillis = millis();              // Start PTT "hang timer"
}

And here's the circuit diagram:

The pot values aren't critical, though linear taper pots should be used for the speed and weight controls and audio (log) taper for the tone and volume.  I'm using 1K, since that's the first thing I grabbed.

Presently, I've got the keyer built on a solderless breadboard, and other than the occasional intermittent connection, it's been a joy to operate.  My Irish/Polish/Catholic ancestry has left me with no natural sense of rhythm, and it's able to mask most of my sending errors!

73 - Steve N8NM