Sunday, April 5, 2020

BUILDING A 1:1 BALUN

     Having decided I need a 1:1 balun -- a kind of RF transformer, used to connect unbalanced (ground-referenced) equipment to a balanced device (like my G5RV antenna) -- I found a ferrite toroid core that seemed likely, wound two interwoven 12-turn coils of #14 house wire on it (as much as would fit), and looked around for an enclosure.

     I didn't have much, and then I found my collection of old tea canisters.  That worked.
     The coil is sandwiched between two 1/8" Garolite* plates held by brass screws (one headless) into a ceramic insulator; another, shorter insulator is threaded onto one end and fastened to the bottom of the box.  The lower plate has two corners clipped so the wires from that side can get to the terminals.
     There's a trick to working with such thin metal.  You can drill it, but it's risky -- even with a backing, it can catch and tear.  A better bet is to mark hole centers with a sharp awl and use a Roper-Whitney punch,† which will center up on the awl-made dimples.  Careful work with a hand reamer or chassis punch will enlarge the holes if necessary.  Small holes can just be punched with the awl, especially in places the punch wont reach.  (The lid does fit square, when properly seated.)

     My little SWR analyzer says it's not terrible on the 80 meter ham band and not bad on 40 -- the ferrite I used was supposed to be good through 30 MHz, but the match start getting worse and worse by the 20 meter band.

     Checked it with the RME-45 receiver and Millen "Junior" transmatch and it works okay, slightly better signals with it between the antenna and the matcher.  80 meters was a jumble of noise this afternoon.  Just went down (10:20 p.m.) and turned on the receiver; as I tuned past 3885 kHz, a voice came out of the speaker: "Hello, Bobbi!  C'mon Bobbi..." 

     That got my attention, as you might expect.  I dodged the slow-rate tuning back and forth a little, and he came back on, "[callsign], this is [other callsign], c'mon, Bobby, if you're not there I'll just call CQ, CQ, CQ , this is [othercallsign] and remember, people, don't buy coax jumpers, you build your own.  CQ, CQ, from [other callsign], c'mon..."

     So I wasn't hallucinating.  And I was certainly glad I'd made my own coaxial jumpers!

     Next step, rebuilding the transmit/receive switch and moving the DX-60 transmitter over to the new shelves.
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* As close to Bakelite as you can get now.  McMaster-Carr stocks it in a variety of sizes and shapes.

† Mine is actually a Whitney-Jensen, an earlier model with a few minor differences.  These useful little devices are widely available used. Plugging the name into a search engine brings up a lot of listings at online auction sites.

Monday, September 9, 2019

HERMES "ROCKET"

     It's a small portable typewriter.  One of the smallest ones, in fact.  Hermes has an excellent reputation, so when this one showed up at a reasonable price and supposedly in good shape, I leapt at it.

     Showed up and it didn't shift.  Shift keys didn't feel like they were even connected to anything, just moved loosely from one position to the other.

     In a larger typewriter, this is a long linkage and I figured it might have broken or fallen out.  I decided to open it up and see:
     Every key lever has an interesting scissors-looking linkage, just behind that flat shiny part with five screws in it. I think this arrangement gets them more leverage in the very short space available.  The two pieces for the shift keys had popped out of alignment, perhaps due to jolting in shipment.  I was able to work them back into place.  The fractions key had a similar problem and stuck when I tried it; getting it back took several minutes of careful effort.

     After that, I cleaned and lubricated where I could, and it's working pretty well.  Needs a new ribbon and it seems to not want to double-space, but still, I'm not unhappy so far.

Monday, February 15, 2016

T. R. MCELROY'S STREAMLINED TELEGRAPH KEYS

     T. R. McElroy was a blazing fast telegrapher -- any code, any time.  He worked both landline and radiotelegraphy, and set speed records.

     But he was ambitious, too.  In the 1930s, he started manufacturing semiautomatic telegraph keys of his own design, massive, heavy bugs that suited his own style -- and which appealed to plenty of others, too.

     The original Mac bugs were heavy, rectilinear keys with their own style, a little "Arts & Crafts meet heavy industrial" look.  But the times --and the styles -- were changing and shortly before WW II, Mac introduced a series of streamlined telegraph keys unlike any any other, culminating in the S-600 Super Streamspeed semiautomatic key, possibly the most graceful "bug" ever made.

     I own a few Mac keys and recently bought an accessory:
     There's an uncommon Bakelite-based Streamkey at far left, followed by a Telegraph Apparatus Co. (not Inc.) copy* of the wrinkle-finished metal-base Streamkey (you can tell by the bulge in the lever arm at the contact area) and a pair of chrome-plated McElroys.  The Streamspeed is at far right, and it handles just as fast and sleek as it looks.  At the very back, the accessory and its box: an Oscillatone code-practice oscillator.  They are not especially rare and this one was offered at a very low price -- how could I pass it up?

     Restoration will be interesting.  The Bakelite is likely to be very brittle.

     There are still McElroys in the electronics business.  They're not making telegraph keys any more, but the name lives on.
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* TACo was a co-venture between McElroy and Hallicrafters.  They built copies of Mac Streamkeys and their own interesting semiautomatic key, sometimes known as the "hole-in-the-wall" bug.

Friday, January 15, 2016

A VINTAGE-SUITABLE CALENDAR

     I needed a calendar for my mostly-vintage hamshack.  1932 and 2016 share the same calendar, but buying an old one in intact shape and ripping each month off seemed too destructive to me.

     So I made one.
     The backing sheet is card stock.  The calendar pages look crooked -- the paper fasteners that hold them are a bit loose in the punched holes.  It straightens out when hanging.  The printer output does not look like hand-set type, but might pass for offset printing or lithography.

     I'm trying to figure out how to post the original as a PDF, if any readers would like their own copy.

Sunday, July 12, 2015

INDIANAPOLIS HAMFEST, 2015

     I had to go solo this year, while Tam stayed home to meet the AT&T tech.  This meant, of course, that I lacked even the modicum of restraint she sometimes adds--
     The two large devices are a 1940s Meissner Analyst, which is a kind of "test bench in a box" for receiver servicing, and a 1950s Harvey-Wells Bandmaster, a 25 to 30 Watt AM/CW amateur radio transmitter.  Both appear to be pretty clean; the transmitter needs an external power supply, 400 V at 200 mA.

     Other neat stuff: a pair of vintage binoculars in good shape -- didn't have anything but toy versions, so for $35, why not? -- a very good push drill with straight bits and a "Handyman" Yankee screwdriver, a full set of Birnbach ceramic antenna insulators, chassis-mount octal plugs (good for power supply connections), three General Radio mixer knobs, a couple of Dakaware knobs, a National tube socket and 100 pF variable cap, another 100 pF dual variable capacitor, an SW-3 coil form, a 6F7 tube (possibly for a project) and a pair of 6L7s (used in my microphone mixer).  Plus four 1940s/50s QST magazines, three quartz crystals and and assortment of other nice small parts.  Not shown, a short (10'?) desktop rack and a large toroid core to wind a balun on (you want 'em big -- magnetic saturation is lossy and can produce a lot of heat!).

     I met my dear old friend Don H., and several other people I know slightly, including the talented Jim Borgioli,whose ham work includes building very nice AM transmitters that run at or near the legal power limit. And one ham who knew me!  A young man who'd gone looking for info on the Stancor 10-P transmitter and found my postings about it on Retrotchnologist walked up to in the flea market area, asked, "Are you Roberta?" and introduced himself.

     Found but missed a nice balanced antenna tuner.  I should have purchased it at first sight!  But it's a cloneable design and I think I have the parts.

     A fun time!  When I returned home, the phone tech was there -- and pointed out a very large broken limb on the roof and my ham antenna and still loosely attached to the tree.  I climbed up and had a look, but it's too big and too precarious for me.  We've called the singing tree hippie, who does great work at a fair price.

Monday, June 1, 2015

CARBON MICROPHONE CHECKING

     I went through most of my collection of carbon mics tonight.  The old ones are nearly always non-working when found: they pick up humidity, the carbon packs solid, and that's it; or the carbon granules dribble out over time. 

     Not all of them.  I found several that still work, and a couple that I'd thought were dead (a Shure Brothers 3-A and a 3-B) aren't.  Here are the working ones:
      Two are telephone-types, the T-32 (a pretty common desk mic around WW II) and an odd old telco one from the wood-wall and candlestick era next to it.  The Universal X1 in its nice stand was a complete surprise; I assumed from condition it was a goner.  Nope!  And the little Philmore lapel mic next to it had been sealed up.  The Stancor 10-P -- which needs a carbon mic to do AM -- is behind them.

     Here's my test set-up.  The mic cable goes to a little mixer.  It's isolated with 0.68 uF series condensers, looking at current across a 150 Ohm resistor in series with the mic, a 1.5 V battery and an added resistor to limit current -- I used 820 Ohms and it worked okay for checking.  In practice, you trim microphone current for best fidelity with a carbon -- usually the lower, the better, but there's a point where it stops working.
     Mic cable to mixer at left, connections to carbon mic under test at top right, battery terminals and added current-limiting resistor at bottom right.  I think you can trace it from the photo.

Thursday, March 26, 2015

STANCOR 10P TRANSMITTER: UPDATE 12

     A very long time in coming, I did make progress on the Stancor 10P, getting as far as power supply:

     Rectifier heaters and HV, filter caps, filter choke and bleeder.  It's a little crowded and I struggled to solder the capacitor and resistor to the chassis, even with the big iron.

     That work had it almost done, so tonight I added a few more things:
     Installed output feedthroughs and connected the output, wired up the primary power and the meter.

     Top view:

     Rear view:

     Front view:
     Initial tests -- just power-up, check for excessive current draw, check B+ -- went okay.  Hoping to try more by the weekend.

     Update: Tuned the transmitter up on 40m with a 100 Watt lamp in series, and it made a little power (4:1 balun to a Bird Wattmeter and 50 Ohm load.  Tried it without the lamp and blew the fuse instantly.  So....bigger fuse, and/or 150 and 200W lamps.  Maybe a little Amprobing..

     Update 25 May: Yesterday, I finally brought the transmitter up without a light bulb in series with the 120V AC and it worked. Last time I tried this with the wrong fuse (fast-blow) and it popped immediately -- at which point, I set the transmitter aside for awhile. I didn't have the balun and wattmeter for this test, just a 40W light bulb across the output, which is a bit low-resistance for the link coupling to match to. Plenty more to do but this was a big step.