New Restoration Project: 1940 Hallicrafters S-20R
 

Some of my fondest childhood memories are of the holiday gatherings at my Uncle Walt’s and Aunt Eleanor’s house on Nottingham Street in Detroit. The strong scents of roasting turkey and ham got stronger as I ran down the curved basement stairs to get my holiday hugs. My attention would quickly shift, however, to Uncle Walt’s Hallicrafters S-20R short-wave radio, standing just above my eye level. It certainly didn’t look like any transistor radio I was familiar with. This unit had tubes, and took a minute to warm up before gradually revealing people speaking strange languages. To me, this radio was magical.

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Hallicrafters made radios in Chicago starting in 1932. Based on the serial number of Uncle Walt’s unit, this specific radio was likely built around August of 1940. It’s interesting to compare 73 year old electronics with the modern semiconductors in today’s devices. Fortunately, I have the necessary schematic diagrams and tuning manuals to guide me. It’s interesting to see the tubes inside the radio, and I’ll likely have to replace a few of those, but the real work will occur under the chassis, where most of the original electronics will need to be replaced.

Look at the World War II-era advertisement of the S-20R below – talk about scaring your customers! I think the advertisement says “Sure, your church and neighborhood will be bombed, but your Hallicrafters radio will survive.” This thing is heavy and built like a tank, so that might be true. I’m sure war time broadcasts were heard on this radio.

http://upload.wikimedia.org/wikipedi...licrafters.jpg

I’m still in the research phase, but here’s what I know so far:

1) The original battleship-gray enamel paint is in good condition and will be left as-is.

2) The power cord and speaker appear to have been replaced at some point, I will acquire the proper size and type of speaker and cloth-covered power cord to make it period-correct.

3) Some tubes will need replacement, but interestingly are still available.

4) All capacitors will be replaced. These semiconductors were built around a paste-like material that dries over time.

I will provide updates here as progress is made. This should be an interesting restoration project.

A view of the interior from the top:
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This speaker mounted to a hunk of plywood appears to be non-original and will be replaced:
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Below the chassis, most capacitors will be replaced
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Too cool...

That is awesome!

The 1940 Hallicrafters radio restoration project has already been quite interesting. Like an old motorcycle, old radios were often modified by their owners, and this radio was no different. The toggle switch at the upper right of the radio was added at some point. Other wiring modifications were made to the rear of the chassis. The radio case can no longer be considered “original”, but that now frees me to repaint the unit. I’ve ordered a set of reproduction lettering for this exact unit, and will sand, prime and repaint the unit in the original color. The hole that was drilled in the case for the non-original toggle switch will be filled with an epoxy to return the case to its original appearance.

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I’ve already ordered 77 new parts so far, including modern replacements for the ancient electrolytic and paper capacitors. I’ve ordered replacements for all 9 tubes, although many of the originals are still likely to be good. The tubes were inexpensive. The tube in the picture below is a full-wave rectifier. Even the 4 rubber feet are being replaced since the originals are as hard as a rock.

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The wiring will be corrected to match the schematic using period-correct cloth-insulated solid wire. I’ve noticed tiny hand-written paper tags on many of the wires from the original owner. That adds a bit of charm, so I will retain those tags.

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The chassis was quite dusty, so I removed as much dust as I could with compressed air. I’ll clean the chassis with a small brush, which will be tedious work. I’d like to avoid touching the dial cords and pulleys as much as possible. The dial faces are made of phenolic resin, which oxidizes and reacts to UV light, turning an orange-brown over time. I have cleaned the dial faces and will retain the originals.

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The work on the chassis and the replacement of the electrical components will begin in early December.

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MAd SciEnce!

No Longer Available

You just HAD to take it apart didn't you? :D

Chip, glad to hear that this old radio brought back some memories. My preference is to have projects that I can license and ride afterward, but this is a huge challenge. My electronics experience is 40 years too new for this unit, so I've been doing lots of research to understand the operation of the tubes ('valves' for Sam Green and my UK friends), and even identifying standard parts can be a challenge at times (I had never encountered 'dogbone' resistors or paper capacitors before).

Ryan, I had to take it apart - most of the capacitors, and some of the resistors and tubes, were shot. Funny, just like old motorcycles, I'm learning that amateur radio guys often modified their radios, so I've encountered some customization. Since this radio was modified, it's no longer in original condition, so that frees me to fill the holes, re-paint the case, and apply reproduction lettering to restore the case to a near-original appearance.

I have hours of soldering work ahead of me, but I’m in no rush. I’m still waiting for the replacement tubes to arrive. To maintain the proper vintage appearance inside, I've ordered new cloth-insulated wiring to replace some broken or cut wires.

The chassis after an initial cleaning:
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Filled a hole with JB Weld:
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Replacement resistors:
http://www.forths.com/blog/wp-conten...rsDSC05003.jpg

Replacement capacitors:
http://www.forths.com/blog/wp-conten...rsDSC05007.jpg

Replacement socket and retainer to restore rear of chassis to original condition:
http://www.forths.com/blog/wp-conten...rsDSC05015.jpg

Cloth-covered power cord and support grommet:
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With Christmas behind me, I’m making some progress with the radio restoration project. I’ve replaced about 3/4 of the 73 year old components, but still have about 6 hours of wiring work left to do. Out of curiosity, I’ve tested each original component that I’ve removed to see how close to spec it is. Roughly half of the capacitors were no longer in spec, and most resistors were well out of the 20% tolerance margin. A few resistors had infinite resistance, so this radio would not have worked had I simply replaced the tubes.

I’ve also encountered parts that do not appear on the manufacturer’s schematic diagram. Judging from the solder joints, it’s clear that the radio was modified earlier. Considering the age of the extra parts, it was probably modified in the late 1940s or 1950s. Most of the non-original electronics are electrolytic capacitors, and based on where they were placed in the circuitry, I’m assuming that they were added to eliminate the “hum” that aging capacitors can cause with old radios, but that’s just a guess.

I wasn’t expecting a surprise from the vintage power cord, but as I removed some cloth insulation, it was clear that this cord was covered with felted asbestos. This was common in the old days for power cords that were used for devices that made a lot of heat or used a lot of power, such as irons. I disposed of any loose asbestos and cleaned the wiring.

Still have a lot of work ahead, but it’s fun and certainly an ongoing education.

These tubes have been tested and are ready for use.
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New felt washers will sit under each knob
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Vintage power cord is wrapped with asbestos – wonderful
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Original .05 mfd paper capacitor at top, with the replacement .056 mfd capacitor below
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Original 15k ohm resistor at top, with the replacement resistor below
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Original 10k ohm 3 watt resistor (top) with a replacement 10k ohm 5 watt resistor below
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Tough job keeping the smoke in those little things isn't it..... can't wait to the see the final project.
L

Today I repacked the large electrolytic filter capacitors. These are the 3 largest caps in the radio, and are packed into a single aluminum canister. The original specs are 30, 10 and 10 MFD, but currently test at 19, 10 and 0 MFD.

There are typically 2 options to replace these caps. First, I could simply disconnect this cap below the chassis and leave it in place, wiring in new separate capacitors below the chassis. A popular alternative is to disassemble the canister, discard the original guts, and repack it with separate electrolytic caps.

I decided to repack the capacitor for a number of reasons, but mainly because I wanted to avoid crowding parts together below the chassis, leaving me more room to work. I cut away the crimp at the bottom of the canister with a table grinder. The guts were as expected - thin layers of aluminum wrapped in paper that was at one time soaked in an electrolyte. The cap appeared to have signs of burning, perhaps explaining why one of the 3 showed infinite resistance.

Once the original wrapping was discarded, I cleaned the canister and bottom, drilling holes to allow the new leads to be soldered to the legs. Since I had axial capacitors, I routed a heavy wire from the negative terminal to the top to allow the 3 capacitors negative wires to be soldered together. The original caps shared a common ground too. The new caps fit snugly in the can, and it was sealed back together with silicone. The new cap tests good on all 3 leads now. When the silicone hardens, I'll remount the cap to the chassis and connect it back to the circuitry.

Electrolytic capacitor (3-way) before disassembly:
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The canister crimp is ground away:
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Original wrapped aluminum and paper interior:
http://www.forths.com/blog/wp-conten...rsDSC05147.jpg

New electrolytic capacitors are mounted on the base:
http://www.forths.com/blog/wp-conten...rsDSC05149.jpg

Capacitor is closed and sealed with silicone:
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Never seen THAT done before... excellent and preserves the 'look' or originality.
Well done...golf clap....
L

Re-stuffing capacitors is a fairly common practice with radio and amplifier restorers. I'm not a purist - under the chassis, it's all new capacitors and resistors.

Sounds like the "winter /inside projects" all you northerners talk about.
We're going out in the boat today (if the weather holds).... ;)
L

Larz, speaking as a "northerner" (but living in the south), winter projects are a must for those of us that need to remain active indoors. Many of my best memories are of winter evenings in the shop, listening to an AM talk radio program, NPR or just some old tunes. My best earliest memories were in the basement of my boyhood home in my dads shop, sometime in the middle of winter. To this day, I love the smell of single malt scotch, a good cigar and Hoppes Gun Cleaner.

BTL, I have to admit that I am impressed with your electrical knowledge regarding this old radio. I don't have the talent to do this type of project. When it comes to electronics....I am absolutely clueless.

It's going to be nice to wake her up again.