This is a neat little gem that I found at my local antique shop for about $20 one Friday afternoon. Given the +A and +B terminals, I knew it was some sort of charger for antique radio batteries in the days before wall-socket powered radios became common. This made me think that it would be an interesting "accessory" addition to my growing collection of antique radios. I'm always on the lookout for something that is a little bit different or unique. Its overall condition wasn't too bad, despite the rust, dings, and scratches here and there. Thus began an interesting journey of dissection, cleaning, and learning.

After a little bit of research, I found a magazine ad from Aug 15, 1925 announcing the "next generation" of the Handy Charger from Interstate Electric Company. Looking closely at the image shows three positive voltage taps on the right hand side of the front panel, where my example has only two voltage taps. The second ad was printed on Nov 15, 1925. Thus, I can only conclude that the charger I have was made prior to the ones pictured in these ads, perhaps in late 1924 or early 1925.

Disassembling the unit revealed a missing Tungar rectifier bulb (two bulbs makes it a full-wave rectifier - hence the claim in the ad "...using both halves of the AC wave, assures a fast rate of charge...") and just a general level of dirt, dust, and rust throughout. The construction is relatively simple and very sturdy. 

The rusted "spring" in the back is a "reactance coil" that serves to help smooth the DC pulses that come from the rectifier tubes. Careful measurement reveals the following electric properties for the coil: Resistance of 1.3ohms and 22uH of inductance at 120Hz 

I worked on the chassis first. I was originally planning on just repainting it, but this left too many scars behind. So I ended up completely stripping the old paint, sanding down some of the high spots and starting all over again. I used some "Sandable Filler Primer" and applied a few coats, sanding between layers, until the surface was smooth. I then used a textured spray paint to add restore the original surface texture, then a layer of colored enamel on top of that. Finally, a few coats of clear enamel were applied to the top to help protect things. I used a wire wheel with my drill to clean up the handle, which appears to be nickel plated. 

The name plate on the lid was rather scratched and had small rust spots. I found a great technique on the Antique Radios forum that involved the use of "water slide" decals. I had never heard of these before and discovered a great opportunity to restore the name plate as well! I started with a high resolution scan of the original (a small version of this appears below). I imported the image to PhotoShop and then spent quite a few hours cleaning it up. The letters were darkened in, the edges were cleaned up, and I removed all of the scratches. I used my ink jet printer to print out the water slide decal and transfered it to the back of the original name plate. I found that Krylon colormaster paint + primer Brushed Metallic Champagne Nouveau Satin was an almost perfect color match to the paint on the front of the nameplate. After the decal was dry, I added a few coats of clear enamel to help protect it and found some new brass clips to reattach it to the charger lid. 

The black and white image above is a 1200 DPI label that you can use for your restoration project.  

Below are various images I made as things came apart, were cleaned, and then reassembled. The rust was removed with a combination of a wire wheel and some "Naval Jelly" rust remover. I used a set of clamps to hold the laminate stack together while I refinished the brackets. The transformer itself is quite substantial - I was surprised just how much it weighed.

The screws that mechanically hold things together were replaced with stainless steel screws of the same dimension and style. Every brass screw, washer, and nut was was cleaned. I replaced the three screws on the front panel that formed the voltage hook ups. These screws were capped with authentic vintage bakelite screw terminals. Soldering to brass, by the way, is a major pain. You need to get things VERY hot in order for the solder to flow and bond.

The transformer primary lead in wire is 16ga stranded and the primary has two taps: one for 110v and one for 120v. This is adjusted by moving the threaded nut on the top left of the ceramic bar. Filament secondary wire is dual run of 15ga (0.056" or 1.45mm) solid core, net 12g for current carrying capacity and the B+ secondary lead in wire is 25ga.

The transformer itself weighs 10 lbs. The overall core width is about 6 inches and has a height of 3.4 inches. The thickness of stacked laminations is about 1.2 inches and the laminate core that the wire is wound on measures ~ 1.25 inches by 1.25 inches.

The original 10A mica windowed fuse was still intact, it it, too was cleaned and reused. The cloth wires that connect to the tube clips were also replaced. 

I was able to source a replacement Rectigon bulb from ebay. The one original bulb was stamped with: "S-289415-B  W.E. & M. Co. U.S.A." which stands for Westinghouse Electric and Manufacturing Company. There are several varieties and sizes of these bulbs. "Tungar" is derived from Tungsten / Argon and is a trade name of General Electric. The Westinghouse trade name, sold under license from GE is "Rectigon" for Rectifier / Argon. Another, more generic, name for these bulbs is Phanotron.

The first vacuum tube diode for converting Alternating Current (AC voltage) to Direct Current (DC voltage) was invented by John Fleming in 1904. Tungar/Rectigon bulbs are among the earliest commercial form of a rectifier tube. Each one is a half-wave rectifier, though bulbs with two electrodes at the top are full-wave rectifier bulbs. This one is a medium base (or Edison Base - same size as a typical light bulb base today) and is rated to deliver 2A of current. The screw in base powers the filament and also provides the raw AC power signal to the bulb. The rectified DC voltage emerges from the wire at the top of the bulb where the spring clip attaches. Finding another bulb wasn't too hard to accomplish. Most of the ones out there are pretty old and the filment is rather sagged from hours of prior use. It's a rare treat to have the opportunity to purchase a new/relatively unused bulb. Below is a chart that I found in a PDF about GE Tungar bulbs indicating bulb wear:

Having the entire unit disassembled provided an opportunity to draw out a schematic diagram for the circuit. This took some careful measurment with a precision LCR meter and powering up the transformer with an 11Vac transformer and scaling up the voltag ratios. This avoided the need to play with voltages of uncertain level as I learned how this was wired. The +A terminal on the completed charger delivers 36vDC (with a 24v AC carrier) and B+ provides a fluctuating 31-33vDC (and 110v AC). The AC component in the voltages are likely to be a result of having no load attached to the terminals. Thus, the design of this charger would enable it to charge six 6-volt A+ batteries in series and one B+ battery at about 150vDC. While the A+ wires are nice and heavy, the B+ wire is extremely thin and I'm not interesting in putting a load on it to see how it actually behaves.

Using measured voltages, it is fairly easy to derive the turns ratios for the transformer:
If the primary has 240 turns, then:
The +B winding has 210 turns for (210/240 * 120) = 105v,
Each filament winding has 5 turns for (5/240 * 120) = 2.5v, and
and the +A winding has 48 turns for (48/240 * 120) = 24v.

Even the meter came apart so it could be cleaned. Metal flanges on the bezel allowed me to remove and clean both sides of the glass. What a difference! 

Cleaning up the face plate was the hardest part of all of this. It was badly pitted from rust. After rust was removed, I used primer+filler and put down a few coats and kept sanding until things were clean and smooth. Then came the black paint. I had the carefully scrape the black paint out of the grooves for the lettering before they would take some gold fill. I used "AMACO Rub 'n Buff " for the lettering. It's a wax that comes in Antique Gold - you spread some on your finger tip (or a Q-tip) and press it into the recesses. Before it starts to dry (you only have a few seconds), wipe away the excess. When everything was dry, the entire faceplace received a few coats of clear paint to help protect it.

3-conductor 16-gauge overbraid cotton cord from SunDialWire was a perfect replacement for the original, frayed cord. One conductor was unused, but the overall cord was the perfect diameter for the plastic insert in the front panel.

Finally, the original cord had a plug that screwed into a light bulb socket, not the traditional two-prong plug that goes into a wall outlet. The reason is simple: there were no wall outlets in the middle 1920s in the United States. If you had electricity (this is a big "IF" - the Rural Electrification Act did not happen until 1936), it was simply for a light bulb in the room. Thus, I found an authentic hybryd plug from the 1920-1930 time period. Pull the outer part off and it goes into a standard wall socket. With the outer part in place, it screws into a light bulb socket. So there you have it- an authentic, fully restored and functioning battery charger from 1924 or 1925. What a cool find at the local antique market!