All American Four!

I first saw this sad little radio at a yard sale. I think I paid $2 for it. Clearly it did not work, it was badly beat up, and ugly. I have a soft spot for neglected vintage electronics, so I bought it, brought it home, sat it on top of a book case and forgot about it. It sat there untouched, dirty, sad and ugly for nearly 25 years, progressing from merely old, to antique status.

     Then one day the restoration bug bit me, and I got it out and began to look at it with an eye toward fixing it up. I carefully cleaned up the case a bit, and took it apart, expecting to find a generic “All American Five” ( http://www.angelfire.com/electronic/funwithtubes/AA5-1.html ) design. The first thing I noted was that it used the older style Octal tubes. That marked it as pre-dating the 1950's when the AA5 was most popular, as many of those used a newer miniature style tube. There were AA5 radios that used the Octal tubes, but they were an earlier generation of design. Clearly then, this was a pre-1950 radio.

 

The radio as I first examined

it on the workbench

     The real shocker however came when I realized that there were FOUR tubes, not five. I had known that when the first solid state rectifiers became available using Selenium and not today's silicon, some AA5 designs had omitted the rectifier tube and employed a stack of selenium rectifiers, but this was fairly rare.

      Before continuing, let's give a brief overview of the basic superheterodyne radio and how it works. Wikipedia has an interesting and detailed article, so I will not reproduce their material. ( http://en.wikipedia.org/wiki/Superheterodyne_receiver ) Instead, let's just hit a couple of high spots along the way.

     The first practical Superhet radio appeared about 1918, thanks to the efforts of Edwin Armstrong, who was a Major in the US Army stationed in France in WWI. For various reasons, the Superhet design did not really become popular until the early 1930's, and by the mid-1930's the strength of the design had pushed competition aside and from that point onward, Superhet radios were the primary architecture used. One reason for the delay was that Maj. Armstrong sold his patent, RCA acquired it and used their clout to keep them off the market, and until that patent expired, general usage of the design was limited. RCA made a few, and a few others paid RCA to license the design, but until the patent expired most manufacturers were blocked from using the technology.

     The basic principle of the Superhet is that the incoming radio signal is converted to a lower frequency where it can be more easily and more consistently processed. This conversion process is called “heterodyning.” In an AM radio, the incoming frequency can be anything between 540 kHz and 1750 kHz. No matter what the station's frequency, it is mixed with a signal from a local source and the difference signal, or Intermediate Frequency is always 455 kHz, which is then filtered processed into audio. For example, to receive 700 kHz AM, a local oscillator produces 1155 kHz, which is then fed into a mixer along with the off-air signal. The difference signal is 455 Khz which is then processed by various circuits to render the audio. In radios prior to the advent of the Superhet, these various circuits had to tune and track each other to deal with the entire range of 540-1700 kHz, a difficult and inefficient prospect, but in the Superhet they are fixed at 455 kHz, and thus simpler and easier to align and keep aligned.

     The basic AA5 design used one tube as a combination Local Oscillator and Mixer, one tube as an Intermediate Frequency amplifier, one tube as a combined detector and audio preamplifier, and finally, one tube as the audio amplifier to drive the speaker. If you were counting along, you noticed that was FOUR tubes, not five. The fifth tube was used in the power supply, to convert the AC power from the power line into DC power suitable for running the radio. This process is called “Rectification” and the tube was called the “rectifier.”

     As I said, a few AA5 designs replaced the rectifier with a stack of selenium diodes, but this was fairly rare. The rectifier tube was relatively cheap while selenium was more expensive. It is also quite poisonous. Tubes were a better solution overall.

     My little gem had four tubes, but no selenium stack. Instead, there was a 35Z5 tube rectifier plainly visible. So this was a three tube superhet (plus rectifier) design. Most unusual. The little radio began to pique my interest as I researched its origins.

     It turned out that in the 1940's, a low-cost manufacturer named Noblitt-Sparks Industries, Inc. had a streamlined design that eliminated a tube. Noblitt-Sparks had started out manufacturing mufflers for Ford and Studebaker in the late 1920's. They also made a rear-view mirror. In WWII they were devoted 100% to manufacturing for the military. Post WWII they began to manufacture cheap radios, and by eliminating a tube stage and making others do double duty, they produced a significantly cheaper product, albeit at some slight sacrifice in performance.

     In 1950 they changed their name to “Arvin” and continued making cheap radios, heaters and other products. They had used the name “Arvin” in the 1930's as a brand name for a line of wooden cased radios, and resurrected the name in 1950 as the company name.

     On August 15, 1947 they began producing chassis # 132.838 for Sears Roebuck, and this well engineered but very inexpensive little radio was sold for model year 1948. Priced at $22.95 ($2.50 down and $5 a month), and there were a few variations, different color cabinets, and such. Sears sold quite a few of these little radios before replacing them with another model the next year. The shift to the miniature style tubes began soon thereafter and most 1950's vintage AA5 radios used them instead.

     In today's sensibilities $22.95 does not seem like a lot of money, and one might wonder about the emphasis on low cost construction. We lose sight of how much money has changed over time. In 1947, a first-class postage stamp was 3 cents, a loaf of bread was 14 cents, minimum wage was 40 cents per hour, and a wage for a typical laborer or office worker might not exceed $22.95 a WEEK. Despite the low cost, a radio was a very expensive luxury for most people. Every penny, every nickel counted! Selling for such a low price allowed many more people to afford them than might otherwise.

     This little radio had several remarkable features for its time. First, it uses a vernier mechanism for the dial, giving an unusually smooth tuning action. Verniers were hardly new, but finding this in such a cheap radio was unusual. A second uncommon feature was its “floating ground” design. AA5 style radios were known for the fact that the AC power line is connected to the chassis. This is a dangerous thing, as the chassis can easily be “hot” to AC. A missing knob or exposed mounting screw could become a serious shock hazard! Such a thing would not be permitted in a product sold today, but was common in that era. This radio was somewhat remarkable because the chassis was NOT connected to the power line, and there is no immediate shock hazard from any metallic part that one might inadvertently touch. Even if you remove a knob and touch the shaft directly, there is no shock hazard!

     A third, and also very important feature was the use of an “Antenna Hank,” a ten-foot-long piece of wire that hangs out the bottom, intended to be draped behind the bookcase or whatever, and to serve as an external antenna. At first this seems very odd. Modern AM radios use a “loopstick” internal antenna, a coil of wire wound on a ferrite rod. Radios of this vintage typically used a similar coil, but wound on a cardboard holder that was often the back of the radio. The problem is, this radio is too small for that, and loopsticks were not yet commonly used and would have been expensive for such a cheap radio. The “Antenna Hank” was an ingenious solution that (a) allowed the radio to be smaller, (b) gave better signal pickup than an internal loop, offsetting somewhat the performance compromises of using only three active tubes, (c) cheaper, and (d) it is non-directional. Loop type antennas have the disadvantage of being directional, and sometimes you must position the radio for best signal. This might impact how it must sit on a shelf or table. The “Antenna Hank” external antenna eliminates that concern, and works better besides.

typical internal antenna on a radio back

     There were disadvantages. Even with the external “Antenna Hank,” the radio falls a bit short on performance relative to sets with four active tubes. The limited filtering makes for poor ability to separate stations in a crowded metropolitan area, and the relatively poor sensitivity makes it a poor choice for rural use. The large Octal tubes must crowd together closely in a very tight space, making the radio run a bit hot. Tube radios and heat are normal companions, but this little radio pushes the envelope for acceptable thermal behavior. In a few years the miniature tubes that would replace the Octal versions would make for a better heat profile.

     Despite these compromises, this little radio and other similar low cost models opened up the world of radio to many families, and provided many hours of news and entertainment.

     As I examined the little radio, I discovered a couple of bad parts, and a dead tube. It was also very sad looking, cracked and broken power cord, antenna wire missing, paint faded, dial decal all but gone, gold colored grill dented and scratched. The first thing was to repair the radio. I replaced the tube, put a new cord on it, and got it playing. It would only receive one local station. Clearly even though it was not going to deliver outstanding performance, it should be better than this.

     I attempted to align it. The IF can peaked around 600 kHz instead of the 455 kHz it should. It would not realign to the right range, and the frequency coverage was all off, refusing to tune the lower end of the AM band. After trying several times to realign it and failing I started looking for an electronic problem. The B+ voltage on the converter tube was only about 45 volts, when it should be over 100. There was a 2200 ohm 1 watt resistor in that B+ line (R11 in the schematic) that measured over 6 kilohms. I replaced it and the B+ voltage jumped up to about 105 volts and the radio starting behaving better. Now I could align it properly and it covered the whole band quite nicely. Connecting a ten foot hank of wire to the antenna terminal allowed it to bring in all the local stations.

     Now it is time to fix the appearance. First thing I did was to take several close-up photos of the dial, the face and numbers and so on. I then scoured the Internet looking for additional photos of the radio. I then imported the best photo into Photoshop and recreated the dial artwork, matching the original style and lettering as well as possible.

     Next I sanded the radio, and painted it in an antique white finish. I then took the gold painted grill, cleaned it, pushed out the dents and rust spots, and applied new gold model paint to it to refresh its gold hue. Once this was complete, I created a dry-transfer decal from the artwork I recreated, and applied it to the freshly painted case. This was a very frustrating process, but after several failed attempts I attained an acceptable result. I then finished it up with a length of gold cloth-covered cord I had laying about and a new vintage style AC plug.

     This last was a bit controversial. Certainly this cheaply built little radio did not have such an elegant cord and plug. While some vintage radios had cloth cords and plugs of this style, they were rare, reserved for top line, expensive radios.

     I shared the project online on an antique radio forum, and was roundly berated by some who thought I was making a big mistake, that I should put a cheap plastic cord and plug such as was likely on it when new. Nonetheless, I decided I had not set out to restore the radio to “original” condition. I had set out to fix it, and “make it pretty.” I like the elegant cord, and that it is not original does not bother me.

     This is not a rare and expensive collectable radio. It is a relatively common and cheap radio sold by Sears for only one season. Putting a non-original style cord on it does not destroy its value. It really has no value. While I spent some money acquiring it, a few bucks on paint, decal paper and such, and used a number of parts I already had on hand to fix it up, I spent no great amount of money on it. I did spend many, many hours of careful attention. If those hours have any value, this little radio should be worth a couple of grand. If sold today on Ebay I seriously doubt it would bring $100.

     Despite all of this, I have had a lot of fun with the project, and the result is a beautiful, well performing little radio to add to my collection. Value, or lack thereof is not the point.