Before you begin reading this story, I want you to know that what is presented here is more than simply an article, but rather a long story with certain autobiographical elements that I wrote for my own entertainment. I am presenting this story to you free and without commercials in the hope that you will be entertained by it.  Please feel free to scroll down and skip around if you don't wish to read the entire story.  The following several paragraphs are autobiographical, but I do not wish to impose my biography on you if you think it would be very boring, so you may skip ahead to the technology section if you wish to.

     After redrawing the diagram (shown above) I was pleased to note that the radio radio's design is very familiar to me because I could see that it incorporates design features that would be used in almost all radios during the next 25 years.  There were a couple of unusual design features I wasn't immediately familiar with, but they were easy to figure out once I had the schematic redrawn.  Perhaps this isn't necessary, but here's a description of the main design features:

     All the tubes used in this radio had been developed and were made available to the market just a few months before the radio was manufactured and so this radio represented the very latest word in radio design for its time.  These once high-tech tubes allowed for a radio that was simpler and better than radios which were just a year or two older and using less advanced tubes.  I think it is fair to assume that my radio must have been on the drawing board sometime before its tubes were actually available on the market and while they were still in development because there is so little time between when my radio's tubes first came out and when my radio was manufactured.  

     The first detector (or mixer or heterodyne) stage uses a 6A8 tube which is an early type of pentagrid converter tube.  From this time on, most radios will be found using a pentagrid converter tube similar to the 6A8 for its first detector tube.  The 6A8 tube was quite a sensation at the time it came out because it combined two functions in the same tube thus saving a lot of money and making for a simpler and better radio.  Besides doing the mixing, it also functions as the local oscillator (the LO).  The LO signal is created in one part of the tube, but in the same tube, the LO signal is mixed with the weak signal that comes from the antenna.  This off the air or antenna signal has the music and voice we want to hear superimposed on its carrier (called a 'modulated carrier').  So, the tube is both an oscillator and a mixer.  The result of that mixing is the creation of an intermediate frequency (IF) that is used in the next stage.

     A little digression: The circuits associated with this first stage of my radio appeared unusual to me only because the Local Oscillator (or Heterodyne Oscillator) is configured as an Armstrong type oscillator with the +B voltage not applied to the "tickler coil" but through a 10 K resistor after being heavily filtered by a 8 mF capacitor.   I've never seen anybody do that before, but it works.  A local oscillator circuit using pentagrid converter tubes are always configured as Hartley type oscillators not Armstrong oscillators, so this is really unusual.  Now, isn't that just really interesting?  

     As mentioned, the next stage is the intermediate frequency (IF) stage.  The IF stage consists of  filter transformers and the IF amplifier tube (a 6K7).  My radio's IF circuits are completely conventional and functionally identical to all radios that came later.  The 6K7 tube was very special in its time because it is a variable transconductance tube (also called a remote cutoff, or a variable mu tube), as is the 6A8 tube.  Those fancy terms mean that the amplification of one of these tubes can be controlled remotely by applying a negative voltage to the grid of the tube.  As we will see in a minute, the negative voltage comes from the automatic volume control (AVC) circuit.  Having an AVC in conjunction with these special tubes makes it possible to listen to a station who's signal is fading in and out without the volume changing a whole lot.  It also enables you to tune around on the dial without blasting your eardrums if you tune across a loud and strong station.

     The next tube, the 6Q7, is technically known as the "second detector" because it "detects" the voice or music that is on the IF signal.  It also has circuits that generate the AVC mentioned above.   Actually, the 6Q7 is two tubes in one.  The diode section is the second detector and AVC portion of the tube and the other section is a very sensitive audio amplifier that takes the very weak voice and music from the detector stage and boosts it up so that it can be further amplified and be heard in the speaker.  The 6Q7 is another early version of a type of tube that is found in almost all subsequent radios.

     By the way, the diode section of this tube (the "second detector") is actually a Fleming Valve detector circuit that was developed in the early 1900s even before the days of the crystal radio.  The Fleming Valve detector was so good at doing what it did, it was used in all later AM radios until tubes became obsolete.

     As I just mentioned, the diode section of this tube is used to generate the negative automatic volume control (AVC) voltage.  The way this AVC circuit is designed is very familiar to me because this is the famous circuit invented by a young Harold Wheeler in 1925 and patented by the Hazeltine corporation around 1932.  When my radio was made, it wasn't a new circuit, but it was only then becoming popular because of the availability of the new tubes that could work with it.  

     Here's how the Hazeltine AVC circuit works: a Fleming Valve diode AM detector rectifys the carrier to produce a negative voltage in addition to producing voice and music.  Strong AM carrier signals from a strong station will produce a large negative voltage while a weak carrier from a weak station will produce a very small negative voltage.  If this negative voltage is placed on the grid of a variable transconductance tube (like the 6K7), a strong carrier will decrease the audio volume a whole lot while a weak carrier will decrease the audio volume by very little.  This results in the sound level staying close to the same regardless of the strength of the signal.  From about the time this radio was made onward, this simple, but very effective circuit was used in almost all radios.

     I would like to repeat that the triode (right hand) section of the 6Q7 tube takes the very weak music and voice (audio) signal from the Fleming Valve diode detector stage and amplifies it to a usable level so it can be fed to the volume control.  The way the triode is configured in my radio confused me at first because it is biased differently than anything I had ever seen before, but otherwise it is the same circuit that was used in all tube radios that followed my radio.  Although the triode section greatly amplifies the sound, the signal is still not nearly strong enough to drive a speaker and so the audio signal first goes through a volume control and from there it is coupled to a power pentode audio amplifier tube (the 6F6) that raises it up to speaker level.

     The 6F6 audio power amplifier tube is what is called a power pentode.  This tube had been developed so that a single tube could provide enough power to drive a big speaker with plenty of volume.  The earlier radios used lower power tubes and required three tubes arranged in what is known as "push-pull" (technically called "class AB2).  With tubes like the 6F6, radios could be made much simpler, cheaper and better with just one tube in the audio output stage.

     After 1937 the 6F6 would become obsolete as the famous 6L6 family of beam power tetrodes would come on the market and a lower power version, the 6V6, would completely replace the 6F6.  By the way, it is my understanding that the 6L6 is still in production and the last (and most powerful) of this family, the 6KD6 is the tube I use as the power amplifier in my ham radio transmitter.  For simplicity and low cost, radios such as my Fairbanks needs only one 6F6 (or 6V6) tube.  An audio power amplifier that uses a single tube is rarely configured to produce more than 5 watts of audio power, but for really large console radios with more than one large speaker, multiple tubes were configured in the old "push-pull" arrangement (as mentioned earlier) for dozens of watts of power.  Nevertheless, for the smaller parlor radios working into a single high efficiency speaker, 3-5 watts is more than enough to fill a whole room with sound -- and loudly too.  

     Looking back, all these circuits seem very conventional, but at the time this radio was made, it had in it advanced circuits made possible only because of the recent availability of sophisticated, high-tech, high performance, multi-element tubes.  The designer(s) of this radio took advantage of the fact that these new tubes could perform more than one function and they avoided making the radio overly complicated by using no more tubes than actually needed.  At the same time, other manufacturer marketed more "prestigious" and "high-status" radios that had a separate tube for each function.  These much more expensive radios had superfluously high tube counts and were marketed to an upscale customer base at a higher profit margin.  If you can believe it, some of the upscale radios of this era had 15 to 18 tubes, most of which did nothing but cause trouble.  Certainly, many of these upscale radios did sound marginally better and there were customers who demanded the absolute best sounding radio regardless of price.  These were the people who could afford to regularly replace tubes and pay a radio technician to keep their sets working properly.   However, to the ears of most people, these complex radios sounded very little better than the simpler radios.  When you consider that both the simple and the complex radios were used to listen to the less than superlative audio quality that is typical of an AM broadcast, it isn't surprising that most people couldn't hear any real difference between these radios.  Most people considered the simpler radios, such as my Fairbanks, to be an excellent compromise between good sound quality and cost and were therefore the best value for the money.

     Fortunately, for the unknown person who first bought my radio, the designer(s) of my Fairbanks Morse decided to use the latest tube technology and by doing so, they made a simpler radio that not only had excellent performance and was easier to maintain, but it saved that unknown first customer a lot of money and thereby gave that customer a greater value for his/her money.  By designing their radio simpler, cheaper and better than the more expensive radios, they also saved ME a lot of time, effort and expense when I restored my radio.  In short, the designers of my radio back in 1935 were practicing the very best of what today we call modernity.  This radio was a good example of the concept of modernity put into practice.   I think it is very ironic that my simpler Fairbanks Morse radio is today (for me anyway) much more desirable to own than the more upscale radios of the same era.  


     For me, one of the things that is most unusual about this radio is the electromagnet that is used to generate a powerful magnetic field that operates the speaker and doubles as a choke coil to filter the hum out of the power supply.  This was a very old fashioned arrangement and it was used because electrolytic filter capacitor technology had not been well developed and so those capacitors were huge and expensive.  Back in those days, it was cheaper and better to use a big choke coil and to build the choke coil into the speaker where it could be hidden away.  Of course, this would introduce hum into the speaker, but that could be overcome by using another unusual thing I'd never worked with before, a hum bucking coil (the B.C. coil shown in the schematic).  A few years later, new capacitor and tube technology would make it possible to make a similar performing radio with a much simpler, lower voltage power supply.

     Speaking of  power supplys, my radio's power supply is not simple or low voltage.  It produces 250 volts DC using a large power transformer and a full wave rectifier  (the 5Y3 tube).  Using an expensive transformer makes for a safe radio and therefore no back panel was needed to protect people from dangerous and painful electrical shocks.  Later, with the elimination of the transformer and the development of tubes with high voltage filaments, the (in)famous All American Five (AAF) configuration was developed.  These new AAF radios would be smaller, much cheaper to manufacture and much more affordable. However, cheapened up the way the were, they would not have the quality sound of the older radios.  The worst thing about the newer "All American Five" radios was that they were and are much more dangerous than the older radios.  I wonder how many people have been electrocuted by small transformerless radios they foolishly placed in their bathrooms or next to the kitchen sink?

     By the way, 250 volts of direct current (DC) is exposed under the chassis of this radio where only a radio technician can possibly encounter it.  As bad as it seems, this 250 volts is much, much safer than the 120 volts of alternating current (AC) that appears on the very chassis itself of the AAF radios.  Thomas Edison noticed it back in the 1890s that AC voltages are about 10 times more dangerous than DC voltages and so, even if a radio technician should accidentally touch the 250 volts deep inside the underside of the radio, it would be painful, but not very dangerous.  I'm certainly living proof of that because I can't tell you how many times I've been "bitten" by high voltage DC power supplies while working on tube radios.

     Finally, the thing I found very different from anything I had ever worked on before was the way the 6F6 and 6Q7 tubes were biased.  Usually the second detector's triode section is self biased with a high value grid resistor (like ten megohms) and the audio power tube is biased with a resistor and electrolytic capacitor in the cathode circuit.  Well, in those days, electrolytic capacitors were big and expensive (as already noted) and since there was already a large negative voltage available at the choke coil, all they had to do was make up voltage dividers using standard (and cheap) resistors and they would have the voltages necessary to bias the tubes properly.  Because of the way the original schematic was drawn, at first I couldn't quite figure out just what was going on, but after redrawing it, I could see and appreciate the simple, but clever way they biased those tubes.  

   As amazing as this 1930s technology is and how it seems so wonderful to me, the sad truth is that it now so terribly old fashioned and obsolete and I wonder how long it will be before there is nobody left who understands it anymore.  The last of us vacuum tube dinosaurs will soon be extinct and then these old radios will truly be a thing of the past.


     With the end of this technical digression, you might want to read about how I removed parts, put in new parts and got old frozen mechanisms working again.     

     One thing that really threw me was the old fashioned way of assigning values to the resistors.  This set uses very old fashioned resistors (and all of them are still good after all these years).  The colors have faded and the old fashioned color scheme is such that I have found it pretty near impossible to tell what their values are supposed to be.  What I really found confusing was how they were assigned values in the parts list.  Ordinarily, a resistor that has 10,000 ohms of resistance is written as 10K, a resistor that has 1,000,000 ohms of resistance is written as 1M.  In the old parts list of this radio, 10,000 is written as 10M and 1,000,000 is written as 1 megohm which, to me is exactly the same thing.  Since resistors above one or two megohms are very rare (there is only one in this radio), when I saw resistors labeled as 500M and 60M and that just astounded me really threw me into a loop.  Five hundred megohms!?!  Sixty megohms!?! WHAT??  THAT JUST CAN'T BE!!  This had me worried.  I sure hoped that none of the resistors were bad, because in today's world, it would be virtually impossible to find replacement resistors with values like that.  In fact, I have no meters that can measure anywhere near that high so it would be impossible to test them.  

     Before I began working on the radio or even take it out of the wooden cabinet, I began formulating a plan to redesign all the circuits to operate with "normal" values of resistance and replace all the old resistors with their impossibly high resistance.  Thank the gods that it dawned on me that maybe the famous Rider company had made a big mistake and had really meant to write 'K' for 'M.'  In the parts list, when I scratched out  'M' and wrote in 'K', all the circuits started to make sense.  When I opened up the chassis and took direct measurements of the resistors with my ohmmeter, sure enough, they were Kilohm and not Megohms.  What a relief, to know that my radio used ordinary resistors after all.  On doing a little research (thank you Internet) I discovered that in the really old days of radio, M (as in Roman Numerals for 1,000) was used to indicate 1,000.  Who would have thought it, but when you think of it, today we write the year 2011 as MMXI.  We don't write today's year as KKXI, so perhaps I should have known better and not have scared myself as I had.  

     What a lot of time I wasted pondering this foolish little mystery, but I am so glad that I finally figured this out because I was just about to start yanking out and replacing resistors and that would have lead to a real disaster.  I shudder to think how many hours I would have spent  trying to recalculate values for voltage dividers, bias resistors, anode resistors and such things as those.      Well, on the following Monday evening after the radio arrived and after I had obtained a schematic diagram for this radio, I took the chassis and the large, heavy old speaker out of the cabinet.  Once out of the cabinet, I started to pull a pile of horrible looking old parts out of the chassis.  


     On Wednesday afternoon after I had all the electrical, mechanical and cleanup work done,  I plugged in the radio.  As always, I had compared the schematic diagram with every circuit in the radio making double and triple sure that I had everything installed correctly and that everything was as it should be.  I turned on the radio for the first time in maybe 50 years or more with all the confidence that comes with having done all my homework and after a short warm-up, I could hear a normal quiet hiss, but no hum,and nothing smoked.  I then turned the dial to the first AM station that I came to and and a beautiful, mellow sound came out of the speaker - probably for the first time in 50 or more years.  I wasn't expecting all the old tubes to function, but they did, and perfectly.  I then connected the antenna lead to one of my outside antennas and that evening I listened to shortwave broadcasts from all over the world. 

     By the way, it is my firm opinion that this radio was most likely targeted for sale to rural customers and people who were familiar with the Fairbanks Morse name.  Fairbanks Morse was a major supplier of rugged, reliable and affordable agricultural machinery and radios marketed by them would naturally appeal to farming people.  Living in the country, far from broadcast towers, a rural customer needed a radio that could receive broadcasts from long distances and therefore the Fairbanks Morse company did not bother to include a built-in loop antenna, which is useful mostly in urban areas.  To receive both the AM broadcast band and the two short wave bands, this radio has always needed some kind of external antenna and, in fact, farm houses of that era generally had long, high wire antennas just for this reason.  For local AM reception, a short 1 or 2 foot piece of wire is all that is necessary, but for long ranges, a radio of this sort really shines when you connect up a long antenna that is 30 feet or more and the longer and higher you make it, the better.

     To my utter amazement, I found that all the tuned circuits in the RF and IF stages were still in perfect alignment even after 74 years and there was no adjustments I needed to make to improve the radio's already excellent performance.  The dial calibration is right on the money and the tuning is sharp and sensitive with more than enough volume even on the weakest signal.  There is nothing more I need to do with this radio except perhaps to restore the cabinet to look a little newer.  But perhaps I should leave it alone because the first thing that everybody says who have seen my radio say is that it looks like a modern reproduction and not like they would expect an old radio to look.



     I'd like to say something about the fascination people had with listening to shortwave from the period of the early 1930s to about the end of World War Two.  Listening to programs on shortwave from coast to coast, Hawaii and all the foreign countries was all the rage during that time.  These were the days before television, CNN, MSNBC and the Internet so the radio was an important way for people to keep in touch with what was happening in the world and enabled people to find affordable entertainment on a daily basis.   Every country in the world wanted its point of view known and every company wanted its products advertised and there were a lot of listeners out there, so everyone produced entertainment, news and propaganda programs that just filled the airwaves.  Whatever time of the day or night, there was something on the broadcast band and usually some shortwave band was open too.  With so many stations to listen to, a person could stay entertained and informed for just the price of electricity and a new tube now and again.  

     I should mention though that these radios were all hand wired and by today's standards, extremely expensive.  My guess is that a new radio, such as my Fairbanks Morse, sold for the equivalent of maybe $1,000 to $1,500 in the mid 1930s, maybe more.  These were a major purchase (next to a house and car) and so most people had only one (and room for only one) radio back then.  Having a beautiful looking radio (with such a nice dial too!), a radio that sounded so nice and could tune in the whole world, must have been a great source of pride, in addition to its obvious entertainment value.  I can only imagine how excited, pleased and proud the person was when he or she first took this radio to their home and plugged it in for the first time.  I'll bet they invited the whole neighborhood in to listen to it.  

     The voice of President Roosevelt must have sounded many, many times in the very speaker I'm listening to and the electrical undulations of his voice must have modulated the electron stream of many of the very tubes that are still in this radio as he gave his comforting and intimate "Fireside Chats."  I can just imagine the whole family sitting around such a radio at night listening to this or an exciting drama, comedy show or a news broadcast of some important event - like a King's Speech - while during the day the radio would fill the house with the latest big band and jazz music or a baseball game while informing everybody within earshot of the advantages of Palmolive Soap and Wrigley's Gum and how lives are ruined forever by not using Listerine for their bad breath and the efficaciousness of Doctor Vornoff's Monkey Gland Treatment and how if you drink Ovaltine before going to bed, it will help you sleep and you will wake up GAY in the morning and how more doctors smoke Camel cigarettes than any other brand.  

      There are many beautiful old radios that date from this era, but in my opinion, my radio has one of the most beautiful dials of any of those radios.  I think that only the Zenith radios had dials as pretty as mine.  You may have noticed that I'm calling my radio "The King's Speech Radio" because it is altogether possible that the abdication of King Edward ("I can't be King without the support of the woman I love") was listened to, via BBC shortwave, the December following my radio's manufacture and then later little brother Bertie's famous speech was also listened to, again via  BBC shortwave, three years later on September 1939 as Britain began the second great war with Germany.  I think I'm going to add "Fireside Chat" to the name of my radio because it is almost certain it was used to listen to those too.  I love these old radios for their beauty, their interesting technology and the fact that they are an important and key artifact of our culture and civilization from a very important time in the history of the world and my country.  I don't know if my parents and grand parents owned this particular model of radio back in the 1930s, but whatever they owned, it was something very similar.