TV viewers above a certain age will likely remember Corporal Walter “Radar” O’Reilly of the MASH 4077th frantically spinning the crank on his phone in order to call “Sparky” at HQ and work out some sort of deal to obtain (by questionable, albeit humorous means) some vital medicine or materials (which may also include a better movie for them to watch in the mess hall) For those who have never seen this show, for cry’n out loud go watch it. Now. Come back here afterward. I’ll wait. It is one of the best television programs ever made and even 40 years later (damn, I’m old) the humor and jokes still hold up well. As for his oft repeated frantic phone calls… The phone he was using is the famous EE-8 field telephone.
These sets date back to WWII (slightly before, really) and were used well into the 1950’s and in some cases could be found in military use into the 60’s. Much like the wooden wall phones of the late 1800’s, they are a simple battery powered direct land line connection. The circuit is straightforward, and has provision to support local battery (ie: D cells in the case of each phone) or common battery (powered from switchboard office location) There is an induction coil to improve longer range performance (range is about 17 miles), a ringer bell, and a ringing generator to provide signaling voltage over the line to ring the bell of whomever you are calling. It is this generator that Radar so vigorously cranked to get Sparky’s attention.
The EE-8 was built in three basic versions. The EE-8, the EE-8-A, and the EE-8-B. The basic circuit was also adapted for use in radio patch units such as the RM-29, RM-39, etc. Other versions of the circuit were also used in some amplified sets and the switchboards. But all in all, the telephone end of it worked pretty much the same across the board. Spin the crank, the bell rings…when the recipient picks up, the bell is switched out of the circuit to prevent loading, pressing the butterfly switch on the handset turns on the talk battery circuit and then you can exchange pleasantries and greetings………or call for an artillery strike. (another sort of greeting) When done, you simply release the switch and place the receiver back on the hook switch. Simple.
The three basic versions of the EE-8 are all pretty much the same with only minor changes–with one notable exception: The generator. These generators all do the same thing, by spinning the geared crank, a coil of wire is passed through a magnetic field (or the field revolved within the coil in the case of the A model) in so doing, a current flow is induced in the wire….tapping this off via a basic form of slip ring gives the output power. In these it is about 75-90 volts at about 20 to 30 Hertz. This alternating current is what makes the bell clapper go back and forth hitting the gong…..about 20 to 30 times a second. All of these also have a cam actuated switch that disconnects the phone circuit from the line during cranking so that the high voltage does not harm the talk circuit parts. When you turn the crank, before the gears turn, the shaft slides back a little bit on a cam cut split in it and the subsequent protrusion at the other end operates this switch. In the EE-8 series of equipment, the three variants of the generators are interesting to us geeky types with an historical bent.
The GN-38 generator used in the basic EE-8 model is constructed in a very familiar way– three horseshoe magnets connected to machined pole pieces enclosing the armature. This is pretty much the same as all of those which came before it and commonalities of design can readily be seen in telephones from the 1880’s onward.
The EE-8-A model was initially fitted with a very different generator, although some were also made with the GN-38 and also some used the later B series generator. But the GN-38-A is an oddity here. Instead of the coil being wound upon the armature and spun within the magnetic field, the coils of the A model are stationary and the magnet is within the armature itself. This follows the practice commonly used in aircraft engine magnetos. It works well, and eliminates the slip rings….but in a ringing generator application it is a bit out of place. Perhaps this was an attempt to reduce some manufacturing complexity or to use some readily available materials. During the war such changes, if not technically needed for the device to work properly, would have been driven by material and manufacturing constraints. (the same sort of reasons that resulted in automobile license plates being made of a fiberboard derived from Soy Beans instead of metal like usual.) The GN-38-A is pretty rare. I’ve seen it in the EE-8 manuals, and I have one in my collection, but I have never encountered the A model variant installed in a phone that has come across my bench. It is definitely the rare version. Likely it was only made for a short time before being replaced with the B model.
The EE-8-B (and quite a few EE-8-A’s as well) were fitted with the GN-38-B generator. The B model generator went back to the standard sort of arrangement having the armature coil and stationary magnets. These magnets, however, were an improvement over the horseshoe magnets of the GN-38 and ringing generators of the past. These magnets are compact, rectangular forms that presumably are just as powerful yet they seem to be lighter. In addition to the slight weight savings there is the more important savings in overall parts count as there are just the two magnets instead of three-and their associated mounting hardware. Additionally, by machining the arc shape into the magnet itself, the pole pieces could be eliminated and there was likely a slight increase in magnetic efficiency as well. This variation is by far the most common and is likely to be the only version that anyone will encounter when they find any of these old phones.
And how common do you find these phones? I mean, yeah…sure…Radar had one on TV in the 70’s…but could you have one today? Of course! After the war they hit the surplus market and could be had in Army-Navy stores for just a buck or two a piece. Many ended up in tinkerer’s project bins, others got used as intercoms in houses and factories, mines, kids played with them, some used the generators to go fishing, etc. I had several in my youth and later found a few more here and there. As recently as 10 years ago I obtained four of them at a garage sale. And of course, they can be found on ebay any given day that you choose to look. So yes, pretty common. A collector will be interested in the leather vs canvas case, handset style, etc…..but a very knowledgeable and obsessive collector will be wanting to know which generator is in it. And now you know why.