1922: The Vacuum Tube Amplifier

From a 1922 issue of The American Magazine:



Recently, newspapers all over the world reported that Signor Marconi, the famous wireless expert, had caught certain signals which he thought might have come from Mars. His reason for this assumption was the fact that the length of the electrical waves which carried the signals was considerably in excess of 100,000 meters.

So far as he knew, no wireless station on this globe was using a wave length of more than 23,000 meters. He therefore thought these signals might have come from another planet.

I am not going into that phase of the subject here. But there is another side of it which is of extraordinary interest, because it deals with what is admitted to be the most important electrical development of the twentieth century up to the present time.

Early in 1921, months before Marconi received the mysterious signals I have referred to, a young American inventor, named Earl C. Hanson, told me personally that he had perfected a system which would receive wireless messages having a wave length of 100,000 meters or more! He predicted that the use of this system would absolutely revolutionize wireless practice. He showed me the drawings and specifications for his patents in this and foreign countries. He said that the use of his receiving system would make it perfectly possible to send wireless messages around the globe, without the vexatious interference and delays now encountered.

This achievement will come through the use of what may safely be called the great electrical marvel of the present day — the vacuum-tube amplifier. This amplifier is the essential feature of Hanson’s system. It was because Marconi was using this amplifier that he was able to pick up those signals coming from — he knew not where.

Experts had claimed that a wave length of anything like 100,000 meters could not be used with the old equipment. A low-frequency current is employed to make a wave of that length. A high-frequency current makes a short wave length. This current does not penetrate as well as a low-frequency one. But the latter becomes so feeble, if it travels a long distance, that an ordinary receiving apparatus cannot pick it up. The vacuum tube amplifier disposes of this difficulty and will make it possible to talk around the globe, easily and quickly.

The story of this tube is a romance of science. Before many years you will become as familiar with the new electrical miracle as you are to-day with the incandescent light and the telephone. You ought to get acquainted with it now. So here are a few chapters from its story:

Lying on my desk at this moment is a glass tube, a little more than half an inch in diameter and about an inch and a half in length. I have spent days in getting acquainted with this contrivance and have come to regard it with something approaching awe.

I was introduced to it by Mr. Hanson, the young inventor I have just mentioned. Mr. Hanson can hardly remember a time when he was not experimenting with things electrical. He confesses that as a seven-year-old boy in California he used to go down to the cellar and deliberately pour the solution out of the batteries connected with the front doorbell. He knew that if the bell was out of order, an electrician would be summoned. Then he would get a chance to ask questions.

As he grew older he concentrated his interest on the problem of the wireless telephone; and when he was barely in his teens, he did succeed in talking, without wires, over a short distance. Year in and year out, he continued to work on the idea of wireless transmission in different forms. But it was not until this little tube was available, that he and other inventors who were struggling with those problems were able to give us some of the greatest marvels of the age.

I first saw the tube in Alexander Graham Bell’s former laboratory in Washington, where, through the courtesy of Doctor Bell, Mr. Hanson had been conducting his experiments. He took a small object from his pocket and asked me to look it over.

“It doesn’t seem much more impressive than a child’s toy, does it?” he said. “But probably a million dollars have been spent on it; and already several hundred patents have been taken out to cover different phases of its progress.”

After an introduction of that kind I naturally examined the object with a good deal of curiosity. It was simply a glass tube, closed at one end with a point, like an electric light bulb, and sealed at the other end into a black base. Inside of the tube I saw a fine wire filament, a wire spiral around it, and, outside the spiral, a very thin piece of metal curved into a cylinder, open at one side. I was asked to believe that this little device was one of the marvels of the age.

“What will it do?” I asked.

“Do!” exclaimed Mr.Hanson. “If I told you all the things I expect it to accomplish, or to help to accomplish, you wouldn’t believe me; but I’ll tell you some of them, at any rate.

“It will help the deaf to hear; it will make your voice audible across the continent — even around the globe; it will enable vessels to find their way through fog and darkness; it will save the lives of people in aeroplanes; it will make wireless telegraphy far more efficient; it will help to win wars; it will enable one person to talk directly to thousands, in an ordinary tone of voice — just as it enabled President Harding to talk to one hundred thousand people at his inauguration, and on Armistice Day.

“We call it a vacuum tube. The fine tungsten wire in the center is the filament; the spiral wire around it is called the grid; and the little metal cylinder is the plate. Years ago Mr. Edison made a vacuum tube containing the filament and the plate; they formed the two electrodes. He never made extensive commercial use of it and, in due course of time, his patent expired.

“Some years afterward, Professor Fleming, Marconi’s chief engineer, used the tube as a detector of wireless waves or vibrations. Then, a few years later, De Forest added a third electrode, the grid. And the addition of that one thing, just that little wire spiral, has made it possible to accomplish things on which inventors had been working unsuccessfully for years.

“You have heard of electrons — those invisibly minute particles which many scientists consider the final unit into which all matter can be divided. Well, when an electric current was sent through the Edison tube there was a constant stream of those electrons passing from the filament to the plate. But when the grid was introduced it had the effect of amplifying the energy received.

“Here is one way of illustrating it: Suppose a great steam pressure has been generated with a force of many pounds to the square inch. One man, even a very frail one, could control that great force simply by turning a lever that would open or close certain valves.

“Now, if you will imagine an electrical current, instead of steam, and think of the grid as the man controlling it, you will have a fairly good idea of how it works. The point is that we can take a feeble energy, coming in by one wire, and by means of the grid add a lot more energy from another source, and vastly increase the feeble current.

“Let me show you one way in which this has been applied. Here is an apparatus for the use of the deaf. I call it a vactuphone, which is a contraction of ‘vacuum-tube-phone’.”

Mr. Hanson showed me a leather-covered case which looked like a small camera box. In one side of it was a two-inch circular opening covered with a wire screen. On the other side was a small arm, or switch, which could be moved in a circle. Mr. Hanson took from a small compartment in one end of the box a flat telephone receiver, connected with parts of the inner mechanism. He told me to hold the receiver to one ear. He then walked to the opposite end of the long room and began to speak. Instantly I took the receiver from my ear.

“Don’t shout so loud!” I exclaimed. “It’s terrific.”

He laughed and said quietly, “I wasn’t shouting. I was speaking as low as I am now. Turn the switch at the side until you get the sound as you want it. I’ll go farther off, too.”

He went out, crossed a hall, and walked to the end of the opposite room, about forty feet from where I was standing. There he began speaking again. Without the aid of the instrument I could barely hear his voice. I could not distinguish that he was using words at all. But with the receiver at my ear, he still seemed to be shouting at the top of his lungs. The transmitter — which is back of the screened opening in the box — was not even turned toward him at the time.

He made other tests which were astonishing: going into a corner of the room, for instance, and speaking in a low tone with his back toward me. Even then he seemed to be shouting into my ear.

“Of course,” he said, coming back to the table, “you don’t need to have sounds amplified that way. A deaf person could not hear at these distances, even with the aid of the instrument. But his hearing power and range would be greatly increased.

“The diaphragm in an ordinary telephone is very sensitive to sound vibrations. That is the reason why some deaf people can hear over the telephone much better than they can hear a person speaking directly to them. The current which comes over a telephone wire is a low-frequency current. It is also called an ‘audio-frequency’ current, because it produces vibrations which we can hear without their first being changed in some way. But these vibrations are not powerful enough for the ear of a deaf person.

“When powerful vibrations are employed, you get a great volume of sound, but it is so full of squealing and hissing and sputtering noises as to be unintelligible. But the little grid in the tube, controls the energy coming to it, so that you get a smooth reproduction of the natural vibrations made by the voice in speaking. You get clarity as well as volume. Used in ways like this, we call it the vacuum tube amplifier.

“President Harding’s voice was amplified more than a million times by the apparatus used when he delivered his inaugural address. I believe that he could have been heard half a mile away; yet he was speaking in moderate tones. The telephone company spent many thousands of dollars, just to give that demonstration.

“No instruments of any kind were visible to the throng that listened to Mr. Harding. Underneath the platform from which he spoke were three rooms containing a powerful electrical installation, which included several sets of vacuum tube amplifiers.

“You see, we do not have to stop with one tube. We can pass the current on, from one to another and another, constantly getting, and controlling, greater and greater power.

“Just see what this means: It is estimated that one unit of electrical energy is increased ten times by means of the vacuum tube amplifier. Start with one unit and multiply it six times successfully and you get one million! That means that if you started with one unit of electrical energy and passed it successively through six of these tubes you would have amplified it a million times.

“Can you imagine the possibilities involved in that statement? If I had a tuning fork here I would show you something interesting. You know that if you make the prongs of a tuning fork vibrate rapidly you get a musical note. I could make them vibrate so gently that they would give out no sound audible to the unaided human ear. Yet, if I should hold an almost imperceptibly vibrating tuning fork close to the transmitter of the vactuphone, you would hear its musical note.

“In this way we shall be able to listen to sounds which no human ears have heard since the world began! It may be that we shall actually be able to hear things growing, and to listen to the changes that are taking place in matter.

“Last winter, The American Magazine caused a sensation when it published an interview with Edison, in which the scientist said he was experimenting with an instrument which should be able — if anything known to man could do it — to receive some sort of communication from the spirit world, if there is such a world.

“Mr. Edison never has revealed to the public what kind of an instrument he is experimenting with. I do not pretend to know what it is. I have not heard of anyone who does. But I have heard scientists, speculating on the matter, declare that, whatever the instrument may be, it probably used the vacuum tube amplifier in some way. This seems plausible; for the tube can catch the feeblest impulse of energy and magnify it almost incredibly.

“Some months ago, I read an interview with Charles Steinmetz, the great electrician. It was evidently suggested by the Edison interview, for the reporter was asking Steinmetz what kind of an electrical instrument would come nearest to making ‘spirit communication’ possible.

“Mr. Steinmetz did not think we could get such communication by any physical means, because the spirit itself is not physical. But he said that the nearest approach to it came from an instrument which wrote messages that came on wireless waves through two thousand miles of space. These waves were caught by antenna;, passed through six vacuum tubes, one after the other, which magnified a million times the electrical energy received. You see, again the miracle worker was our friend here, the vacuum tube amplifier.

“But we don’t have to speculate about what may happen in the future because of this marvelous invention. Let me tell you some of the achievements already to its credit:

“Did you know that we were not able to telephone across the continent until the vacuum tube amplifier made it possible? An audio-frequency current — a current producing a sound audible to the human ear — if sent over three thousand miles of wire becomes so feeble, before it reaches that distance, that the telephone receiver is not able to pass it on to the human ear. But by using the amplifier we can talk over a telephone wire from New York to San Francisco. This was first done publicly in January, 1915, and was considered one of the marvels of the twentieth century. But greater wonders were soon to come.

“Do you remember how, in October, 1915, the government wireless station at Arlington, near Washington, talked with a wireless station on the Eiffel Tower in Pans, and the messages were heard also at a station in Honolulu? This was made possible by the special equipment installed by the American Telephone and Telegraph Company and the Western Electric — and the vital feature of that equipment was the vacuum tube amplifier.

“The ones used in that case were considerably larger than this one, and there were rows and rows of them — six hundred altogether. As someone has said, they were veritable ‘talking bottles.’

“The American Magazine had an article, some months ago, about the mammoth new station of the Radio Corporation on Long Island, which will make it possible to telephone around the world. The vacuum tube amplifier was the principal factor in this achievement. And the developments which are going on, in regard to it, will add other marvels to those already accomplished.

“One of the results of the development of the vacuum tube is that ships are now able to find their way by means of the radio-compass, in connection with which a vacuum tube amplifier is used. This method is of real service in bringing a vessel to port.

“But it did not solve another problem which is often a very serious one, that of bringing a vessel into a harbor. In case of the heavy fogs which are common at many ports, ships are often compelled to anchor outside the harbor and to wait, sometimes for hours at a time, until the fog lifts. The annual loss from this cause is estimated to be millions of dollars. When a great passenger liner is held up, sometimes for ten or twelve hours, the loss to the company alone is heavy, for the cost of keeping such a vessel at sea with its passengers is sometimes as high as five hundred dollars an hour. All this time, moreover, the dock is tied up and dozens of workers are kept idle.

“Not only this, but hundreds of vessels are lost every year, by collision with other vessels, or by getting out of the channel and running on rocks, when trying to enter or to leave harbor in a fog.

“It was to overcome this great loss that I invented a system of piloting ships into port with safety even during the densest fog. And again it was the vacuum tube amplifier which made this possible.

“Briefly, and without technicalities, this is how it is done: An insulated cable is laid along the bed of the channel. This cable is connected with an electrical installation on shore. What we call a magnetic field is produced; that is, magnetic waves emanate from the cable. A ship is equipped with coils of wires, one at each side toward the bow of the vessel. These coils pick up the magnetic energy, which is then passed through a vacuum tube amplifier and produces a musical hum in the telephone receiver worn by the navigating officer on the bridge.

“The officer, by simply moving a switch, can listen first at one side of the ship, then at the other. If the port-side signal is louder, he knows he is to starboard of the cable; and the reverse if the starboard signal is the stronger. Going in either direction, he always keeps to the right — to starboard. So two vessels can go ahead safely in opposite directions, even though the fog is so thick that they are invisible to each other, simply by ‘listening to the cable.”

“In October, 1920, demonstrations of the system — which I call the Audio-Piloting System — were given in New York Harbor with the cooperation of the United States Navy Department. The vessel used was a destroyer, the ‘Semmes;’ and in order to show how the system would make a pilot absolutely independent of the necessity of seeing his course, the bridge was enclosed in canvas. If the steering apparatus, and the man guiding the vessel, had been in the very heart of the ship, it would have been just as easy to guide it safely into the harbor.

“Various persons did pilot it, simply by ‘listening to the cable.’ Captain Battle, for instance, of the Cunard Company, without any previous experience with the system, was able, after a little coaching, to bring the ‘Semmes’ into port, keeping the vessel within fifty yards of the cable all the way and always on the correct side of the channel. Yet he could not see anything outside of the canvas walls shutting in the bridge.

“The Government is now using this audio-piloting system on some of its war ships, and has agreed to loan several , of the installations to merchant vessels.

“That is one thing we can do, thanks to the vacuum tube amplifier. We shall be able to use the same system in guiding aircraft to a landing. By surrounding a landing field with wire, in much the same way as we mark the channel with a cable, and by equipping an aeroplane with coils and a receiving apparatus, the aviator not only can tell when he is near a landing field, but can also guide his machine so that it will come down in any part of the field that he chooses for his landing. And he can do this in fog, which is the aviator’s worst enemy.

“Aeroplanes can use the audio-piloting system just as vessels do. A telephone wire, from one aerodrome to another, would take the place of the cable laid along the channel to a harbor. And the aviator, by listening through his receiving apparatus, could follow this wire. This, in fact, has been done; and it will very greatly diminish the danger of night flying. Aeroplanes have even followed a submerged cable, just as the ships do.

“During the war the Allies used the audio piloting system at various ports and also to guide vessels through the mine fields. And don’t forget that the vacuum tube amplifier was what made this possible. The Allies and the United States used the audio frequency apparatus for tapping the German telephone and telegraph lines. With its assistance they could listen in and hear what the Germans were saying over their telephone wires paralleling the trenches.

“This audio frequency system was one of my inventions I called it ground telegraphy The French translated that into telegraphie par sol and the system became generally known as ‘T.P.S. It is a wireless circuit in which the vacuum tube amplifier plays the star role I perfected it in January 1911 but experts laughed at it then. Later I applied for patents. But at the request of the Government the patent was held up during the war. It has now been issued both in the United States and most of the foreign countries.

“We are constantly discovering new ways in which the vacuum tube can be applied. For instance the Edison tube — which is the one with only two electrodes — is now used in a device for charging storage batteries. It can be installed in any garage to charge the batteries in an electric automobile and it does the work in a third of the time that has been necessary. The vacuum tube is used also in X-ray work making some very decided improvements. And I have patented apparatus which makes it possible for patients in all the wards of a hospital or other buildings to hear music or speaking in another room or another building.

“A few months ago Wendell L. Carlson and I, working together, found another use for the vacuum tube. You know that there are various electrical devices used for therapeutic work. And you also know that the patient has to put up with unpleasant twitchings and jerkings when being treated with some of these appliances. We found that by using a vacuum tube circuit these spasmodic jerkings could be completely eliminated.

“The tube is employed in detecting changes of temperature. It can be used in locating oil and also ore bodies; for it is so sensitive that the most feeble magnetic energy can be picked up and amplified. In fact, there seems to be no end to the possible uses of this wonderful little thing.

“Not that it is always little. On the contrary in some of the recent developments the ‘tubes’ are very large. The glass container is dispensed with and the metal ‘plate,’ which you see inside this little tube here, becomes its own container. These metal plates become so heated by the bombardment of the stream of electrons that experiments are now being carried on to water-cool them. The ‘plate’ will be made of hollow tubing through which the water will circulate.

“I called the vacuum tube the most important electrical development of the twentieth century. So far It seems to me that it will hold that position for a long time to come.”

Original page image (final image three partial pages combined into one), click to enlarge:





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One response to “1922: The Vacuum Tube Amplifier

  1. Handel Audio

    Reblogged this on handelaudioblog.

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