Auszüge aus The national in the world war 1917-1918 Seite 229-246 Vacuum Tubes The Adaptability of the National Lamp Works to Vacuum Tube Manufacture No other part of the war work performed by the National I.amp Works was so nearly like its own particular line as that done in connection with the development and manufacture of ''vacuum'' tubes and ''`X_Ray'' tubes. ln fact, from the standpoint of general construction, these tubes were nothing more nor less than very expensive and highly complicated lamps. To be sure, their purpose was not to give light, but, like lamps, they were made up of glass bulbs containing filaments and had to have the air pumped out of them in a skillful and highly specialized way. It is not at all surprising, therefore, that the Lamp Faciities I.ahora- tory at Nela Park was conspicuously successful in this par- ticular branch of the war work of the National. Since the vacuum tubes were used principally in wireless telegraphy and wireless telephony, both on the battlefields and in all the work back of the lines requiring a rapid and dependable system of communication, and since all this work came under the direct supervision of the Signal Corps of the U. S. Army, a few explanatory remarks regarding the latter Corps will be in order here. HOW THE PLIOTRON AND KENOTRON TUBES OPERATE The vacuum tube, commonly called the pliotron, and mentioned so often in this story, deserves many chapters to cover the fascinating story of its developnient; particularly the wonderful scientific laws which govern its action and the almost unbelievable amount of work that was accomplished by the Company in supplying the needs of the army and navy with these tubes. The amount of progress that the world owes to these tubes is a source of just pride to all those engaged in the work at the laboratories and lamp factories where so much of the work was done that led to their highly developed state. To give the reader a better idea of what the vacuum tube is used for, and to state briefly the principle of operation of the tube, it is well to review the developments leading up to the rather unsatisfactory use of the tube at the outbreak of the war early ln I917. The vacuum tube had its beginning in tlie ''Fleming valve,'' named after Dr.Fleming of England, who discovered the peculiar action now known as the electron emission phe- nomenon; that is, if a cold material he placed close to a heated metallic substance or filament, there is a flow of negative elec- trons from the filament to the colder material. This phenom- enon is utilized in the vacuum tube by employing a cold plate, usually of nickel or molybdenum, which is called the "anode,'' and a hot tungsten filament or "cathode.'' When this filament is heäted in a highly evacuated space,it gives of '"electrons''- negative charges of electrical energy. The electrons flow from the hot cathode to the cold anode and, by using the proper instruments, can be measured. The flow is controlled by the temperature of the filament; the higher the temperature, the greater the flow of electrons. This particular type of tube hav- ing the two elements, i.e., the plate and the filament, was named the "kenotron'' tube (''keno,'' a Greek root, signifying "ernpty'' or "a vacuum''). A "WIRELESS'' DETECTOR This discovery was further improved by Mr. De Forrest, who inserted a third member between the filament and plate, called the grid. It was found that by varying the voltage on the grid it was possible to control the flow of electrons from the cathode to the anode. The peculiar feature of the grid control was that very small changes in grid potential produced very large changes in electron flow. This feature made the tube suitable as a detector and reproducer of very weak wire- less signals. It changed, or "mplified,'' wireless signals of radio frequency into signals of audible frequency. This three- element type of tube having a filament, plate, and grid, was known as the "pliotron'' ("plio,'' a Greek root, meaning ''am- plify''). Hence, pliotron conveys the idea of an instrument capable of amplifying, --that is, of making feeble signals stronger. Shortly before the entrance of the United States into the war, Dr. Irving Langmuir of thc General Electric Company's Research Laboratory at Schenectadv, New York, produced vacuum tubes of this three-eleinent type which proved to be the most satisfactory of all the types then in use. In July, 1917, when the Signal Corps and the Navy became particularly interested in wireless communication, it was found that these tubes were being reproduced only in laboratories, and involved very elaborate laboratory processes which did not permit of commercial manufacture. WONDERFUL IMPROVEMENTS MADE IN THE TUBES During the commercial production of receiving tubes, hardly a week went by without improvements either in the quality of the product or in the facilities for manufacture. The method of exhaust had proven unsatisfactory from the very first. Not only was the process long and tedious, but the vacuum finally obtained was not suffciently low to insure perfect operation of the tubes. All sorts of experiments were tried, including the use of chemicals, in the endeavor to find a better method. Palladium black was introduced in the top of the tube as an absorbent for the gases given off by the metal parts. A little later, a form of charcoal, very similar to that used as canister-filter for gas masks, was tested and proved quite successful. Early in May, I918, an exhausting procedure was evolved which was revolutionary both in the speed with which the tubes could be exhausted and in the completeness of the exhaust. A chemical, similar to the so-called "getter'' used in exhausting MAZDA B lamps, was introduced in the top of the bulb. The use of this chemical in connection with the "Bombardment Process'' of exhaust previously mentioned, proved to be by far the most satisfactory of all the exhausting methods then in use. Enough of the chemical was used to take care of the small amount of gas constantly emitted by the metal parts during the actual operation of the tube. When the first pliotron manufactured was rated on a "Cable Box,'' an arbitrary method of comparing quality, it gave an amplification rating of 8 miles. Within a month this rating was raised to an average of 12 miles, and before 10,000 tubes were made the average was 16. By the time 25,ooo tubes had been manufactured, this average rating was over 20 miles. The direct measure of quality varies as the square of' these ratings or in the ratio of 64 for the first tubes, to 400 for the last tubes on order. This meant an increase in quality of over six times! The life of the tube was also increased (from 3oo hours to 2,ooo hours) and, as a result, the tubes gave the Government seven times the life expected. In addition to this wonderful improvements were made in uniformity of the product. All this progress, however, was not made without diffi- culty. On one occasion, out of nearly 2,000 tubes that had been made up, not a single one was good for anything. Several times the Division was confronted with losses of thousands of dollars, due to imperfect raw materials and uncontrollable circumstances. All of these problems kept every man working night and day, and required the best possible supervision and engineering. One of the greatest handicaps under which the Division was working during these months, was the limited production schedule imposed by the Government. Continued requests were made for release from this restriction, in order to make it possible to obtain more efficient operation by means of a greatly increased rate of production. Finally, the superior quality and operating characteristics of the tubes excited the interest of the allied governments; the G. E. Research Laboratory received a request from the British Admiralty for tubes, and immediately asked for increased production. This time the Vacuum Tube Division promised to reach a production of3,ooo tubes per day within sixty days, and began to make plans to produce this number of tubes. The order failed to materialize, however, but with permission from the Signal Corps a maximum production of 1,8oo tubes per day was obtained. As a result, the Division would have been able to carry out its promises quite easily. Having completed the receiving tube order ahead of schedule, however, the Division ran out of orders and was forced to ask for more orders to keep the plant in operation. It became evident that the Vacuum Tube Division was so far ahead of the Government program that it was necessary to cut production, as more pliotrons were being made than the Government could handle. The Division was complimented for its proven ability to deliver tubes ~ large quantity and, while so doing, to make wonderful improvements in the quality of the tubes. Generally speaking, the production of pliotroii trans- mitting tubes and of kenotron regulator tubes was a repe- tition of the receiviiig tiibe experience. The Division im- proved quality, made deliveries on or ahead of schedule, and was aIways ready in an emergency to take up new devel- opments or to make new types of tubes. A medium-power transmitting tube was finally devel- oped for the Navy, close co-operation with the G. E. Research Laboratory being maintained throughout the entire develop- inent period. This development, while not complete, was probably the most wonderful of all from a technical standpoint, due both to the equipment developments involved to produce the parts, and to the careful work required to produce these tubes successfully. Special tubes of various types, and innu- merable parts, stems, mounts, etc., were produced at Nela for experimental use by the G. E. Research Laboratory at Schenectady. The following is a list of the total number of tubes manu- factured and shipped from Nela Park. Receiving Tubes 77,290 Transmitting Tubes 36,649 Regiilator Tubes 49,575 Resistance Tubes 5,998 Special and Misc. 9,803 TOTAL 179,315 lt is of interest to note here that the Vacuum Tube Division of thc National Lamp Works manufactured and delivered three times as many tubes as any other organization engaged in the same class of work. The question of the price of the tubes was handled at Schenectady and contracts were made on a definite price basis, the price being determined from the actual cost figures of manufacture of the pliotroiis submitted to the Government. While the price received for the tubes did not result in any big profit, it was sufficient to cover any reasonabIe cost. Of course, no return was received on the fund of information and experience collected from years of lamp-making devel- opment, which was responsible for the success of the Division in the commercial manufacture of pliotrons. Knowledge of tungsten filament wire, glass, platinum substitute, pumps and a]l manufacturing equipment is very properly considered as being one of the important intangible contributions of the National Lamp Works towards the winning of the war. USES OF THE VARIOUS TUBES MANUFACTURED The particular uses to which these pliotron and kenotron tubes were adapted by the Government are as follows: First, as detectors and amplifiers in the reception of wireless telegraph and telephone signals; second, as oscillators and modulators in the transmission of wireless telephony; and third, as regulating devices for variable-speed generators mounted on airplanes for supplying high voltage to the trans- mitting tubes. The detailed theory of operation of the receiving tube is highly tech- nical and is therefore omitted from these pages. It is sufficient to say that the vacnum tube (pliotron) is, by far, the most satisfactory type of detector for wireless signals so far developed. The simplicity of the receiving circuit, together with the fact that it is always constant and never out of adjustment, makes the vacuum tube the most re|iab]e feature of the wireless receiving equipment. The first receiving tube made by the Vacuum Tube Division was merely a laboratory sample, designated as the G-20. The making of this one tube furnished a fund of information and experience which later proved quite invaluable, and from which the commercial developments on receiving tubes started. The principles of construction used in this first experimental tube were incorporated in the receiving tube, Type CG-886, which was the first commercial type manufactured. This tube was supplied to the U. S. Navy to be used as a detector, amplifier and oscillator, both aboard ship and in land stations, and was usually operated in series with a resistance on a three-cell storage battery. The construction of this tube embodies a tungsten filament, a tungsten grid and a nickel plate, all elements being cylindrical in form. The base used for this tube was the old type of 3-pin navy fibre base, which was later superseded by a 4-pin standard base used by both the Navy and the Signal Corps of the U. S. Army. A little later, the Type VT-11 tube was developed for use by the Signal Corps of the U. S. Army as a detector, amplifier and oscillator for both field and air service. The tube is operated directly across a two-cell lead storage-battery without any resistance in senes. The construction of this tube embodies a tungsten filament, a tungsten grid and a nickel plate, all elements also being cylindrical in form. The base used on this tube was the base standardized for receiving tubes by both the U. S. Army and Navy. Another tube, which was in the development stage at the time the armistice was signed, was the Type VT-13. This is a modification of the VT-11 tube, the endeavor being to improve both the ruggedness of the tube for airplane service and its radio characteristics. The service of this tube was identical with the VT-11. AMPLIFIER TUBES When wireless messages are too weak to be heard in the telephones of the detector circuit in the receiving station, a second vacuum tube is inserted which amplifies the signals and increases their audibility. This second tube is called an amplifier and, in many cases, the signal is ioo times greater in audibility due to the use of the amplifier. Such an amplifier tube, known as Type CA, was developed for use by the Navy in connection with high-speed photographic receiving apparatus. It was a special tube developed to obtain the maximum amp]ification and embodied a tungsten filament with a finely wound tungsten grid and a tungsten plate. TYPE OF TRANSMITTING TUBES The second use of the tubes, as transmitters, was not completely developed before the armistice was signed, but a large number of tubes were constructed and used on submarine chasers, airplanes and flying boats for wireless telephony communication up to about 12 miles. Inasmuch as the transmission of wireless signals for any distance involves considerable power, the tubes used in transmitting stations had to be of a heavier and more rugged type of construction than the receiving tubes. The first transmitting tube produced was a laboratory sample, from which the full|ine of tungsten-filament transmitting tubes was developed. The transmitting tube ''Type VT-12'' was the first commercial develop- ment, and was used by the Signal Corps of the U. S. Army for wire|ess telephony in airplane service. This tube was an endeavor to duplicate the electrical specifications of the VT-2 developed by the Western Electric Company. It embodied a tungsten filament,a tungsten grid and a molyb- denum plate, all elements being cylindrical in form. The limit to the amount of power which could be supplied to the tungsten filament limited the range of wireless telephony transmission, with the sets originally developed for Western Electric tubes, to about three miles. This tube was finally super- seded by the VT-14. The transmitting tube "Type VT-14,''was developed to give the same transmitting range, in sets developed by the Western Electric for the Signal Corps, as was given by the VT-2. The construction and detai|s of the VT-14 are exactly similar to those of the VT-12, with the exception of a greater power input to the filament. This tube, when used on airplane service, had a transmitting range of from 10 to 15 miles in wireless te- lephony. The VT-14 was also adopted by the U. S. Navy, and called by them the CG-1162. It was used on submarine chasers and flying boats, with a sending range of about 15 miles. Another type of tube, Type VT-I6, was in the development stage for theSignal Corps of the U. S. Army at the end of the war, and was constructed with the endeavor to improve the mechanical strength of the tube for air- plane service and to perfect its electrical and radio characteristics. PRESIDENT WILSON TALKS 600 MILES THROUGH A VACUUM TUBE At the beginning of the development of transmitting tubes, two miles was considered a most excellent showing for wireless transmission of speech, in view of the dificulties encountered on airplanes, flying boats and submarine chasers. The rapid progress which was made in the development of these tubes led to further developments, and shortly after the armistice was signed a flying boat established commu- nication off Norfolk at a distance of about 80 miles. A little later, the Vacuum Tube Division, co-operating with the Re- search Laboratory at Schenectady, developed a medium power transmitting tube for wireless telephony, known as Type CG-1144. This tube was used by the Navy on flying boats and aboard ship, for transmission of wireless telegraphy and telephony. It embodied a tungsten filament, a tungsten grid, and a molybdenum plate, and was designed to use a higher plate voltage than the VT-12, VT-14 or VT-16. This tube had a transmitting range of from about 50 to 175 miles, a flying boat establishing communication with Secretary Daniels in Washington at a distance of 150 miles at sea. The range. could be increased by using several of the tubes in parallel, successful communication being established be- tween President Wilson and Secretary Daniels when the "George Washington'' was 600 miles out of New York. From the time when this conversation started wireless telephone communication was successfully maintained until the ship reached harbor. FIRST AIRMEN TO FLY ACROSS ATLANTIC USED VACUUM TUBES While lying in harbor at Brest, France, awaiting the arrival of President Wilson for his trip home, the George Washington maintained successful communication with the famous trans- Atlantic plane NC-4, which was then passing over Brest en route from Lisbon, Portugal, to England. The George Wash- ington talked to the NC-4 by radio phones,and the crew of the NC-4, telegraphing their replies back to the George Washington, stated that the phone signals were coming in "]oud enough to hurt their ears.'' Both the radio telephony and telegraphy transmitting sets were using CG-1144 vacuum tubes. Coinmunication was maintained until the plane was well over so miles away. The perfect reception on board the George Washington of the signals from the NC-4 was con- sidered even more remarkable when it was learned that the plane, on account of heavy fog forcing it to fly low, was not using its main antenna. The Iatest type of tube which was developed by the Vacuum Tube Division was successfiil]y used for wire]ess telephone communication between Brunswick, New Jersey, and Brest, France. This medium power tube was developed to withstand the necessary mechanical strains in connection with airplane service and to give the most reliable service in all of its electrical and radio characteristics. With regard to the transmitting tube, the Vacuum Tube Division of the National Lamp Works were the only successful manufacturers of this type of tube. The tubes was used almost exclusively by the Navy in their equipment for sub- marine chasers and flying boats, and were pronounced as being singularly free from operating troubles and as giving the most satisfactory results. This development was beyond the fondest hopes of the engineers connected with radio devel- opment, especially wireless telephony. REGULATOR TUBES (KENOTRONS) The regulator tube ''Type TB-1'' was used in regulating the voltage across the terminals of a fan-propelled generator for airplanes. This is a two.element tube or kenotron, embodylng a tungsten filament and molyb- denum plate, and was so connected into the field and armature windings of the generator that with airplane speeds varying from 4o to 180 mi|es per hour, corresponding to armature speeds of 3,500 to 18,000 revolutions per minute, the voltage did not vary more than 10 per cent. The construc- tion of this tube was such that it withstood mechanical vibrations in air- planes without any effect upon its electrical behavior. The use of these tubes with the generator equipment very materia||y decreased the amount of weight required to provide the necesmry voltage for wireless communication. They were used exclusively on Amencan planes, and, from all reports, were entirely successful. ln all of the developments of the tubes used on airplanes, it was nec- essary to cover the construction specifications most thoroughly, so that the tubes would meet the service required. The vibrations of the plane and the sudden shocks and jars of landing necessitated the most accurate and rigid designs on all types of tubes. By means of the most elaborate internal construction we met all requirements of the service. The wonderful part of all of the development activities was the speed with which most successful designs were placed in production and delivered to the Govern- ment, and the surprising uniformity and improved quality which resulted from concentrated effort on commercial production. Articles published in the various technical magazines by members of the Signal Corps and by those connected with this radio development, speak very highly of the progress that was made in wireless telephony during the war, and a major part of the credit is due to the development of the vacuum tube, without which it would have been entirely impractical to have attempted wireless telephony in the air service. THE GRID LEAK AND SPECIAL TUBES The grid leak tube, a small cylindrical vacuum tube, was developed as a necessary auxiliary tube to be used in connection with the larger trans- mitting and receiving vacuum tubes in wireless telephony outfits, as a leak around the blocking condenser used in the grid circuit. Grid leaks were made having a resistance of 500,000, 2,000,000, and 10,000,000 ohms. The resistance is formed by deposits of metallic tungsten in a film between the two terminals of the grid leak. . A special relay tube was also developed for John Hays Hammond, Jr. This was a specially designed tube used as a relay in connection with the wireless control of torpedoes.