Albert W. Hull

Albert W. Hull in 1921.

Albert Wallace Hull (born April 19, 1880 in Southington , Connecticut - † January 22, 1966 ) was an American physicist. He is the inventor of the thyratron , the gas-filled rectifier tube, and is considered the inventor of the magnetron .

Albert Hull was born to Francis and Lewis Hull on a farm in Southington, Connecticut , USA . He was the second oldest of nine brothers and had an older sister. Although the family lived in poverty in the countryside, all of the sons in the family received higher education. Besides Albert, Thomas and Daniel also studied medicine and chemistry.

Albert majored in Greek , but received an additional bachelor 's degree in physics from Yale University . In the meantime he taught the Greek language at the Albany Academy, but then returned to Yale University for a PhD in physics. While teaching physics at Worcester Polytechnic for five years, he also did research in the field of photovoltaics .

Research and development work

In 1913 he started work in the General Electric research laboratory in Schenectady (New York) and stayed there until his retirement in 1949. Whitney, its director, had invited him for a summer stay and then offered him a job. In response to Hull's doubts that he probably couldn't do anything practical, Whitney told him that “he needn't worry about the practical part, that is his (Whitney's) business. He should just do whatever he wants. ”This freedom, which Hull later considered to be important for any research in retrospect, made him happy and that was one of the reasons why he stayed with General Electric forever. Even after his retirement, he was in the laboratory almost every day.

Initially, Hull worked with the new vacuum tubes as part of General Electric's efforts to develop novel amplifiers and oscillators. He was also involved in the development of the triode and the patents of Lee de Forest and Edwin Armstrong .

Around 1917, Hull dealt with the previously inadequate possibility of examining the crystal structure of metals using X-ray structural analysis. He independently developed the Debye-Scherrer method , which is called the Debye-Scherrer-Hull technique in the English-speaking world . In addition, he developed the pi filter to smooth the high voltage of his x-ray tube.

In addition to the more well-known projects listed below, Hull worked on: a. also with the following problems:

• Underwater microphones using piezoelectric Seignette salt crystals
• Development of the screen grid tube ( tetrode ) as a result of research on shot noise
• Studies on high-voltage lines along with Stone and - ahead of its time - an experimental high-voltage direct current over 24 km inclusive Thyratrons - Inverter
• Alloys and types of glass for thermally adapted glass / metal connections, as they were necessary for the development of new electron tubes
• Development of a cesium vapor rectifier (the development ended too late and was overtaken by the semiconductor diodes)

Hull's work was reflected in 74 publications and 94 patents.

Dynatron

In 1914, in his first year in the laboratory, Albert Hull invented the Dynatron , a tube with three electrodes: the heated cathode, a perforated anode and an additional plate attached behind it as a second anode. In normal operation, this additional anode has a lower anode voltage than the perforated anode. The secondary electrons released when the fast electrons hit the second anode are absorbed by the perforated anode because of its higher voltage. The characteristic curve of this tube showed a negative resistance and thus this tube could be used as an oscillator and as an amplifier over a wide frequency range for undamping oscillating circuits. With an additional control grid between the cathode and the first anode, a tube called "Pliodynatron" was developed.

Magnetron

As early as 1916, Hull began investigating the influence of magnetic fields on vacuum tubes as an alternative way of controlling the anode current instead of the electric field of a control grid.

Around 1920 his investigations led to the invention of a magnetically controlled switching tube similar to today's magnetrons . This consisted of a cylindrical anode block around the cathode and an external coil for a variable magnetic field axially to the tube. Albert Hull called the amplifier tube the magnetron; he had developed them as an alternative to the grid-controlled tubes to circumvent the patent dispute. Basically he wrote that at the end of the First World War there were electron tubes of small power, but due to the patent situation, no larger tubes needed for transmission systems were manufactured.

Hull's magnetron was tested as an amplifier in radio sets, but was not widely used. It could also be used as a low frequency oscillator. According to reports, in 1925 such a magnetron manufactured by Hull's laboratory was able to generate a power of 15 kW at a frequency of 20 kHz. During this time Albert Hull assumed that his tube would be better used as a high-performance voltage converter instead of in communication technology.

The RF oscillation of the tubes based on the runtime effects of the circulating electrons was discovered - the magnetron was later developed into a microwave generator through the use of resonators with a better understanding of the runtime effects ( Randall 1940) and led to an unprecedented race against time and to a close cooperation between the United States and the United Kingdom in order to use magnetrons to create powerful, short-wave pulse transmitters for radar locating German flying objects. The magnetron was the key to the radar devices initially used by the military.

Gas-filled electron tubes

During the 1920s, Albert Hull took part in the development of gas-filled electron tubes. He discovered how a heated cathode can be protected from the destructive bombardment of ions. This discovery enabled the successful development of the thyratrons (gas-filled triodes ) and the phanotrons (gas-filled diodes ).

honors and awards

Albert Hull was awarded the Morris N. Liebmann Prize in 1930 by the Institute of Radio Engineers (IRE). In 1958 he received the IRE Medal of Honor for “his exceptional scientific commitment and his pioneering work in the field of electron tubes”.

After retiring, he worked as a consultant and served on the Army Ballistic Research Advisory Committee. Shortly before his death, he received the Army Decoration for Distinguished Civilian Service .

Hull became a full member of the National Academy of Sciences in 1929 .

In 1942 he became President of the American Physical Society .

Publications

In 1918 he published an essay on the Dynatron he had invented in the yearbook of the Institute of Radio Engineers (IRE).

Literature and web links

• Literature by and about Albert W. Hull in the WorldCat bibliographic database
• CG Suits, JM Laffert: Albert Wallace Hull 1880-1966 - A Biographical Memoir , published in 1970 by the National Academy of Sciences , Washington

source

• Albert Hull at IEEE history center