Arjun Duggaraju
Yonathan Ayalew
English 2116-007
May 2, 2011
The Vacuum Tube
What is a Vacuum tube? It is a glass tube with a vacuum inside which allows
electric currents to pass freely within the vacuum from a positive electrode to a negative
electrode. In between the two electrodes would be a thin filament which emit’s electrons
which in turn makes electrical energy. The vacuum tube is used in various applications
such as: Amplification, Rectification of AC (alternation current) to DC (direct current),
Radio and radar frequency oscillation, etc. The invention of the vacuum tubes sparked the
electronic revolution in the 20th century. This invention also fueled the invention many
other sources of energy in the electrical field that we use today such as for ex: the
Transistor.
In 1884 Thomas Edison made an observation while working on the incandescent
light. After placing metal plates between filaments Edison notices electricity flowing
from positive side but not the negative. Without a full grasp on his discovery Edison
called it the “Edison effect.” For fifteen years the “Edison Effect” is a mystery until one
of his former assistants is tasked with designing a radio transmitter for Guglielmo
Marconi and in this period of time the Vacuum tube is invented. It was invented in 1906
by Sir John Ambrose Fleming of England and the invention is later referred to as the
Fleming valve.
The Fleming valve is the most basic form of vacuum tubes and it was used in major
inventions of the time period such as the Telegraph. The vacuum tubes were used to pick
up weak signals sent out by the Telegraph across vast distances.
In 1906 a scientist by the name of Lee de Forest made improvements to the
Fleming valve increasing the potential of Vacuum tubes. Just like Thomas Edison, Forest
did not fully understand the potential or capacity of his invention. The invention known
as the Audion tube can not only detect radio signals but it can amplify the electric current
within the tube exponentially. The Audion tube is now used in amplification of all sorts
such as music equipment and radio stations. In 1912 Edwin Howard Armstrong
understands the full potential of the Audion Tube. He improves on Forest’s design by
adding a Triode instead of a traditional Diode. He then used this improvement to invent
the regenerative circuit which can not only pick up radio waves but amplify them. The
circuit could now receive and project the signal loud through speakers without the use of
any head phones which was the case prior to the invention.
(Regenerative Circuit)
In early vacuum tubes the cathode emitted electrons while the anode collected
them. This constant transfer of energy would “wear out” the tube making it not durable.
Lee De Forest noticed this lack of durability and placed a grid between the cathode and
the anode. The emitting electrons then passed through this grid producing a much larger
current flow. The early tubes were still not durable because there was air left over in the
tubes after each use which shortened the life of a tube.
In 1915 Irving Langmuir created a tube design which would be the basis of all
future tube designs. Langmuir’s design is known as the hard valve which made the tubes
last longer, more stable and durable making replacements cost less. In 1927 an American
physicist furthered the efficiency of vacuum tubes by inventing the Tetrode. This
invention eliminates high frequency noise, and expands the frequency range of a tube. A
few years later the Pentode is invented which improved performance at low frequency
and it is the most commonly used valve till today.
During the course of the century there have been many different types and uses
for vacuum tubes. Low voltage tubes have been used in radios and older computers.
Tubes are also used in the recording industry making it possible to record and retrieve
audio from movies. The cathode-ray tube with a focus point on the electron beam lead to
the invention of oscilloscopes, televisions, and cameras. Microwave tubes are used in
radar, and early space communication also in microwave ovens. Storage tubes were used
to store and retrieve data which was essential in advancement of the computer.
There were many people involved in the invention and adaptation of the vacuum
tube some of the important people and their contributions are:
1)
Thomas Alva Edison: Discovers the first
notion about the vacuum tubes and name’s
the concept “The Edison Effect.”
2)
John Ambrose Fleming: Fifteen years
after Thomas Edison’s discovery Fleming
invents the first vacuum tube in 1906.
3)
Lee De Forest: Invents the Audion Tube
which makes amplification of signals
possible.
4)
William D Coolidge: Invents the hot
tungsten filament in x-ray tubes making
deeper x –ray images possible.
5)
Walter Schottky: In 1919 invented the
first multiple grid vacuum tube. He also
discovered the loss of lattice energy within
early tubes.
6)
Irving Langmuir: Discovered the
behavior of electron emission in tubes
which in turn helped redesign future tubes.
Many people know what vacuum tubes are (or have at least heard of them) but
very few people actually understand how they work. The purpose of a vacuum tube is
essentially to convert heat to electricity. Vacuum tubes can also start and stop the flow of
electricity instantly.
Above is a diagram of a simple vacuum tube. A vacuum tube is composed of five
major parts. The cathode (negatively charged electrons) which is the hook shaped part at
the bottom, the grid which is usually horizontal inside the tube, the plate or the anode
(positively charged electrons) at the top of the tube and the heater which is not labeled on
the diagram but it is the “house” shaped part at the bottom of the tube. When the heater
and the cathode are connected or become one part then that part is called the filament.
When a tube is turned on it has a glow to it. That glow is caused by the heater is strictly
provided by the heater and nothing else.
Air is removed from the tube creating a vacuum. The vacuum is created so that
the electrons do not encounter any oxygen, nitrogen or other molecules. When the
cathode is turned on, there is a transfer of energy; electrons at the cathode become
dethatched and move to the anode. The filament can take weak signals and make them
stronger. This process is called amplification. This transfer of energy is how a vacuum
tube works.
The image above is a much more in depth version of a vacuum tube. This
vacuum tube has the five essential parts but also has additional grids and other
components.
Vacuum tubes are used in a wide variety of industries. There three industries that
I will discuss that utilize vacuum tubes are the solar energy industry, the music industry
and the computer industry. Although vacuum tubes are not uses that often in computers
anymore, they were essential to the development of more advanced circuit grids and
smaller machines.
The solar vacuum tube has been around for about 10 years. Solar vacuum tube
panels had a reputation of costing a lot more than flat panel tube but the cost of this has
been driven down due to a higher demand for solar / alternative energy. There is also a
much larger market for solar panels today than there were ten years ago. Some key
points of solar tubes are that they act as a “one-way mirror”. They allow for the sun’s
radiation to come in but it can’t escape. It is also favored over flat solar panels because
of three major things. One, it is able to absorb a lot more or the sun’s radiation.
Statistically, 93% is absorbed and only about 7% is lost due to reflection. Second, flat
panel tubes work much better in lower temperatures than flat panels. Last, the vacuum
walls of solar tubes are able to prevent any loss of energy due to conduction or
convection.
The image above shows how a solar vacuum tube works. The tube absorbs the
sun’s radiation. The radiation flows through the first tube and goes to the inner copper
tube where the hot vapor goes to the top of the tube and cooled vapors flow back to the
bottom of the tube where they repeat the cycle. This is also why in both image above the
tubes are slanted.
Another industry that uses vacuum tubes is the music industry. The music
industry has been using these amps since the beginning. Old radio used vacuum tubes
but even more significant is that the first types of guitar amplifiers were call valve amps.
These amps used vacuum tubes. There has been a switch to electric amp today because
they are cheaper and a little more reliable but as a musician you are looking for sound
quality. These vacuum amps have made a comeback for that specific reason. They
provide a warmer and fuller tone. The way they do this is by adding a boost to the weak
guitar signal by converting heat to electricity; which is the basic principle in vacuum
tubes. These amplifiers are also preferred because they can switch from a clean to a
distorted sound with ease and they are still around because of their sound quality. Below
is an example of what a vacuum tube amp looks like.
Vacuum tubes were first used in computer because of their ability to switch
electricity on and off and their ability to amplify signals but were later replaced by
transistors. Although vacuum tubes helped the advancement of technology by providing
its use in much different application, transistors took over in computers. Tubes are
similar light bulbs, as you can see in the picture above, which means that they have the
ability to burn out sooner and get hot because they generate a lot of heat. Transistors
were preferred in computers because of their small size and longer life span. Modern
machines would not exist if it weren’t for transistors.
Some may argue that the disadvantages of vacuum tubes out weigh the
advantages of them; however, without vacuum tubes we would not have modern
technology such as computers. Yes they’re heavy, generate a lot of heat, take a while to
warm up and require a lot of power but their performance outweighs their negatives.
They can be replaced easily if they break or get damaged. They can be used in a wide
range of applications. They also provide better quality in several industries such as the
solar energy industry and music industry.
The Vacuum Tube
Arjun Duggaraju
Yonathan Ayalew
English 2116-007