Oleg Vladimirovich Losev (Russian: Олег Владимирович Лосев) was none other then the first person to record his findings in regards to Light Emitting Diodes (LED).Though he only lived to be 39 years old (May 10, 1903 – January 22, 1942) he had an impressive resume. Unfortunately for him, for Russia, and for electronic advances the Russian government did not take him seriously.
While Oleg discovered that a carborundum (silicone/carbon compound) point-contact junction (cats whisker) diode used in crystal radios produced light when current was passed through it. Thus was the first LED. Oleg published his findings in a Russian Magazine in 1927 but the LED was not a practical electronic component until 1962.
Mr. Losev also conducted experiments with negative resistance in semiconductor junctions and built the first solid-state amplifiers, oscillators, and superheterodyne radio receivers 25 years before the transistor was invented.
Just think of how much further Amateur radio and all other radio services might be today if Oleg Losev had been taken seriously in his time. It just makes me wonder what our ham shacks would look like today.
In 1895 Alexander Stephanovich Popov built an improved version of a coherer-based radio receiver designed by Oliver Ledge. It proved to be a good lightning detector. Whether or not he used it in conjunction with a spark gap transmitter to publicly demonstrate the transmission of a radio signal between two buildings on March 24, 1896 (Marconi did a public demonstration in September 1896) seems to be questionable. To this day Russia says that Popov, a Russian, was the inventor of the radio. One thing that can not be argued is that Oleg Vladimirovich Losev, a Russian, was the inventor of the LED.
As we saw in earlier posts the diode vacuum tube (or valve) became a triode by inserting a grid, known as the control grid, which allowed it to amplify audio and RF signals. The triode had a problem of interelectrode capacitance which limited the frequency at which it would operate properly. By adding another grid the triode became a tetrode. The second grid, called screen grid, has a positive DC bias but an AC ground via a bypass capacitor.
The tetrode was an improvement over the triode but it had a problem with secondary emission.
When the electrons pass the positively biased screen grid they speed up then when they strike the plate (anode) they may dislodge another electron and send it into the space between the screen grid and the plate. They may be attracted to the screen grid and establish a current flow from the plate to the screen grid known as secondary emission.
Secondary emission can cause a condition known as negative resistance where an increase of plate voltage will result in a decrease plate current. Negative resistance may lead to unstable operations.
In 1926 Bernhard D. H. Tellegen, a Dutch electrical engineer, inserted a third grid following the screen grid and operated it at ground potential or slightly negatively biased. This grid, called a suppresser grid, prevents the electrons that were creating the secondary emission to be attracted back to the screen grid. Thus the pentode, five electrode, tube was born.
Both the tetrode and pentode tubes have high power sensitivity when compared to the triode tubes with the same power output.
Another tube designed to reduce unwanted secondary
emission is the beam power tetrode. Instead of a suppressor grid it has beam-focusing plates that are run at ground potential or slightly negative
potential. They follow the screen grid and cause the electrons to flow in a narrow beam to the plate thus pushing any potential secondary emission electrons back to the plate. The beam power tubes are usually used as power amplifiers for RF and Audio. The 6146 was a very
commonRF final amplifier beam power tubes used by ham radio operators in the 1950s.
Many of the linear amplifiers used by amateur radio operators still use vacuum tubes.
The last post was about the vacuum tube diode. I forgot to mention for you European and other readers when I speak of a vacuum tube it might be what you call a valve. The term valve is a very good one because it really is an electron valve. Diodes, as well as all vacuum tubes, are electron check valves. A check valve for liquid will allow the liquid to flow in one direction but blocks it from flowing back. That is the same thing a diode does with the electron flow in a conductor.
Adding a grid to a diode is like adding a gate with a stem and knob to the check valve. The gate will allow the operator increase or decrease the rate of flow. For many years effective state of the art amateur radio equipment was made possible by the grid or as we will see later multiple grids.
If you don’t know how a diode works then I might suggest you back up to the previous post and read it.
John Ambrose Fleming, an English physicist, worked as an engineering consultant for several firms including Edison Telephone and the Marconi Company. In 1904 Fleming conducted some experiments using Edison effect bulbs he had imported from the USA. He found the bulbs could be used as rectifiers which he called “oscillation valves”. Because of their greater efficiency and the fact that a hot spot did not have to be found the vacuum tube diodes detector soon started replacing the crystal detectors in radio.
Just as an interesting side note, though we think of the vacuum tube radio as the predecessor to the solid state radio the crystal detector was actually a solid state diode and thus the solid state radio preceded the vacuum tube radio.
Amplification and oscillation were not possible with the diode vacuum tube.
Lee DeForest has been credited adding a third element called a grid to the vacuum tube and making what he called the “Audion Tube” which is the forerunner of the triode.
The grid is a wire mesh placed between the cathode and the plate. Electrons are able to flow past it with very little effect if it is not biased (bias means to apply a voltage). When a positive voltage is applied to the grid (positive bias) the electrons will flow faster and the plate current will increase. The grid will collect some to the electrons as the others pass by it and so there will be a grid current. Most of the time grid current is not desirable.
When a negative potential is added to the grid (negative bias) the electrons are
repelled by the negative field around the grid wires and thus less will pass through the mesh. By increasing the negative potential the repelling effect will cause fewer electrons to pass. This effect will continue to increase as the negative bias is increased until the current is shut off completely. A very small voltage change on the grid can cause a large change in current flow inside the tube so amplification is possible. As the small signal goes negative it is added to the negative bias voltage and thus decreases the output, the plate voltage will go more positive, then when the signal goes in the positive the grid bias voltage will decrease so the plate current will increase causing the plate voltage do decrease so the small signal will produce a larger signal but with a 180 degree phase shift.
By taking some of the signal output and feeding in back into the input of the amplifier an oscillator can be constructed. This made it possible to create a continues wave (CW) oscillation which is the fundamental foundation of all ham radio, commercial radio, and any other radio communications
A new problem was added with the triode so that another element needed to be added but I will save that for the next post.
To start understanding the operation of the vacuum tube we must start with the diode meaning two elements or two electrodes. These two electrodes are the cathode and the anode more commonly known as the plate. There is the requirement of a heater which may also serve as the cathode but many diodes have the heater inside a sleeve so it will heat the sleeve which is the cathode. Though the heater is separate from the cathode it is not counted as an element.
As the cathode heats up to red hot the molecules are vibrating so vigorously they cause some to the atoms to lose electrons. These free electrons form an electron cloud around the hot cathode. When a negative potential is placed on the cathode the field will become greater, that is to say more intense and more electrons inter into the electron cloud.
If the cathode was not in a vacuum the electrons cloud would be dissipated by the gas molecules. Thus it is placed inside an evacuated envelope (glass or metal).
A plate is also included inside the envelope. The term plate, I fear, gives a miss conception of what it looks like. The plate is usually a cylinder that is placed around the cathode (see the above drawing). If a positive charge is placed on the plate the free electrons will migrate across the gap to the plate thus producing a current flow.This process is known as the Edison Effect.
If a negative potential is placed on the plate that is negative with reference to the cathode thus leaving a positive cathode and negative plate current will not flow. This is the principle of rectification. The part of the cycle that causes the cathode to be negative and the plate positive current will flow but when the reverse happen and the plate is negative and the cathode positive current will cease thus turning the AC into a rippling DC voltage.
When the diode is used to produce DC from AC filters must be added to eliminate the AC ripple. The raw DC output is a single diode will rise and fall as the AC voltage rises to a peak and then fall back to zero volts. Then there will be no current flow during the second half of the cycle. Thus if only one tube is used it is called a half wave rectifier. Four diodes can be used in a bridge rectifier circuit or by using a center tap on the transformer two tubes can be used to make a full wave rectifier. A smaller filter can be used when a full wave rectifier is used to produce a clean DC voltage.
Vacuum tube rectifiers are not common in modern ham radio equipment but when I became an amateur radio operator in 1960 they were very common in new amateur radio equipment.
There is a lot of talk about the old days and vacuum tubes. It would seem that some hams think there is no place for the vacuum tube. It was recently that I was talking to my grandson, a radio technician in the U. S. Navy, and I asked him about the high power transmitters and he told me that they all had tube finals.
Looking through amplifiers to boost the power output from a transmitter or transceiver I was not able to find any solid state amplifiers above 400 watts. I am not saying there aren’t any and I did not do an exhaustive research but I did look at several sites, thumbed through QST and saw several amplifiers. So most modern amateur radio stations running 500 watts or more are using one or more vacuum tubes.
The vacuum tube is a simple device but I think they might make an interesting subject because for one there are still a lot in use in ham radio, whether in vintage equipment or power amplifiers. Reason number two there are a lot of new hams today who have had no experience with vacuum tubes and would just find them interesting. And finally reason number three is vacuum tube amplifiers are easy to understand and thus they make it easier for wanting to understand amplification and oscillation to learn the vacuum tube version first then the solid state will be much easier to comprehend.
So I have decided to do a series on the vacuum tube over the next few days.
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12/20/2012 Sutter County California will have a simulated leave break and thus flooding. For this drill they asked for amateur radio participation. They did have one stipulation any ham radio operators participating must have completed the ICS 200b course. I am sure there are some who have to work that have completed the course and are thus not able to help but there are others who have the time but have not completed the course and thus are not allowed to participate.
The government agencies are getting serious about this. Some hams think their services will not be refused is a real disaster hits but do not kid yourself. They do not want people who do not understand the Incident Command System operational procedures to mess up the works. There is a very good possibility that ARES may require ICS 200b to be a member.
I would also recommend taking the ICS 700 and the ICS 100b.
We will only have 3 amateur radio operators at the drill and this makes amateur radio look bad. It makes the county officials question whether or not we will be able to help out in a time of real need.
To find the ICS 200 b course [CLICK HERE]
To fine the ICS 100 b course [CLICK HERE]
To find the ICS 700 course [CLICK HERE]
Do you know a ham radio operator you would like to buy a gift for but don’t know what to git? Here are a few suggestions:ham radio, amateur radio, gift, amateu
Maybe you are an amateur radio operator that knows someone who might buy a gift for you then you might direct them to this post.
For young people you would like to encourage to become an amateur radio operator here are few suggestions:
As the years passed and radio communications engineers tried to produce transmitters and receivers that would work effectively at higher frequencies. The interelectrode capacitance was the largest limiting factor for the upper frequency a vacuum tube would work. So through the years various designs of tubes were made in an effort to reduce the interelectrode capacitance.
As you probably know anytime there is are conductors separated by insulation
there is capacitance formed by this configuration. The cathode, the grid or grids, and the plate are all separated by a vacuum which is an insulator. This is what is meant by interelectrode capacitance. As the frequency of operation is increased the capacitive reactance of the interelectrode capacitance decreases thus reducing the tubes ability to amplify.
During the late 1930s a small triode was constructed which was shaped much like an acorn. The leads, which also produce problems as the frequency increases because they too have capacitance, came out sideways from the tube thus reducing the lead capacity and the small size reduced the interelectrode capacity. Later tetrodes and pentodes acorn tubes were added to the list.
The 955 was one triode acorn tube which the data published on it said the tube would work from 4 to 600 MCs (MHz) but there were circuits using these tubes operating in the 900 MCs.
The acorn tubes were used in VHF and UHF circuit design up until the late 1940s.
An other interesting tube design that could work at a little higher power then the acorn tube, about 150 milliwatts, and much higher frequency, 3.3 gigacycles (gigahertz), was the lighthouse tube. The lighthouse tube made its debouch in the 1940 and continued to be used in new radio design up until the early 1970s.
The name lighthouse tube is, like the acorn tube, derived from its appearance. The lighthouse tube has the filament and cathode near the base of the tube which fit into an octal socket. The grid sat above the cathode and was accessed by a ring around the tube. Finally the plate was at the top of the tube and was connected to a plate cap. Each succeeding section of the tube was smaller in diameter thus giving an appearance that was similar to a lighthouse.
Most of the radios that made their way into ham radio operations was via amateur radio operators purchasing military surplus units which for several years after WWII were readily available for very low cost.
Surface Mount Technology (SMT) is a common way of adding electronic components to a Printed Circuit Board (PCB) without placing leads through holes drilled in the boards. The components are known as Surface Mounted Devices (SMD) or Surface Mounted Components (SMC).
Many of our modern ham radio transmitters, receivers, transceivers, and other peripheral devices use this technology. Most hams are reluctant to try to repair units with SMD components and if an amateur radio operator is unfamiliar with soldering technique on these tiny electronic components it is probably best not to try.These devices include resistors, transistors, capacitors, ICs, coils, and more.
It really isn’t hard but it does have to be done right.
Never try to reuse components that have been removed from the board because the process of removing them will frequently damage the components.
I worked commercial radio repair for several years repairing units with SMD components so from a professional point of view I can recommend the following video for those who would like to know how to remove and replace SMDs.
To watch video [CLICK HERE]