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Which is better directly heated cathode or indirectly heated cathode?
Wiki User
∙ 10y ago
A cathode to which heat is supplied by an independent heater element in a thermionic tube; this cathode has the same potential on its entire surface, whereas the potential along a directly heated filament varies from one end to the other. Also known as equipotential cathode; heater-type cathode; unipotential cathode.
Wiki User
∙ 13y ago
Wiki User
∙ 10y agoThat depends on a number of factors.
Directly heated cathodes heat up faster resulting in quicker turn on, but must be powered with DC (AC would cause hum), biasing is trickier as the cathode of all tubes are connected in parallel to the common filament voltage supply, cannot be used in very high power tubes due to the fragility of the filament and limits of it current carrying ability (it has to carry both filament current and cathode current).
Indirectly heated cathodes heat up slower, but can be powered by either DC or AC without causing hum, biasing is easy and large voltage differences between the cathode and heater are allowed as they are completely insulated from each other, suitable for use in very high power tubes.
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Why the cathode in cathode ray tube is indirectly heated by the filament?
To create an electron cloud that can be shaped into a beam.
How does a vacuum tube work?
contains only a heated electron-emitting cathode and an anode. Electrons can only flow in one direction through the device—from the cathode to the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grids.[5]
What is a TRIODE and what are its uses?
A triode is a vacuum-tube (US) aka valve(UK) with three electrodes : an anode, a cathode and a grid. The cathode is heated electrically which boils off a cloud of electrons. The anode is made positive ( typ. 100-500V) which attracts the electrons towards it. The grid is an open structure, usually of thin wires, placed between the anode and cathode, but nearer the cathode. If a negative voltage is applied to the grid the current flow through the tube is reduced. The more negative, the less current. Prior to the development of transistors, tubes were used for all things in radio,TV and electronics. Different tubes had different numbers of electrodes; the triode was particularly suited to high power amplifiers, especially at radio frequencies. Triodes are still used today by shortwave radio stations, and for RF heating equipment.
Why does a diode not conduct in reverse bias?
A diode cannot conduct in reverse bias because of the way it was made. If the question is asking about a thermionic vacuum tube diode, the electrons produced by the heated cathode of the tube can only move in one direction: from the cathode to the anode - but only for as long as the anode is positively charged. The reason is that, if the anode is made to be positively-charged, it ATTRACTS electrons - which are negatively charged - from the cathode, so a current flows from cathode to anode in the "normal" biased direction because of the physical fact that UNLIKE CHARGES ATTRACT ONE ANOTHER. If the anode is made to be negatively charged, the electrons won't go to it because of the physical fact that LIKE CHARGES REPEL ONE ANOTHER, so no electrical current can flow from the cathode to a negatively charged anode. (In fact no electrical current can ever flow from a negative anode to the cathode for an entirely different reason: no anode of any normal thermionic vacuum tube was ever designed and made to "produce" electrons in the way that a heated cathode produces them!) To be able to "produce" electrons and let them fly to the positively charged anode, the cathode must be able to receive some more electrons to replace all the ones that have left the space around the cathode. That "supply of more electrons" is called an electric current. That current does not come from nowhere - it has to comes from a source, such as a battery or a generator - and the electrons which reach the anode must then be conducted back to the battery or a generator so that they complete a full electrical circuit by traveling along the wires which connect the source to the diode. Similarly, because of the way it was made, a semiconductor diode behaves in just the same way as a vacuum tube diode: electrons can flow from the negative end to the positive end of the semiconductor diode but not the other way around. The actual reason why a semiconductor diode works like that is very much more complicated to explain than for a vacuum tube diode. Put very simply, a semiconductor diode has the kind of materials inside it that will only allow electrons to flow one way. If a voltage is applied to the diode the wrong way round (called reverse bias) practically no current can flow through the diode.
What is principle of operation of a multicavity magnetron?
Imagine a tuned cavity i.e. a bell. When it is struck, it provides a sound wave of fixed frequency. If it is struck several times a second, it provides the same frequency at a much higher volume. The striking of the bell is known as the pulse repetition frequency (PRF) and it is this that dictates the power output of a magnetron. The dimensions of the cavities govern the output frequency. Instead of striking a magnetron, it is pulsed across its anode and cathode by a high DC voltage. This is the energy input that equates to the striking of the bell. The gap between the cathode and anode is a vacuum. Electrons being emitted by the heated cathode each time it is pulsed or 'struck' transfer the energy to the cavities. These electrons bunch in reaction to the tuned frequency of the cavities, forming spokes circulating the cathode. Eventually, the electrons strike the anode and cause the cavities to 'ring' at the tuned frequency. One of the cavities has a loop that extracts the energy into a coax/waveguide.
Difference between direct and indirect cathode ray?
In a directly heated cathode, the filament is the cathode and emits the electrons. In an indirectly heated cathode, the filament or heater heats a separate metal cathode electrode which emits the electrons.
Why the cathode in cathode ray tube is indirectly heated by the filament?
To create an electron cloud that can be shaped into a beam.
In the cathode ray tube where do the particles originate?
In a cathode ray tube (CRT), the particles, which are electrons, originate at the heated cathode, becoming the so-called cathode rays. The electrons stream off the cathode and rush over to the anode.
What type of electrode is a cold cathode?
Cold cathode is a cathode, an electrode that emits electrons, which is not electrically heated by an element. Cold cathodes are used in gas discharge lamps such as neon lamps and discharge tubes.
Where did the electrons from cathode ray come from?
In a cathode ray tube (CRT), the particles, which are electrons, originate at the heated cathode, becoming the so-called cathode rays. The electrons stream off the cathode and rush over to the anode.
Why should cans not be heated on a stove?
Unopened can will explode if heated directly on a stove.
Is the earth's atmosphere heated directly by a planet or a star?
Earth is heated by the sun, which is a star.
Why the ethanol heated in a water bath instead of being heated directly?
Because it is inflammable
How does the sunlight warm the land air and water?
Land and sea are heated by absorbing radiant energy from the sun. Air is heated indirectly by being in contact (conduction) with land or water.
The atmospheric gases in the thermosphere are heated by what?
directly by the sun.
Why you heat oil indirectly in redwood viscometer experiment?
SO that the oil cup gets uniformly heated from all the sides
What type of jobs affect the environment?
Nearly all, directly or indirectly. Directly includes farmers, fishermen, miners, oil workers, chemical workers, builders. Less directly factory workers, pilots, train and vehicle drivers, soldiers. Indirectly anyone who works in a heated or air conditioned office, drives to work, eats a beef sandwich for lunch, uses any machine at work So that leaves window cleaners, traffic wardens, lollipop ladies and gardeners.
