Talk:Hot cathode

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Near the beginning, the article says: The increased thermal motion of the metal atoms knocks electrons out of the surface. I suppose this is right, but it sounds a little strange to me. Later in the article: The cathode heats to a temperature that causes electrons to be 'boiled out' of its surface into the evacuated space in the tube, a process called thermionic emission. sounds better. As long as the valence electrons are in thermal equilibrium with the rest of the atom, they gain energy at higher temperature. The boil analogy, where in the energy distribution, the higher energy ones escape, seems physically more accurate. Gah4 (talk) 20:50, 9 September 2016 (UTC)[reply]

An interesting point. My feeling is that the "knocking" sentence gives a more concrete picture than the "boiled out" sentence for the vast majority of readers, who are not going to be familiar with concepts like the energy distribution of electrons in metals. Also the process of thermionic emission does not really resemble a pot of liquid boiling on a stove, with bubbles of vapor and convection currents, which is the image the word "boiling" brings to mind. I'm not suggesting removing the "boiled out" sentence, I just think the "knocked out" sentence should be kept too. --Chetvorno^TALK 21:39, 9 September 2016 (UTC)[reply]

I think the main thing I don't like about it, is that it sounds like one atom knocks into an electron. In a slowly boiling pot of water, most molecules just come off the surface, but yes most people think of rapidly boiling. Knock works well for photoelectrons, where one photon supplies the energy to one electron. For thermionic emission, you raise the average energy for all electrons, those with slightly more than the work function, the tail of the distribution, escape. Since the work function energy is subtracted, the actual energy of the leaving electron is pretty low. Gah4 (talk) 22:37, 9 September 2016 (UTC)[reply]

But on the atomic scale all this DOES work by atoms "bumping" into each other, and into electrons. Atoms in the metal lattice transfer heat energy by interaction of their electron shells. The process is quantum mechanical, involving transfer of phonons of vibrational energy, but it is stochastic and a good picture of it is that the atoms "bump" into each other, leaving different atoms with different amounts of vibrational energy at any given instant. An electron near the metal surface will only leave the surface if it gets "knocked" hard enough, so it receives enough kinetic energy to overcome the work function barrier at the surface. As you say, its remaining energy after leaving the surface will be the difference of those energies. --Chetvorno^TALK 07:20, 23 November 2016 (UTC)[reply]

in a friendly way to make an analogy to clarify why calling cathode rays "electrons" is wrong

1)when the cathode of a "thermionic emission cathode ray tube" is heated, the vapor pressure of the cathode metal is reduced significantly so that metal vapor atoms evaporate from the metal cathode,

if there is no electrostatic potential between the electrodes of the tube, then the metal vapor atoms simply fall downward from the force of gravity.

but if the cathode is charged with negative electrostatic potential with respect to the anode. then the atoms that evaporate from the negatively charged hot cathode , will be negatively charged just as if the cathode was being broken into pieces(which it actually is).

the negatively charged metal vapor atoms will be attracted with a force in the direction of the positively charged anode.

but if the charge is not significant, then the negatively charged atoms will yield to the force of gravity and always fall downward.

so if you tilt the tube so that the anode is above the cathode when the charge is low enough. then even though there is an attractive force on the charged vapor atoms, they will still fall downward and never reach the anode.

i say this to emphasize that the atoms are just pieces of charred metal whole atoms with a tremendous mass but with an electrostatic charge ,, just like tiny pieces of paper attracted to a comb that has been electronically charged by combing hair,, if there is enough electrostatic charge, then the pieces of paper will float upward and stick to the comb if there is enough charge

back to the charged vapor atoms

yet, if there is significant charge , then the attractive force on the atoms will overcome the force of gravity and the atoms will move toward the anode irregardless of the orientation of the cathode and anode.

and interestingly. the atoms will speed up as they approach the anode but they will also receive a greater and greater attractive force as they approach the anode.. the force will be equal to the inverse of the square of the distance.

this is the only methode by wich the "tube" can transfer electrons from the cathode when the cathode is electrostatically charged negativly with respecvt to the anode. the cathode metal atoms evaporate because of the heat lowering the vapor pressure of the cathode's actual metal they keep the electrostatic charge after they evaporate off of the cathode . the anode plate is positively charged. the negatively charged metal atoms are attracted to the positively charged anode plate by the electrostatic charge.. but if the charge is insufficient. the atoms yield to the force of gravity and fall downward. so the physical orientation of the cathode and anode with respect to gravity is a factor .. but if there is sufficient electrostatic attraction to overcome gravity,, from sufficient voltage potential on the anode,, the cathode's negatively charged metal vapor atoms will move toward the anode accelerating as a force of the inverse of the square of the distance from any specific metal vapor atom to the anode plate accelerating with more and more force going faster and faster toward the positively charged anode plate until finally, physical contact is made by the negatively charged cathode metal vapor atom to the anode plate, at the point of inevitable physical contact with the anode plate, the contact of the electrostatics charged metal vapor atom to the anode plate, produces a momentary covalent bond (like the bond between metal atoms in a conductive wire). at that moment, the electrostatic charge is equalized between the vapor atom and the anode plate, thus transferring the electrostatic charge from the cathode to the anode. the external power source pushes the electrons back threw the wire,, and any connected circuits,, back to the cathode threw the circuits. well that may be confusing, but anyway,,

if a metal screen is placed between the cathode and the anode , close to the cathode with respect to the anode, then if the screen is connected to a wire and the screen can be negatively charged threw that wire.. then it can be charged negative enough to overpower the anode's positive electrostatic attraction on the metal vapor atoms, thus holding the negatively charged metal vapor atoms back and preventing them from traveling toward the anode ,, in this case, the flow of electrons threw the tube(via the metal vapor atoms) and consequently threw any and all circuits between the tube and the power supply as well.

a small amount of electricity is enough to charge the screen enough to completely stop the flow of electrons from the cathode to the anode. controlling the electrostatic charge on the screen uses only a fraction of the amount of electricity that flows from the cathode to the anode threw the metal vapor atoms. this is all relative to the fact that the voltage on the screen, controls the amps of current threw the metal vapor atoms. but remember. it's whole atoms that move threw the tube, not electrons.

thanks for reading. love jonathan scott james — Preceding unsigned comment added by Jonathan scott james (talk • contribs) 05:27, 23 November 2016 (UTC)[reply]

1. Prolonged hot standby with zero cathode current (cathode interface)
2. Prolonged underheating

on the cathode coating in concrete terms? 85.247.227.47 (talk) 18:13, 15 July 2017 (UTC)[reply]

I reverted a mention of a "half indirectly heated cathode". I had never heard this name before, and a google search finds only two patents, one from Germany in 1941, and from China more recently. But that is only the title, I don't see a description of what they actually do. My first thought was a cathode that is direct on one side, and indirect on the other. I do believe that it is usual to keep the potential difference small, to avoid conduction between the heater and cathode, and they can be either pins in common, or separate pins connected as appropriate externally. There are complications with AC heater current and coupling to the cathode, so one needs to be a little careful. Gah4 (talk) 19:24, 15 July 2017 (UTC)[reply]

There are lots of fan sites for everything; we don't normally link to them in WP unless they provide some unique information that can't be gotten into the encyclopedia in any other (licence-compatible) way. I dont' think a fan site discussing the details of which voltage were used at which times is terribly informative to the reader. A brief discussion of *why* there were different heater voltages would be much more worth while, instead of a trainspotter's guide to which numbers came in which tubes. --Wtshymanski (talk) 19:37, 10 October 2017 (UTC)[reply]

I read through much of it, and there are many more details than the voltage thing. I first got interested in electronics in the 1960's, when tubes were still around, though most new things used transistors. I had tube data manuals to the 1940's or so. But there are a whole series of earlier tubes not commonly described, that this article discusses, and in much more detail than just the filament voltages. I have known for years that the 6.3 volt filament, and so the common transformer secondary, was related to lead acid battery voltages, but nothing from earlier. I suppose it would be more applicable to an actual vacuum tube article instead of a hot cathode article, though. Gah4 (talk) 23:04, 10 October 2017 (UTC)[reply]

Agreed, it's more relevant to tubes than to this article. --Wtshymanski (talk) 15:29, 11 October 2017 (UTC)[reply]

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