#1
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Is it possible to know the SPEED of electron emission
in a Cathode ray tube? Must be extremely fast. If given in miles per hour or kilometers per hour, I can't even fathom what it would be.
Surely someone knows... |
#2
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Actually the beam is under constant acceleration from the time it leaves the gun till it hits the screen. The higher the HV, the higher the acceleration and the higher the final velocity. I dunno what the final velocity is, but it's really honkin' on.
Bill(oc) |
#3
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The speed of light is ~3*10^8 m/s and
In general.... The speed of electrons through free space is affected by their energy, therefore their voltage. A CRT where the high voltage is about 30 kv will have the electrons traveling something like about 0.30 (About 1/3) the speed of light. The greater the high voltage the faster the electrons will travel. |
#4
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Incredible. Thank you both. Does G2 voltage affect the speed of emission ?
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#5
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Quote:
John |
Audiokarma |
#6
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Quote:
While it may seem odd, the region past this last electrode inside the bell region is basically field free because it is all at the same potential. John |
#7
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Wow!!!
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#8
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Wow is right. I keep asking these " obscure " type questions because they are the type which interest me the most in this hobby. The stuff you rarely hear about.
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#9
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A little followup.
The attached photo is of a gun from a 12LP4. The first cylinder on the left is G1. The heater and cathode are located inside of G1 and are not visible. Next is G2. The third cylinder is G3 or the accelerating grid or anode. Whatever you prefer to call it. You'll notice that it has no leads going to it. On the right hand end it has spring contacts that press against the aquadag to make contact with the HV. At the end of G3 is a small hole where the electrons exit. It's at this point that they attain their maximum energy/velocity. John |
#10
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Quote:
Bill(oc) |
Audiokarma |
#11
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A Reference
From "Electronic Fundamentals and Applications", John D. Ryder, 1964.
"Since the electron beam striking the screen is carrying negative charge and the screen is insulated by the glass, the removal of this charge is necessary; otherwise the potential of the screen would fall to such a negative value as to repel the beam. Fortunately, as the electrons strike the screen they not only cause the screen to give off light but also to emit other electrons. This effect, known as secondary emission (see Chapter 3), may result in an average of more than one secondary electron being emitted per electron in the beam. The secondary electrons are attracted to a graphite coating placed over the interior bulb walls and connected to the second anode. As a result, instead of the screen acquiring a negative potential, it may be a few more volts positive with respect to the second anode." |
#12
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But this is true only below second crossover, the voltage at which the secondary emission ratio of the insulator again becomes unity. Aluminized crts overcome this problem and allow landing energies at the screen at almost full anode potential rather than the "sticking potential" determined by the secondary emission properties of the phosphor.
jr |
#13
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It's true that aluminization overcomes this problem.
Potassium silicate is normaly used in the deposition of the phosphor. Strong silicate solutions, or evaporated magnesium oxide, allows them to adjust the second crossover point to closely follow the applied anode voltage. A B McFarlane 1957 Br. J. Appl. Phys. 8 248-252 John |
#14
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Ahhh Yes! nothing like a little MgO to fix up the old droopy secondary emission curve.
jr |
#15
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Some interesting material can be found in the first few pages of this book:
http://www.pmillett.com/Books/hoag.pdf Especially the fact that relativistic corrections (to account for the increase of mass at high velocity) are required above 7000 volts. |
Audiokarma |
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