It's going to be a long hot summer. Can't wait to hear the explanation for the voltage gradient within the electron path.
All good fortune,
Chris
All good fortune,
Chris
I can't wait to hear your explanation as to how electron acceleration & flux remains essentially constant despite the changing anode current, and how come the load line is never straight.
(clue:- the extremely low efficiency of triodes, compared with pentodes/beam tetrodes).
A perfect example of my argument is a typical TV damper diode.
It quotes voltage drop of 16V at 350m/a, which makes it clearly have a DC resistance of 45ohms.
But in a diode, the anode is constantly receiving the entire 100% stream of ALL electrons and all the cathode heat.
If that is the case, how come it doesn't get even remotely hot when there is no anode voltage applied, it's getting all those electrons, but nothing happens!
ie. the electrons don't heat up anything!
It quotes voltage drop of 16V at 350m/a, which makes it clearly have a DC resistance of 45ohms.
But in a diode, the anode is constantly receiving the entire 100% stream of ALL electrons and all the cathode heat.
If that is the case, how come it doesn't get even remotely hot when there is no anode voltage applied, it's getting all those electrons, but nothing happens!
ie. the electrons don't heat up anything!
So, current is flowing with no voltage applied. A perpetual motion machine of the second type! Get your white tie suit ready to meet the king of Sweden.
When there is no anode voltage applied, the electrons hardly have any kinetic energy when they hit the anode, so they also can't heat up the anode much.
By the way, 1 m/a is one metre per annum, so about 31.69 nm/s.
This statements disqualify any student or elementary schoolboy from passing the physics exams ... 😀
A little problem. Hot cathodes emit electrons whether or not there is current flowing. That is what the heater is there for. Turn off the heater when an amp is running and the sound gently fades away, and fades back in when you turn the heater back on. So whether or not there is a potential difference in the anode>cathode it still emits electrons, which is why electron flow is irrelevant to anode dissipation. In effect the cathode will always produce the same number of electrons (within reason). In a valve based diode, Anode dissipation is directly related to current,- got nothing to do with electrons or their velocity, because the voltage drop across the diode scarcely changes.
Sarcastic, perhaps you could make the effort to learn rather than assume or get a notion of how things work based on some unfortunately flawed view. I'm sure there may be simpler texts to learn from, but if you have a physics background then the 1962 RCA Electron Tube Design book is an excellent reference, especially the Space Current section for what you appear to be missing an understanding of. (File:RCA Electron Tube Design 1962.djvu - Wikimedia Commons)
In a valve diode, the velocity of electrons is directly related to potential difference. (high attraction = large voltage.) The number of electrons in the space charge cannot change. The anode dissipation is a direct function of internal resistance and current. The internal resistance is not a fixed value. eg. In a triode the PD between anode and cathode is in inverse proportion to the current transferred. The number of electrons available doesn't change. The grid in there simply prevents them from leaving the K-g1 interface. A triode is a diode with one extra electrode, to control the diode flow. The triode is singularly inefficient because it doesn't have a screen grid (real anode) to accelerate the electrons.
What I am attempting to get you to understand, is simple. E=Mc2, so velocity of electrons is not the ONLY thing that determines Anode dissipation (energy), you have MASS(quantity) as well as velocity. They are not the same as regards current flow, electrode spacing, secondary emission and a load of other things going on in there which influence the plate resistance.
Yes. More current = more electrons hitting the plate.
Anode resistance is not a physical resistance, it is irrelevant.
E = mc^2 is not relevant here since we are not interested in the rest-mass energy, just the kinetic energy. If we had positrons as well, annihilating the electrons, then that would be relevant!
At heart its very simple, an electron acquires kinetic energy equal to eV, and then dissipate that energy into the target electrode, releasing eV there as heat (and a small fraction of secondary emission, X-rays, etc).
V is the potential difference, e is charge on the electron.
Thus the power = IV, since the electron flux = I/e electrons/s, so the energy per second is (I/e)eV.
The actual formula for kinetic energy is irrelevant, which is just as well because its complicated by the possibility of relatavistic speeds. At low voltages the (mv^2)/2 formula is a reasonable approximation, but above 1000V or so you'd start to need relatavistic corrections
The "resistance" of a tube is a notional thing, there is no resistance in a vacuum - current is determined by space-charge and emission characteristics, neither of which are dissipative effects. The space charge can act to choke electron flow at higher currents as it modifies the electric field distribution, thermionic emission rate simply limits the maximum electron flow available.
You can make a gravitational analogy, with balls being dropped through a height into a poll - the gavitational potential energy (mgh) is converted to kinetic energy as they fall, and then released on impact - you can calculate the velocity at impact from the kinetic energy formula, but this isn't needed as you know the total kinetic energy is mgh at that point. If the mass flow is F, the total power is (F/m)mgh = Fgh, analogous with IV, since gh = gravitational potential difference.
sarcastic1 you have failed basic physics 🙂
At heart its very simple, an electron acquires kinetic energy equal to eV, and then dissipate that energy into the target electrode, releasing eV there as heat (and a small fraction of secondary emission, X-rays, etc).
V is the potential difference, e is charge on the electron.
Thus the power = IV, since the electron flux = I/e electrons/s, so the energy per second is (I/e)eV.
The actual formula for kinetic energy is irrelevant, which is just as well because its complicated by the possibility of relatavistic speeds. At low voltages the (mv^2)/2 formula is a reasonable approximation, but above 1000V or so you'd start to need relatavistic corrections
The "resistance" of a tube is a notional thing, there is no resistance in a vacuum - current is determined by space-charge and emission characteristics, neither of which are dissipative effects. The space charge can act to choke electron flow at higher currents as it modifies the electric field distribution, thermionic emission rate simply limits the maximum electron flow available.
You can make a gravitational analogy, with balls being dropped through a height into a poll - the gavitational potential energy (mgh) is converted to kinetic energy as they fall, and then released on impact - you can calculate the velocity at impact from the kinetic energy formula, but this isn't needed as you know the total kinetic energy is mgh at that point. If the mass flow is F, the total power is (F/m)mgh = Fgh, analogous with IV, since gh = gravitational potential difference.
sarcastic1 you have failed basic physics 🙂
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"At heart its very simple, an electron acquires kinetic energy equal to eV, and then dissipate that energy into the target electrode, releasing eV there as heat"
Sadly for you I worked in nuclear physics, and I can assure you, the electrons simply do NOT have enough mass or energy inside a valve to heat the anode.
In a sychrotron we accelerate particles to MeV, then we are talking, when it hits the target.
We can get some serious joules of energy to knock bits of atoms off.
The problem with your inability to understand the basic physics is that the heat CANNOT come from the electrons, it can only come from an impedance. (which is simply a conversion of a resistance in dynamic terms).
Ie, if you put 300V on the anode of a 12AX7 with the anode impedance of 62K you get 4.8m/a current which equates to 1.5W.
Where do the watts come from?
By the simple fact the anode looks like a whopping great 2W resistor to a DC supply.
Nothing to do with the tiny number of electrons swopping places, it's simple current and voltage regulated by the space between the different electrodes.
It might be hard to understand a vacuum can represent a resistor in this way but it does, just as does a cold discharge voltage regulator. (in whatever gas gives the best voltage for the application).
150V at 0.010A = 15K, so if you lower the current it can look like 30k no heater whatsoever.
Constant voltage, variable current.
Funnily enough it gets hot,- 1.5W of heat at 10m/a in a small glass, the big ones quite a bit hotter at 6W in big glass.
It's not the electrons heat it up, it's the voltage drop x the current, same as a normal valve.
Sadly for you I worked in nuclear physics, and I can assure you, the electrons simply do NOT have enough mass or energy inside a valve to heat the anode.
In a sychrotron we accelerate particles to MeV, then we are talking, when it hits the target.
We can get some serious joules of energy to knock bits of atoms off.
The problem with your inability to understand the basic physics is that the heat CANNOT come from the electrons, it can only come from an impedance. (which is simply a conversion of a resistance in dynamic terms).
Ie, if you put 300V on the anode of a 12AX7 with the anode impedance of 62K you get 4.8m/a current which equates to 1.5W.
Where do the watts come from?
By the simple fact the anode looks like a whopping great 2W resistor to a DC supply.
Nothing to do with the tiny number of electrons swopping places, it's simple current and voltage regulated by the space between the different electrodes.
It might be hard to understand a vacuum can represent a resistor in this way but it does, just as does a cold discharge voltage regulator. (in whatever gas gives the best voltage for the application).
150V at 0.010A = 15K, so if you lower the current it can look like 30k no heater whatsoever.
Constant voltage, variable current.
Funnily enough it gets hot,- 1.5W of heat at 10m/a in a small glass, the big ones quite a bit hotter at 6W in big glass.
It's not the electrons heat it up, it's the voltage drop x the current, same as a normal valve.
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For a good understanding of phenomena , in a resistor it is the same , at least some of the accelerated electrons hit the atoms inside , slow down , lose kinetic energy and accelerate again , this is how the energy is lost . We just call resistor a material that cause more or less of this hits to occur .
This is why you can apply the Ohm's laws for tubes , even if electrons travel through vacuum not wires and there is no physical resistor . Or just hitting a surface with electrons produces a "resistor" there ,if you like
This is why you can apply the Ohm's laws for tubes , even if electrons travel through vacuum not wires and there is no physical resistor . Or just hitting a surface with electrons produces a "resistor" there ,if you like
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