The Naked Scientists

The Naked Scientists Forum

Author Topic: How trustfully is the actual explanation of diode tube working?  (Read 5546 times)

Offline sorincosofret

  • Sr. Member
  • ****
  • Posts: 204
    • View Profile
How trustfully is the actual explanation of diode tube working?

I will start this post with a comparative example.
 Letís suppose there is a golf device able to throw the balls with speed of km/s, having a small reserve of balls attached to it. There is also a child having a speed of 1 m/s, which collects one ball per trip, and tries to refill the reserve as in fig. 1


Figure 1. Comparative example
 
With the maximum rhythm of device throwing, the child canít insure a stationary level of balls in reserve, and after a certain time interval, there are no balls in the device reserve, and all balls are sparse on the field.
    What kind of relation can be between a golf device and a gas tube (old diode type)?
There is a simple analogy between the golf device and whatís happened in a gas tube.
There is an electrode that throw away electrons with a great speed (decades of km per second) and there is recirculation electron movement which tries to ensure this need of electrons as indicating in the simple circuit 2.




Figure 2. Simple diode circuit

The problem is represented by the great difference between electron speeds in gas tube and electron speeds in a metallic conductor. According to actual interpretation an electron has in metallic conductor a speed of mm per second.
Letís consider an old tube diode in a simple circuit formed as in fig 2, and a current intensity of 15 mA at a source voltage of 25 V.
A current of 15 mA means in every second a number of:
n = 15*10(-3)/1.6*10(-19) =9.3*10(15) electrons pass through a transversal section of the metallic conductor.
In order to have a continuity of electric current the same number of electrons must pass through any transversal section of diode tube.
But here appear a problem. The speeds of electrons in the tube are enormous related to the electrons speeds in conductor.
As consequence some peculiar effects should appear at cathode and anode.
In a normal ,,comportmentĒ, after few seconds of diode working, due to accumulation of negative charge on anode and in near neighborhood, the anode canít accept all electrons emitted from cathode. On the anode negative charges appear, and cathode remains positively charged.
Practically, a diode after few second of working in a direct continuous current should become a capacitor, and depending on the resistance of the circuit, after a smaller or longer time interval, the current should stop circulate in the space between electrodes.
These are theoretical prediction of actual electromagnetism. Does this happen in reality?
It is well known a diode can work for weeks without this capacitor effects in DC and this neck bottle effect does not appear.. It is necessary to make the specification that experiments are made in DC and not in AC where the things are a little bit more complicated.
Having the same circuit and two ammeters one in cathode circuit and another in anode circuit, letís suppose at a certain time the circuit is switched off in cathode circuit (fig.3).



Figure 3.

It is clear that this gap in the electron flow will impede other electrons to be emitted from cathode.
But, the charge already accumulated in anode and anode neighborhood should circulate further for a certain time in order to be neutralized by positive potential of DC source.
In this case, depending on the anode circuit resistance, a current should be registered for a longer or shorter time, according to actual electrodynamics. Does this happen in reality?
Again there is no such bottle neck effect observed in about half a century of vacuum diode working.
This is only a superficial approach, because the vacuum diodes are part of physics history. But for a detailed analysis a comparison between a vacuum diode and a Klystron should be made. Why a vacuum diode does not emit microwave? The working principle is the same Ö


 

lyner

  • Guest
Are you intending to visit absolutely every branch of Science and give it your quaint treatment?

That last statement of yours is nonsense. A klystron works because of resonant cavities. A diode has none. Both exhibit the interaction between charges and em waves, one uses it to provide amplification and its design enhances this interaction, the other does not make a point of it. Do you not realise that electrical energy from the power supply (a flow of energy via an electric field) causes the acceleration of an electron. When it slams into the other end, the ke is transfered, via an elecromagnetic interaction as it collides with atoms, to internal energy.
What is it exactly that is not happening?

As for the rubbish about what happens to the charges in a diode. The Cathode gets a positive charge, does it? It repels the electrons because the power supply gives it a negative charge and the anode is given a positive charge by the power supply. There is available energy and it is transfered. What's the problem?

If you just heat up the filament, the electrons hang around because of the small level of positive charge on the surface atoms - but that's not diode action. That's just thermionic emission.

I have yet to see you turn up with anything which is actually NEW!
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8644
  • Thanked: 42 times
    • View Profile
Never mind new. Let's see him say something that's actually correct.
 

Offline sorincosofret

  • Sr. Member
  • ****
  • Posts: 204
    • View Profile

A klystron works because of resonant cavities. A diode has none. Both exhibit the interaction between charges and em waves, one uses it to provide amplification and its design enhances this interaction, the other does not make a point of it. Do you not realise that electrical energy from the power supply (a flow of energy via an electric field) causes the acceleration of an electron. When it slams into the other end, the ke is transfered, via an elecromagnetic interaction as it collides with atoms, to internal energy.

The mechanism of klystron was described in another post with original explanation of inventor. The resonant cavity is used to catch a specific frequency. If a fascicle of accelerated electrons pass through such resonant cavity there is no microwave emission.
It is necessary to accelerate a part of fascicle and to decelerate another part in order to obtain microwave.
This can be tested very simple in every laboratory.
In the same time the kinetic energy received by anode in a small diode ( a simple math can be made) is so high that every diode should have a cooling device.
I have some old diode and other old tubes in my collection and they still work without this anode heating. Of course there is a general heat due to cathode system. But the anode temperature is lower then cathode.
« Last Edit: 04/11/2008 06:41:28 by sorincosofret »
 

lyner

  • Guest
Another one of your dodgy experiments, I think.
Did you put your finger on the Anode, then?
With 100V plate voltage and 10mA current, there would be 1W of dissipation - the filament supply would be several 100mA at 6.3 volts - a similar amount of heat dissipation.
Both would get hot. What does that prove for you?
Anodes of big thermionic valves do have heat sinks which glow 'cherry red'. What's new? So does the Collector of a power Klystron.
Do the 'simple math' you refer to and the sums come out just as you'd expect.
P = VI

If you could find the correct (English) terms for some words like 'fascicle' and 'comportment', it would make life easier  for all of us.

If you could explain how the RF energy from a Klystron comes out without including the acceleration of electrons and EM interactions I should be very impressed. It's all well understood and predicted by considering the very high oscillating fields across the gaps in the resonant cavities. It's a matter of ' matching' and resonance. Many cycles of cavity oscillations are required to interact with the bunched beam and the phase of the rf oscillation is critical. The effect of a single bunch of electrons would not be significant. Speeding up and slowing down are both 'accelerations'. The frequency of the photons in this interaction si the frequency of the resonant cavity. When the beam emerges, it is still bunched a bit and there is a more significant harmonic content than when it went in - the fundamental energy has been taken off.
Your superficial approach is flawed, as usual. Try reading some more about it and get informed. It takes more than skimming through an article to get a deep understanding. I spent months looking into this, some years ago.

« Last Edit: 04/11/2008 16:52:20 by sophiecentaur »
 

Offline sorincosofret

  • Sr. Member
  • ****
  • Posts: 204
    • View Profile
Again a lesson of elementary physics.
Using the up presented example let's calculate the temperature of electronic gas accelerated at 100 V, considering zero the initial speed of electrons emitted by cathode.
The acceleration of electrons in the tube is :
mv2/2 = eU
From actual kinetic theory of gases, there is
mv2/2 = 3kT/2
From the last two expressions there is:

eU = 3kT/2

1.6* 10exp(-19) * 100 = 3*1.38*10(exp-23)*T/2
 and then T = 0.77*10exp(6) K

In comparison with cathode temperature of maximum 1500K, the electron gas has a temperature greater then Sun surface (5000 K). At this temperature, which is transferred on anode after a short period of time the anode melts. In the construction of  diodes, usually, the anode is like a circular cylinder around cathode, so the entire heat  resulted from electrons smash is transformed in thermic energy.
In few days, actual theory predict the impossibility of diode working. In reality  such devices were used for long time and with satisfactory results.

The details about EM radiation will be included in the book...so there is no hurry.



 
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8644
  • Thanked: 42 times
    • View Profile
A very dilute electron gas with an effective temperature (not a real temperature BTW) near a million degrees will transfer about a Watt of heat the anode.
So What?
It's a bit like putting your finger through a candle flame- the rate of transfer of energy is quite low because a flame is pretty insubstantial.

If you use a higher power you can indeed heat things to very high temperatures.
This sort of thing uses it.
http://en.wikipedia.org/wiki/Electron_Beam_Melting
Once again Sorin is claiming something "new" that's really established technology.
 

lyner

  • Guest
Temperature is not what counts - it's POWER or rate of energy transfer. That's, as I said, VI. Any other argument is irrelevant and doesn't give you the right answer. (Another loophole in Science has been sealed up, sorin - it's not sinking)
 

Offline sorincosofret

  • Sr. Member
  • ****
  • Posts: 204
    • View Profile
If a small number of particle with high energy have the same effect like a greater number of particle with lower energy, only because the total energy is important ( and considering the same total energy), for me the discussion is closed. Let's leave this post to remain only as a historical proof that a strange mind had a strange idea. 
 

lyner

  • Guest
Let's just say that a strange mind tends to have pointless ideas.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8644
  • Thanked: 42 times
    • View Profile
How trustfully is the actual explanation of diode tube working?
« Reply #10 on: 05/11/2008 18:52:19 »
Let's rejoice in the fact that for once the strange mind has accepted it was a silly idea.
 

Offline sorincosofret

  • Sr. Member
  • ****
  • Posts: 204
    • View Profile
How trustfully is the actual explanation of diode tube working?
« Reply #11 on: 07/11/2008 05:13:10 »
It is not a silly idea; I don't have time to talk about nonsense.
 

lyner

  • Guest
How trustfully is the actual explanation of diode tube working?
« Reply #12 on: 07/11/2008 10:33:09 »
Quote
I don't have time to talk about nonsense.
Your posts suggest otherwise.
 

The Naked Scientists Forum

How trustfully is the actual explanation of diode tube working?
« Reply #12 on: 07/11/2008 10:33:09 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums