Electron path of travel

[trem]

I hate to be the one that always asks these rudimentary questions, but that is my level of knowledge.....
Just to make things easy, lets assume we have a 12AX7 triode. I thought the flow was from the cat resistor, past the cathode, the grid and onto the plate. I am not sure where the current goes after the plate.
In Merlin's book, last paragraph of page 17, he talks about biasing. To paraphrase...."current flows through the valve, out of the cat, and down through the cat resistor.
Have I misunderstood the current through a tube, or are there two directions of electron flow somehow...? I always read about electrons leaving the cat, controlled by the grid, "slamming into the plate, bouncing off, and that is why the suppressor grid was developed.
Can you guys tell me the basic path of travel that electrons take in a tube..?
Thank You Very Much

[tubeswell]

Free electrons flow - as you say - from a more-negatively charged particle to a more-positively charged particle all other things being equal. 'Conventional current' flows in the opposite direction - from positive to negative, because that was how it was originally theorised at the dawn of electricity (and it has stayed that way because its 'conventional'). Think of it as the direction that the holes left behind by the departing electrons (which are 'flowing' the other way) flows in. That's my take on it anyhow

[mooreamps]

I hate to be the one that always asks these rudimentary questions, but that is my level of knowledge.....
Just to make things easy, lets assume we have a 12AX7 triode. I thought the flow was from the cat resistor, past the cathode, the grid and onto the plate. I am not sure where the current goes after the plate.
In Merlin's book, last paragraph of page 17, he talks about biasing. To paraphrase...."current flows through the valve, out of the cat, and down through the cat resistor.

Really ? Perhaps his book is more screwed up than I thought... The "free electrons", after striking the plate return to the positive side of the high voltage power supply..

-g

[imaradiostar]

This is a long running discussion- electron versus conventional electron flow, as Tubeswell said! Think of it however you need to in order to grasp it. You can google it and read for a long time if you choose to!!

I prefer to think of cathodes emitting electrons or particles or somesuch thing so I favor that school of thought. There are historical experiments (gold foil experiment, for example) that lend credence to the idea that a heated cathode emits something. I find it easier to think about things that way.

jamie

[Chuck H]

+1
For our purposes... The cathode (which is biased negative in relation to the grid and plate) is heated and this excites electrons and free's them. These electrons are eminently attracted to the VERY positive plate. The grid acts as a valve to control the flow of electrons from the cathode to the plate. Small vriations at the grid control this electron flow and the comparably high amount of electrons from the cathode gated (by the grid) to the very high voltage of the plate creates a mirror (but in greater proportion) of the grid input at the high voltage plate. As far as I'm concearned any electrons flowing the other way are incidental to the function at hand since they aren't heard and I niether have enough tech training or problems with the phenomenon to bother considerint them.

[guitarmike2107]

simply put, electrons flow from negative to positive. conventional current flows from positive to negative.

note they are not the same terms.

so yes the electrons move from the cathode to the plate.
but conventional current flows from the plate to the cathode... confused yet

[Chuck H]

yes

[Enzo]

The physics of the tube are based upon electron flow. Electrons - your current - flow from the hot cathode to the plate, through the plate load and into the power supply. The other end of the power supply replenishes the electrons the cathode gave up through the cathode resistor. This is how tubes work, no one questions it. Look up "space charge" and go from there.

SO in a sense, ground is the source of all your electrons. The B+ is a big electron vacuum sucking for electrons, which come up through all the cathodes to satisfy its appetite. There is only one direction of electron flow. At least in the sense you discuss. The power supply is a big electron vacuum pump creating an electron vacuum in the B+ nodes, and of course pressurising ground with lots of electrons.


Now there is also this concept of "Conventional Current", which I think of as more an old school relic. I myself am an old school guy, so I don;t mean that unkindly. COnventional current does flow the other way, except nothing is really flowing other than the concept. I think Tubeswell is right, that it came from old theories, but others are better versed in the history of the technology than I.


By the way, holes don;t move the opposite way. Look at the chase lights around a movie marquee, you see the lights all moving one direction, The dark bulbs - the holes - do not appear to move the other direction. This is analogous.

I think in conventional current, all the while being totally aware that electrons are actually flowing the other direction. In a sense it really doesn;t matter. Think about it. Your tube has X current flowing through it. The plate has Y volts on it and the cathode Z volts. The grid has C volts on it controlling the current through the tube. What difference does it make which direction the actual electrons are moving to the concept? I never see them. Kinda in the sense of AC current - does it really matter at any given instant, which way the AC current is flowing in your power cord? Oh it matter that two sources of AC have the proper phase relation if they are combined, but that is not the same thing.

Ground is the master reference point for most of what we do. SO conceptually it is maybe easier to think of that +450VDC B+ as a source of something trying to find its way to ground, like a community water tank full of water, whose pressure from gravity then feeds all the town faucets. But in reality it is the opposite. Imagine you have a vacuum tube, and you crack the glass. Well we just let the air into the tube. But it could be just as convenient to think of it as having let the vacuum OUT of the tube. That is not the case, but if it made things simpler to visualize, then we might describe it that way.


OK OK, I gues the whole atmosphere of the earth now has a tiny bit more room - the room inside the cracked tube - and so the overall pressure of the atmosphere is thus reduced by some tiny amount, but no one could measure that...


Merlin knows how tubes work. perhaps using conventional current terminology is confusing, but if used consistently, you get consistent results. He didn;t say electrons flow down the cathode resistor to ground, he called it current.

If you understand how a tube functions, then it is jarring to use conventional current when you encounter the tube itself. I agree

Electron flow is how things work, conventional current is only a concept, a way to think about circuits.

Think for a moment about "signal path." We might look at an amp and think the signal comes in here, flows through that grid and out the plate of V1 over to the grid of V2, where it is further amplified and comes out the plate of V2... Well, nothing flowed from grid of V1 to plate of V1, other than the information in the signal. There was no current flowing there. There is no connection between the input of an amp and its output, yet we describe signal as flowing through it. it is a useful convention to describe it that way.

[Jazz P Bass]

I have always liked the phrase "Lost It's Vacuum"
How do you lose a lack of something?
Kind of like reverse entropy.

[jrfrond]

Enzo's description is brilliant and spot-on. I was going to write something along the same lines. There's only one practical point I'd like to add: because ground is the source "pool" of electrons (I sometimes use the description of a pool and the filter) is exactly WHY grounding is so critical. It's not just some crummy return line to the chassis and/or power supply. It is essentially the whole ball of wax, and poorly-designed or implemented grounding and ruin a good design. Without a good "pipeline" for electrons (and it IS ELECTRONics we are discussing), your system may not work at all.

The physics of the tube are based upon electron flow. Electrons - your current - flow from the hot cathode to the plate, through the plate load and into the power supply. The other end of the power supply replenishes the electrons the cathode gave up through the cathode resistor. This is how tubes work, no one questions it. Look up "space charge" and go from there.

SO in a sense, ground is the source of all your electrons. The B+ is a big electron vacuum sucking for electrons, which come up through all the cathodes to satisfy its appetite. There is only one direction of electron flow. At least in the sense you discuss. The power supply is a big electron vacuum pump creating an electron vacuum in the B+ nodes, and of course pressurising ground with lots of electrons.


Now there is also this concept of "Conventional Current", which I think of as more an old school relic. I myself am an old school guy, so I don;t mean that unkindly. COnventional current does flow the other way, except nothing is really flowing other than the concept. I think Tubeswell is right, that it came from old theories, but others are better versed in the history of the technology than I.


By the way, holes don;t move the opposite way. Look at the chase lights around a movie marquee, you see the lights all moving one direction, The dark bulbs - the holes - do not appear to move the other direction. This is analogous.

I think in conventional current, all the while being totally aware that electrons are actually flowing the other direction. In a sense it really doesn;t matter. Think about it. Your tube has X current flowing through it. The plate has Y volts on it and the cathode Z volts. The grid has C volts on it controlling the current through the tube. What difference does it make which direction the actual electrons are moving to the concept? I never see them. Kinda in the sense of AC current - does it really matter at any given instant, which way the AC current is flowing in your power cord? Oh it matter that two sources of AC have the proper phase relation if they are combined, but that is not the same thing.

Ground is the master reference point for most of what we do. SO conceptually it is maybe easier to think of that +450VDC B+ as a source of something trying to find its way to ground, like a community water tank full of water, whose pressure from gravity then feeds all the town faucets. But in reality it is the opposite. Imagine you have a vacuum tube, and you crack the glass. Well we just let the air into the tube. But it could be just as convenient to think of it as having let the vacuum OUT of the tube. That is not the case, but if it made things simpler to visualize, then we might describe it that way.


OK OK, I gues the whole atmosphere of the earth now has a tiny bit more room - the room inside the cracked tube - and so the overall pressure of the atmosphere is thus reduced by some tiny amount, but no one could measure that...


Merlin knows how tubes work. perhaps using conventional current terminology is confusing, but if used consistently, you get consistent results. He didn;t say electrons flow down the cathode resistor to ground, he called it current.

If you understand how a tube functions, then it is jarring to use conventional current when you encounter the tube itself. I agree

Electron flow is how things work, conventional current is only a concept, a way to think about circuits.

Think for a moment about "signal path." We might look at an amp and think the signal comes in here, flows through that grid and out the plate of V1 over to the grid of V2, where it is further amplified and comes out the plate of V2... Well, nothing flowed from grid of V1 to plate of V1, other than the information in the signal. There was no current flowing there. There is no connection between the input of an amp and its output, yet we describe signal as flowing through it. it is a useful convention to describe it that way.

[R.G.]

By the way, holes don;t move the opposite way.

This is actually a bit of a problem.

I was extruded through a semiconductor physics class at a couple of points in my education. Both electrons and holes are current carriers in semiconductors. It's a bit of a story, but if you're interested, here is is.

A pure silicon crystal has every single atom being electrically neutral. If you force in different atoms into the crystal, the incoming dopant atoms are still electrically neutral, in that they all have the right number of electrons to offset the number of protons in their nucleus. But forcing them into the crystal replaces a silicon atom with an atom that has one more or one less than the number of electrons in the atoms of silicon around it. If it has one more electron than the surrounding silicons, it's an N-type dopant; if it has one less, it's a P-type dopant.

What this does is to force a place in the crystal that has an extra (or missing) electron compared to the crystal around it. Although the whole mess is still electrically neutral when averaged over the whole thing, same number of protons and electrons, there is either a net extra or net deficit of an electron at the dopant position. This extra/missing electron is what lets the silicon conduct, as the non-uniformity of the charge distribution manifests itself as making it easier for electrons to move around.

Sorry - I'm getting there. I'll hurry.

If you put an N-type material against a P-type material, there is a place where they join that has excess electrons on one side and excess holes on the other: yep, they cross over to neutralize the average charge, and you get a junction that conducts better when you tell it to go the way it wants to instead of the way it doesn't. It's a diode. However, forcing currents through it in a bipolar junction causes BOTH the movement of electrons one way and holes the other.

It seems like pure sophistry to say that electrons, and holes, which are the net absence of electrons, are different, yes?

However, I remember being thunderstruck the day when our prof pointed out that you can measure both electron mobility in a silicon lattice and hole mobility in a silicon lattice AND THEY'RE DIFFERENT. The energy needed to move a hole leftwards is NOT the same as the energy needed to move an electron rightwards. Measurably different.

Holes have a different mobility than electrons, and this accounts for much of the difficulty in making good NPN germanium transistors and good PNP silicon transistors, as well as the difficulty in making good complementary types in either family. You have to get very sophisticated to get the opposing types to be equal in properties.

I think in conventional current, all the while being totally aware that electrons are actually flowing the other direction. In a sense it really doesn;t matter.

At the macro level, it does not matter. Historically, folks educated in the formal electronics disciplines were taught conventional current flow up through the 60s, and then were forced into learning both conventional and electron flow as semiconductors came to dominate; folks educated in military tech training were usually taught only electron flow, at least back into the 70s or so. Maybe they're taught both today. I know the guys in EE class with a military tech background had horrible difficulties with conventional current flow.

The equations work out the same at most levels where the actual movement of single electrons are not at issue. This matters in the fine structure of semiconductors and electron tubes - and especially CRTs, where electron ballistics are a big deal - but not at all once you get outside the functioning of the device internals.

[tubeswell]

By the way, holes don;t move the opposite way.

What I probably should have said was if I have dug a hole and then I fill it up from stuff I got from digging another hole next to it, it would appear as if the hole moved the opposite way to the stuff I chucked into the first hole. I have learnt this the hard way from diggin' many holes fer myself

[Merlinb]

Additional confusion arises because engineers usually talk about current flowing from A to B, which makes it sound like current is the thing that is moving. However, strictly speaking, current does not move at all, it simply exists (or doesn't exist). Saying that current flows from A to B is just casual speech, and it is more correct to say "the current in a wire", rather than the "current flowing in a wire".

Remember, a river has a current. But it is the river that flows, not the current. Similarly, a lot of people can run in a marathon, but it is the people that move, not the marathon. The marathon simply exists as long as the people run. It is the same with electric current.

Furthermore, current is the first derivative of charge with respect to time. Electrons, movement and direction don't come into it. The notion of a direction of current is meaningless; gibberish in fact!

It must also be pointed out that electrons are not convenient little particles with a definite direction, they are simply arbitrary models of something we can measure but can never understand. Electrons are not particles, and neither are they waves; they are something in between. And the fact that they carry a negative charge rather than a positive one, and that the sign of electric current is defined with respect to positive charge, was all arbitrarily decided donkey's years ago. In other words, "electron current" is in no way "correct", and conventional current is in no way wrong.

Electrons are not particles, charge is a property and not a thing, electrons have nothing to do with the definition of current, current does not move in a direction; it simply exists!

[mooreamps]

Really. Electrons are not particles ? Have nothing to do with the definition of current ? Not even inside Edison's Light Bulb ? You ever think about getting into some "other line of work"?

INTRODUCTION TO ELECTRON TUBES

-g

[R.G.]

You ever think about getting into some "other line of work"?

Ever think about not being so snotty any time Merlin makes a post? It's completely uncalled for.

Electrons are both particles and waves at the same time. Wanna discuss the technicalities? 8-)