Current direction?

[gearhead]

I've got another one of those "Captain Obvious" questions, but it just has me puzzled. Been looking at the Express power/filter section

Running a current thru a resistor results in a positive voltage on the far side (where the current comes out). If this is the case, looking at the Express, the voltages out (B1, B2, etc.) can only result from the DC current running -from- the tubes/circuit into the power/filter section?

For example; B1 to B2 is a drop of 15V across the 1k resistor, or conversely an increase of 15V from B2 to B1. The current has to run from B2 to B1 for this to occur, and the filter caps to ground block the DC. The only other source can be the tubes/circuit.

Is this correct?

[VacuumVoodoo]

It's an ancient confusion between current flow defined as flowing from a point of higher potential to a lower potential and electrons moving in opposite direction. They flow from cathode to anode but the current flow is defined from plate to cathode. To avoid confusing your gray matter forget about electrons.

[stoo]

I think your getting electron flow and current flow confused..even though they are the same ...I guess
Current flows from the rectifier through the various resistors getting dropped along the way. If there was no current flowing the nodes b1, b2 ect would all have the same voltage. So you can say current is flowing from + to - . Now! If you look at a tube...The heaters boil electons off the cathode and the are attracted to the posatively charged anode (plate) in other words - to +.
I just realised I haven't answered you question . I think this is one of those things you shouldn't think about.... like infinity
Stew

[gearhead]

I had most of this years ago, and it's beginning to come back like a bad dream. Centuries ago some guy had to guess which way, and got it wrong.

When it comes to understanding tubes, current just doesn't work for me. Have got to go with electron flow, and will now have to reverse. That's where those "holes" come in, eh? LOL.

[Fischerman]

They flow from cathode to anode but the current flow is defined from plate to cathode. To avoid confusing your gray matter forget about electrons.

When it comes to understanding tubes, current just doesn't work for me. Have got to go with electron flow, and will now have to reverse.

This is the way it is for me too. When it comes to vacuum tubes and how they work...whenever I think in term of 'current'...it makes no sense at all (i.e. the grid is negative relative to the cathode and is physically closer to the plate...so why wouldn't all current from the plate flow to the largest and physically closest potential?). But when I think in terms of electron flow it all makes perfect sense (we now have an electron cloud around the cathode and it want's to flow to a high potential, i.e. the plate...but since the grid is negative and in between the two...it slows the electron flow).

[skyboltone]

Well maybe you should try to look at it another way. In the beginning there was dinosaurs and leafy plants..............power generation..........the origin of the juice that makes the noise comes from the wall plug.

Now, if voltage was being manufactured by the resistor between B1 and B2 there wouldn't be any utility company and no need for dinosaurs. Current flows from it's source to it's use (some form of work or heat). Voltage pushes that current. Current can be defined as great big bags of electrons passing a certain point. Measured in time as amps, measured in quantity as joules. The electrons boiling off the cathode (in a sense) began life as parts of carbon atoms in leafy plants. Don't think about falling water or wind power, it'll make things worse.

[juse]

http://www.allaboutcircuits.com/vol_1/chpt_1/7.html

[gearhead]

That's the quandry, exactly. Electron flow and current flow are opposite directions. I was using NEETs to brush up on some conventions, and wouldn't you know it, they are sticklers for electron flow:
"NOTE: In some electrical/electronic communities, the direction of current flow is recognized as being from positive to negative."

DOH. MY brain kept thinking positive to negative too, which is how I got wrapped around the proverbial axle.

Even though you stick with the current flow convention, to understand tubes and sources, electron flow is the way to go. For example, the electrons that run thru a cathode to the anode (whether thru a biasing resistor or not) come -from- the chassis and not to it. That's the source of one of the arguments of aluminum vs steel chassis; most of the electrons flowing in the circuit came out of the chassis from "ground".

It's amazing how much you forget if you don't use it. I used to understand and converse in electromagnetic field theory. Looks like greek now. Alright, so a lot of the symbols used -ARE- greek, but you know what I mean.

[BJF]

Hi,

You might aswell stick with what makes it easiest to understand. It's anyway just a model.
You'd sometimes see direction of current as defined from a higher potential to a lower, much because that's the way the pioneers of electricity saw it- makes more sense if you look at a lightning striking, while electronflow would be defined as from lower potential to higher as that is what the chemists later thought.
Nobody really knows which it really is, no more than anybody knows what the Sun consists of.
Once there was an attempt to replace electronflow with moving holes......... now the moving holes would go from high to low, which could sort of make sense with transistors and the chemical reaction inside but with electrontubes, many things, such as the basics are much easierly explained with electronflow like in the model that shows electrons as little balls enmanating from a pipe, the speed of the balls through the pipe showing the influence of heater supply, so that when in range the balls would pop off the end of the pipe onto a rubber cloth with rings to adjust the flow like the grids and the cloth end ring the anode.

However for the most part the direction of the current is of little consequence as long as the direction is followed consequently and usually the potential between two or more points might be the relevant information.

If you are looking at a B-tree check out the two laws of Kirshoff's, those will help you understand what's going on.
Since you most likely are going to work with the B-tree in static condition, like you want to set the voltage for each tap, then you can assume a current through one ECC83/12AX7 triode to about 1,6 mA.
The potentials you are then counting your way through at the taps will be the same regardless of the direction of current.



Have fun
BJ

[Jack]

Just to make matters worst, let me add that under normal circunstances, NO electrons actually go THROUGH a tube (same for a capacitor!). These electrons has to come from a solid contact. FYI.

[gearhead]

Yeah, you're right. For a wire (solid metal), it's more like a conga line, or dominos. For a capacitor, it's pure transfer based on em fields (that dielectric is -supposed- to slow/stop electrons).

However, for tubes, it is the flow of electrons from the heater-induced electron cloud around the heated-cathode.

[mhuss]

I beg to differ on the tube point. Unless electrons are moving (in the general/average sense), no DC current can flow. Therefore your idle current (that you measure, e.g., when setting bias) would always be zero!

Another way to look at it, a generic single stage amp (tube or transistor) is generally modeled as a fixed resistance (the load) in series with a variable resistance (the active element). This model won't work at all if DC does not flow. I think the principle at work in this model is why the Europeans call these "valves," i.e., "electron valves."

I always thought the way tubes/valves function is very intuitive as compared to the semiconductor physics, with the "holes" and "tunneling."

--mark

[Jack]

I beg to differ on the tube point. Unless electrons are moving (in the general/average sense), no DC current can flow. Therefore your idle current (that you measure, e.g., when setting bias) would always be zero!

Another way to look at it, a generic single stage amp (tube or transistor) is generally modeled as a fixed resistance (the load) in series with a variable resistance (the active element). This model won't work at all if DC does not flow. I think the principle at work in this model is why the Europeans call these "valves," i.e., "electron valves."

I always thought the way tubes/valves function is very intuitive as compared to the semiconductor physics, with the "holes" and "tunneling."

--mark

Which tube point do you not agree with? Mine or gearhead's?

In a semiconductor, the electrons actually flows through the device.

I tried to verify my claim about the tube but couldn't... I may be wrong but I'm fairly sure of my claim

[novosibir]

For a capacitor, it's pure transfer based on em fields (that dielectric is -supposed- to slow/stop electrons).

I'd rather say, that in a capacitor the foils are playing some kind of ping-pong with the electrons.

Larry

[novosibir]

However, for tubes, it is the flow of electrons from the heater-induced electron cloud around the heated-cathode.

And yes - in tubes there's definitely a electron flow from the cathode to the plate, which is literally absorbing the electrons.

But not only the plate, in fact all grids (control-, screen- & suppressor-grids) are more or less absorbing electrons too.

Larry