Rk vs Rg voltage

[EtherealWidow]

But see, although they're "separate" currents, since this is a circuit, all of these currents intermingle and mix eventually. I mean, there's current coming from the guitar, rectifier, preamp tubes, and power tubes. Although these all start out as separate currents, they intermingle and influence one another and eventually all come back to the same source, the rectifier cathode, then go to the anode, then to ground where it all starts over again. When designing these and analyzing them, they can be broken down and treated as separate circuits, but they're all interrelated.

In my view, which might be wrong as I seem to be contradicting almost everyone on TAG Both Rg and Rk are connected to a current source; Ground, which is the anode of the rectifier. The only difference is that Rk has another current source on the other end of it as well.

[Tillydog]

... each tube is a current source.

Nooooo...

The only place current comes from is the power supply, and that's also where it's got to get back to - like water in a heating system comes from the pump and needs to get back to the pump.

You need to get your head around that concept to understand any further....

Have a look at these, particularly the second one:

http://vimeo.com/28166314

http://vimeo.com/28565075

http://vimeo.com/33244955

Edit to add:

This one, too - it's a java applet. You can click on the switches to change the configuration of the circuit. The grid behaves the same as an open switch....

http://www.falstad.com/circuit/e-resistors.html

[EtherealWidow]

So you mean to tell me that although the cathodes are boiling off their own separate electrons, they're not sources of current?

[Tillydog]

So you mean to tell me that although the cathodes are boiling off their own separate electrons, they're not sources of current?

Correct!

The cathode is just a way of getting the electrons out of the wire and into the vacuum - the electrons (or their replacements) are coming from the power supply.

[tubeswell]

The boiling off merely represents the process of exciting the electrons to a higher state of kinetic energy than they would otherwise be in if the cathode wasn't heated. They are sufficiently 'freed' from their atomic orbits to be enticed to 'flow'. The 'boiling off' aspect is not the tube current 'flowing' per-se, rather it is one of the preconditions to getting tube current to 'flow'. But it is critical because this energising makes the job of the plate (to pull electrons across the gap between the cathode and the plate) easier. There is no equivalent to this heat catalyst at the grid.

[EtherealWidow]

Oh wow. Well, you've all been wonderfully patient with me. Hope this is a help to someone else as well. Thank you. I have to read this entire thread all over again now. So, not to beat this dead horse or anything, but even though new electrons are being introduced from each tube's cathode, they're not considered sources of current? I understand all the other basic functions of the triode, just figured they were ADDING to the total circuit current.

[tubeswell]

Current needs voltage to 'flow' across resistance. So heating up the cathode is not sufficient on its own to create the condition of tube current. As I said earlier, the heating is one of the pre-conditions. The other pre-conditions are plate resistance and plate voltage.

[Firestorm]

So, not to beat this dead horse or anything, but even though new electrons are being introduced from each tube's cathode, they're not considered sources of current?

There are no "new" electrons; all the electrons that exist in the universe are all the electrons that are ever going to exist. All we can do is move them from one place to another. Conductors do not hold onto their valence electrons very well, so they easily pass them on atom to atom, but they will always want to replace the ones they give up. Diodes let us force this exchange in one direction only; then, by using resistances, we can slow down this process of replacement to create different potentials between circuit elements.

[EtherealWidow]

Alright. I get it now. I think a lot of the misunderstanding came from the fact that since the space charge is technically introducing "new" electrons (electrons that wouldn't be there if the tube weren't present) it doesn't necessarily mean that it's adding current to a circuit, it's just manipulating it. In the same way that adding any conductor like say, 18awg wire is technically introducing "new" electrons, but not adding current. Sorry guys. Hope this helps someone else and not just me.

[vibratoking]

Alright. I get it now. I think a lot of the misunderstanding came from the fact that since the space charge is technically introducing "new" electrons (electrons that wouldn't be there if the tube weren't present) it doesn't necessarily mean that it's adding current to a circuit, it's just manipulating it. In the same way that adding any conductor like say, 18awg wire is technically introducing "new" electrons, but not adding current. Sorry guys. Hope this helps someone else and not just me.

I am glad to see your understanding is getting better. Your perseverance is being rewarded. I know I enjoy learning new things. Manipulation of the current is what the vacuum tube is all about. It's very interesting to note that small VOLTAGE changes at the grid result in large CURRENT changes between the plate and cathode. Transconductance is the essence of vacuum tubes and FETs.

[EtherealWidow]

Sweet. Well thanks again everyone for all your input and knowledge.