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8/26/2004 6:50 PM
anonymous BSSST
"The coupling cap question is easy to explain. Simply put, coupling caps react to both Pure AC and the Variable portion of Variable DC as well."
As KG used to say ... the bullshit detector just went off.  
You're outed on the first round dude - I thought you were gonna be a challenge.  
"Variable DC has an AC component to it that can be separated out by using a coupling cap. Basically it's the change in voltage that provides the coupling and not the reverse of DC current direction. DC current doesn't reverse direction."
That's just pathetic.  
You're sad dude, just sad.  
"And the AC portion of Varying DC can only be transfered across a coupling cap if there is a way to discharge the capacitor under conditions where the current doesn't reverse direction. This is because DC is not like AC and therefore doesn't automatically discharge the coupling cap by virtue of changing direction."
"The discharge mechanism is through current leaking out of the cap through the grid leak resistor on the grid side and through the plate resistor on the plate side. If the cap was not connected to these two resistors it could not discharge properly under a variable DC scenario and therefore would not couple."
You're really stretching out here.  
Go girl!  
[QUOTE]Now that I answered your not-so-silly question, please answer mine. How do you propose that AC is flowing through the coupling cap. What I want to know is where does the AC come from. If you are starting to buy into a portion of my variable DC theory then tell me how you see AC being derived from the varying DC. And if I still haven't convinced you of the existance of variable DC then tell me what is there that takes it's place.  
And I'll tell you what -- give me your explanation and I'll quit yanking your chain.[/QUOTE]  
Yank it some more dude - this is just good clean fun!
8/26/2004 7:20 PM
I couldn't help but notice that you disagreed with everything I said but provided absolutely no clarification why anything I said was wrong.  
And Yes you hit it right on the head. I am pathetic and my situation is very sad. In fact my whole life is a very sad state of affairs indeed.  
So why do you keep on writing back and conversing with me? Didn't your mother ever explain to you that you should avoid people like me? You know -- think back. It was probably right around the time she told you to never take candy from strangers. Mommy would not like you to take technical answers from strangers like me either. But then again, how elese would you learn how the world really worked.  
I'm still waiting for your explanation about that AC theory of yours. I'm all ears.
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8/26/2004 10:21 PM
Fine, here's the simple explanation:  
And here's a more comprehensive eplanation:  
Either way, capacitors block dc and pass ac.  
That's it, that's all, you're wrong, get over it.
8/27/2004 10:05 AM
DD My Final Post on this Topic
You are providing good references that I really don't disagree with. What I'm saying is that the variable DC component has AC properties to it that get passed through the coupling capacitor.  
And I'll let you in on a little secret. I've been wanking you. I have been wanking you not with lies but rather by using your own ignorance against you. I know that it's not nice to do this but so what. Shit happens.  
There is a minor flaw in my argument that I provided about how coupling caps work. I really thought you would catch it. In fact I encouraged you to catch it. I repeatedly asked you to tell me how pure AC gets generated in the circuit because in reality it is really there. But I have to sadly report that you just couldn't figure it out.  
So I'll be a nice guy and fill you in on the flaw. If you reread my explanation of coupling caps in a varying DC world you will note that I first talk about the coupling cap charging and then I talk about the cap discharging. All of this is true as I explained it. What you failed to note however is that the discharge phase of any capacitor requires current to reverse itself on the plates of the capacitor. And once the current reverses direction you have pure unadultreated AC across the capacitor. In sum, you have audio AC that truely does alternate directions through the coupling capacitor where the current direction reverses with every charge and subsequant discharge. But again, you have varying DC controlling this process.  
So in sum, as I correctly stated in my varying DC world analysis, the coupling cap is charged by variable DC and is not charged by pure AC. At the point of peak variable DC voltage, the cap is at maximum DC charge. As the varying DC voltage swings downwards, the cap has to discharge (i.e., reverse current direction) to equalize to the lower DC voltage. If you trace through the discharge path you will see that it involves both the path through the plate resistor as well as the path through the grid resistor.  
That's how it works. Basically amplifiers are varying DC devices that use coupling capacitors to convert varying DC into pure AC as described. For the most part the guts of the amp lives in a varying DC world. And for sure, it is varying DC that is directing the operation of a coupling capacitor.  
And by the way, none of what I said is inconsistent with the references you provided. Coupling caps simply convert the variable portion of varying DC into pure AC. But as the AC is sent to the next stage it gets combined immediately with grid bias and once again becomes varying DC.  
You can design good amplifiers by not knowing any of this. But you can design even better amplifiers by applying what I said. For example, the discharge paths are audio paths and therefore need to be kept to a minimum to minimize noise, hum pickup, as well as spurious oscillations. And how do you do this? By grounding the 1) the negative terminal of the PS filter cap, 2) the cathode bias resistor, the cathode bypass resistor, and 3) the grid leak resistor all to the same point on the grounding buss. You should do this separately for each stage. It is normal to think that the grid leak resitor is part of the circuit of the next preamp stage when in reality it is part of the first stage as described.  
If you choose not to believe any of this, I don't care. If you call on more experts and site more technical refences because you don't understand what I am saying, then I don't care either. As a famous philosopher once said "Ignorance is bliss." There is nothing wrong with being blissful and happy in life. If you wish to be happy in life, site more experts. If you want to be a little less happy, then take the time to read what your experts have said and I will pretty much gaurantee you that they support what I have said.
8/27/2004 1:54 PM
Please go away.
8/27/2004 2:05 PM
DD, just ignore these guys. Your explanation makes sense to me. Don't waste you're time with people with limited minds. There are more important things to do in life.
8/28/2004 9:45 AM
Now was that the explanation about directional wire or ac that's really dc - you now that kind of dc that fools your scope and displays as ac (but really is just dc in diguise?
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