Ground misunderstanding

Discussion in 'General Electronics Chat' started by Toddstar71, Apr 23, 2015.

  1. Toddstar71

    Thread Starter New Member

    Apr 23, 2015
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    Hi everyone - I'm new to electronics and I cant understand for the life of me how electrical ground works in a circuit. I'm learning about vacuum tubes. I understand that the cathode boils off electrodes to the plate. Got it. But when I see a schematic it shows a resistor or a capacitor connected to ground completely in the opposite direction of how the current flows from cathode to plate. Maybe I can't understand circuits. If current flows from ground through the cap or resistor how can it "get" to the cathode? Its very confusing. Any help is appreciated!

    TS
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    A diagram of what you are talking about would be very helpful in keeping the discussion on the same page.
     
  3. Toddstar71

    Thread Starter New Member

    Apr 23, 2015
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  4. MaxHeadRoom

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    Show an example!
    Also the flow from cathode to anode is the electron flow, but the flow is usually refered to in the opposite direction called the conventional flow. Due to a historical mistake.
    Max.
     
  5. Toddstar71

    Thread Starter New Member

    Apr 23, 2015
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    There you go. It confuses the heckbout of me. And I know its so basic.
     
  6. #12

    Expert

    Nov 30, 2010
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    First, all those ground symbols are connected together. Second, the cathode doesn't make electrons. The cathode gets the electrons from the ground symbol and allows them to be sucked up through the tube to the other (positive) end of the power supply voltage.

    Does that cover the first misconception?

    The electrons get from the cathode resistor to the cathode through a wire.
     
  7. Toddstar71

    Thread Starter New Member

    Apr 23, 2015
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    It does, yes. At the beginning, where the input transformer is, the .05/600 cap from ground. How does that "affect" the power from the wall to the transformer?
     
  8. MaxHeadRoom

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    There are two examples of a capacitor used in the circuit, one is connected to the tube grid and allows for the AC part of the signal to flow, while blocking AC, the other from cathode to ground across the cathode resistor is called a de-coupling capacitor, and essentially, references the cathode to ground as far as the (AC) signal is concerned, but allows the cathode resistor to bias the cathode above ground as far as DC is concerned.
    Max.
     
  9. #12

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    The 0.05 @600V cap is a horrible mistake by Leo Fender. It allows one side of the power cord to apply voltage to the chassis if you plug it in upside down. That is how singers get knocked unconscious when they, "kiss the mic".

    Well, at least knocked silly.
    That was before the 3 wire outlets were standard.
    Some attempt to allow the chassis to be at the same AC potential as the Neutral power wire. A half baked idea in my opinion.
     
    Last edited: Apr 23, 2015
  10. Toddstar71

    Thread Starter New Member

    Apr 23, 2015
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    You guys know your stuff! Thanks! On the B+ line from the input transformer as the line 90 degrees up, there is a cap then 500 resistor then cap on that are connected to ground. How is the wire voltage changed by the caps if it appears the voltage doesnt go through them..it appears as if they are drawing from ground? Maybe I'm confused by schematics. Any advice?
     
  11. #12

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    Yes, we do. :D
    I played guitar with one of Leo's shop technicians. :cool:

    Anyway, the capacitors are there to let the AC content of the rectified voltage pass through the ground symbol, back to the transformer. They don't change the DC, they just clean it up. The reason the cleaning is done in (2) sections is that it is more effective per dollar than trying to do it in one capacitor.

    You need to learn that the AC and DC components are in an intricate interplay all through this design.
     
    Last edited: Apr 23, 2015
  12. MaxHeadRoom

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    Unfortunately the circuit you posted has many anomalies that you will have to learn to overcome, due to mistakes often made by those that originate schematics such as this, the example amplifier shows a mains powered system that most likely is derived from a supply that is referenced to earth ground, i.e. one side of the supply will at some point in the supply origin is connected to earth ground, and the capacitor 600v .05uf cap is typically an attempt at suppression on the AC supply as it is connected to the live terminal to earth ground.
    This is where the confusion comes in, the galvanically isolated supply via the transformer, also shows the supply common connected to earth ground via the applicable Earth ground symbol.
    Now whether the originator of the circuit intended for the common to be connected to earth ground is a moot point.
    We will have to assume that it is, but because the circuit originator may have been guilty of using the earth ground symbol by default makes it up in the air.
    Unfortunately you will find that you will have to decifer circuits like this due to the sloppy use of official symbols.
    Max.
     
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  13. MaxHeadRoom

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    BTW another mistake is using the power switch in one line and the system fuse in the other.
    Max.
     
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  14. #12

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    In some of the Fender designs, there was a, "ground" switch that connected the capacitor to one side of the power cord, or the other. Still a half-baked idea! I spent many an evening synchronizing ground switches so the musicians didn't get shocked. :mad:

    Here's one with the, "ground" switch.
     
  15. Toddstar71

    Thread Starter New Member

    Apr 23, 2015
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    Really appreciate all the help! In your opinions, how do I understand these circuits? Its the idea of the b+ line and those caps from ground. Is the current coming from ground? Or is the ht going past them?
     
  16. Toddstar71

    Thread Starter New Member

    Apr 23, 2015
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    I guess what I mean is in the schematic it doesnt appear the b+ line is actually being filtered by the caps from ground. It appears b+ goes right by it.
     
  17. MaxHeadRoom

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    You need to study how a capacitor operates in relation to AC and DC, the b+ capacitors act to smooth the DC ripple as well as decouple the supply as far as AC is concerned, i.e. make the +ve & -ve identical as far as AC is concerned.
    Max.
     
  18. Toddstar71

    Thread Starter New Member

    Apr 23, 2015
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    So on the schematic, the b+ goes through the caps that have the grounds on the other end of them? Its just how the schematic is designed? I understand how the cap works - what I can't figure out is how the schematic works.
     
  19. #12

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    This can be a very long discussion. Google "How does a filter capacitor work".

    Picture the filter capacitors as coffee cans. The transformer/rectifier sucks electrons out of the capacitors in pulses according to the power line frequency. The capacitors charge up toward several hundred volts of DC. Meanwhile, the amplifier keeps using up some of the power...leaking electrons into the coffee cans. This makes the DC voltage wobble in between charging pulses. If the capacitors weren't there, the DC voltage would be ALL wobble! The capacitors store energy between power line pulses and feed the amplifier until the next power line pulse arrives.

    So, yeah, in a way, the B+ goes right by the capacitors. They are busy storing charge and releasing it as needed so the B+ doesn't collapse 120 times per second.
     
  20. Toddstar71

    Thread Starter New Member

    Apr 23, 2015
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    OK! Now I'm kinda getting it! Awesome!!!!
     
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