Looking for an online tutor

Discussion in 'Homework Help' started by Amps71, May 26, 2015.

  1. Amps71

    Thread Starter New Member

    May 26, 2015
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    Hello

    I am looking for some help in understanding some basic electronics circuits and terminology.

    I am not adverse to paying for the help (paypal) - I need someone I can banter with via email. I am reading a lot of books and I am not getting the feedback I need to go forward.

    I appreciate the help!

    T
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Post your questions here. We do a lot of tutoring for free...
     
    panic mode likes this.
  3. tshuck

    Well-Known Member

    Oct 18, 2012
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    Hi T,

    While I don't have a solution to your tutor problem, forums such as these are a great resource to get answers to specific questions you may have.

    I'd suggest you start a new thread on a topic you'd like clarification on.
     
  4. Amps71

    Thread Starter New Member

    May 26, 2015
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    Ok, sounds good!

    The items, specifically I cant seem to get my head around are quite basic:

    1. I dont understand "shunting to ground".
    2. I understand the IDEA of capacitors and how they work, I cant get my head around how they work with a voltage, inasmuch as by-passing or coupling. Or generally how they work. I know in theory how they work but cannot put it into practice.
    3. I just cannot understand schematics. Like the one attached. Very confusing to me.
    4. I am having serious issue with capacitive reactance.

    Basically this all stems down to how a tube amplifier works - which I find interesting (im grabbing the concept of how the signal gets through the valve easy enough). But I am confused on how the anode retains a positive charge.

    I know this is all fairly basic but I'm not getting that "lightbulb" moment I thought I'd get by now. Thats sorta why I was looking for a tutor - to bandy silly questions back and forth.
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    Point #3 suggests an attached schematic, but it seems to be missing.
    As a component, a capacitor is just a pair of parallel conductors. An ideal capacitor presents an infinite resistance to the flow of DC current. So right off the top there is the first appication of a capacitor in a tube amplifier. It BLOCKS the flow of DC current and is even called a "blocking capacitor", for that reason. Next thing to consider is what happens if the voltage across a real capacitor is increased without any practical limit. The answer is that at some high voltage, there will be a spark between the plates and a momentary DC current will flow until the spark can no longer be maintained.

    In an AC circuit we have a situation where the conductors are charged and discharged in opposite directions on each half cycle. The faster this process goes the less resistance to the flow of AC current there is. So a capacitor to GROUND looks like an OPEN circuit at DC and a SHORT Circuit at high frequency, and something in between at intermediate frequencies. In this application, called bypassing, we want high frequency noise to be "shunted to GROUND". It means the same thing as reducing the noise in a circuit by providing a low impedance path to ground for high frequency signals.

    So does this trigger some additional questions?
    How about an animation.
     
  6. DickCappels

    Moderator

    Aug 21, 2008
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    @Amps71, There is no schematic attached to your post.
     
  7. Amps71

    Thread Starter New Member

    May 26, 2015
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    Thank you for your help! And here is the file. In the PDF, I understand the inputs, where the tubes are...what I don’t understand is the ground symbols – where do they go to? As I mentioned, if I could see a schematic like this in an actual circuit it would make a world of difference. As well, the lower right hand side, the two 8-450 capacitors. I don’t understand how the power supply goes by them and then goes to the caps and then to ground? And what does the 500 ohm resistor do?

    Is there a program where I could plot out the schematic on my PC and view it? Papabravo, your video was great - If I could see this schematic in a video like that it would make worlds of difference.

    T
     
  8. DickCappels

    Moderator

    Aug 21, 2008
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    First the easy one, the ground symbol. Three commonly used ground symbols are shown below[​IMG]
    Everything that connects to a given ground symbol is connected to everything else shown connected to that symbol. The symbol does not say anything about the spatial relationships among the contact points. One common ground connection is a ground plane on a printed circuit board. In the old days (not that long ago) the many component used the metallic chassis as a ground connection for some parts of the circuitry.
     
  9. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The ground symbols in that schematic are electrical short-hand for "connect this to the metal chassis". The metal chassis is like a fat wire. All of the ground symbols are connected together electrically (at the same voltage).

    btw-the way that amp is wired does not meet modern AC wiring standards, is a safety hazard, and will introduce hum into the audio. It is really a poor design...
     
    Last edited: May 27, 2015
  10. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hello there,

    There are two general forms of analysis and DC analysis:
    1. Time domain
    2. Frequency domain
    3. DC analysis

    I mention this because when you go to solve a problem you first want to know what kind of method you are going to use which also gives you a certain kind of result.

    For example, to figure out how a capacitor charges you work in the time domain, but to figure out the capacitive reactance you work in the frequency domain. To solve a resistor network with say some batteries you do a DC analysis, for example.

    Each one of these categories has it's own set of procedures that work well for finding out the kind of answers you want, and the kind of math background you need for each category is different, although some types of math will be used for all three such as Algebra.

    The way you normally start to study these is by starting with DC analysis. Solving networks of resistors with voltages sources like batteries. You solve for the DC current and DC voltage in various places in the network, and you'll need a working knowledge of algebra.
    Once you master this, you then move on to AC analysis, which is really frequency domain analysis. You can get pretty far with this just knowing algebra and complex algebra.

    Saving the time domain analysis for last, you want to know some calculus and differential equations. There are various techniques here, and that includes converting from the time domain to the frequency domain and also vice versa.

    So my suggestion would be to start with DC circuit analysis, and once you have mastered that move on to AC analysis, then to the time domain analysis.

    Also, unless you have a specific need to study tubes you are probably better off going with bipolar transistors to start.

    Example of a reactance, in rectangular form:
    X=3.4+7.26*j

    Example of a time domain analysis result:
    V(t)=Vs*e^(-t/RC)

    Example of a frequency domain analysis result:
    V(s)=E(s)/(s*R*C+1)

    Example of a simple AC analysis result:
    Vac=120vrms at an angle of 90 degrees
     
  11. Amps71

    Thread Starter New Member

    May 26, 2015
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    Thanks for the quick answers everyone. With regard to the ground chassis - would all grounds be connected to the same spot or different parts of the chassis? Is there a common "wire" they all attach to and then one wire to chassis? For example, if I took the schematic and drew a thread through all ground icons and "attach" that thread to ground on the chassis, would that be correct?

    Mr Al - I seem to have a good grasp on DC, OHMs law, KCL, KVL, voltage dividing, series, parallel, etc. Its the move to AC thats sort of bending my head a bit. I can do algebra and calculus. I may be over analyzing it all a wee bit as well and that may be causing my confusion. I've been known to get in my own way before.
     
  12. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Different spots, disjoint, locally connected, wherever mechanically convenient, spread all over the chassis. Good example is your automobile. The car's frame and chassis is used as the return path for every appliance in the car. For example, the headlamp socket is attached to the frame near the headlamp; there is not a separate wire running all the way back to the negative pole of the battery.

    That style of wiring would be referred to as "single point ground". It has a use in certain circuits, but not in the schematic you posted.
     
  13. Amps71

    Thread Starter New Member

    May 26, 2015
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    And to avoid shock from the chassis, how is that avoided? If the ground points are all connected to chassis, the chassis, I assume, becomes part of the circuit, correct?
     
  14. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I refer you to the last sentence in post #9.
     
  15. Amps71

    Thread Starter New Member

    May 26, 2015
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    Thanks MikeML. I think it is a quite old schematic. I will google ground wiring for electronics.
     
  16. bertus

    Administrator

    Apr 5, 2008
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