Diagram

Discussion in 'General Electronics Chat' started by chow_dairy, Mar 26, 2014.

  1. chow_dairy

    Thread Starter New Member

    Mar 26, 2014
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    I am trying to decipher this circuit diagram here: http://tuopeek.com/lissajous.html

    So far, I've been able to figure out that on the left are two signal generators, both connected to amplifiers and then to air cores. My question is: how do the air cores connect with the main circuit? And what exactly are air cores?

    On the bottom are three SPST switches, all grounded. And there is a 'Heater'; possibly a volt heater? And what exactly are those?

    And at the top right there is an EHT transformer. But there are two rectangles with arrows pointing through them that I cannot figure out.

    Any help is appreciated.

    Thanks,
    chow_dairy
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The Lissajous figures are by diplaying the X axis signal relative to the Y axis signal, hence the two inputs on the RH side shown at 90° to one another, air cores are inductors with no material ,ferrite, iron etc used in the core.
    As shown, these are external scan coils on the neck of the tube or crt.
    The heaters are shown as for three cathode emitters, this would only apply if a colour crt was used, red,green,blue guns.
    The EHT unit, Extra High Voltage supplies the voltage for the focus and brilliance grids for the CRT as well as the final anode voltage .
    Max.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Its a CRT, you need the heater to emit electrons these are attracted by the high voltage anode, usually 10 to 20Kvolts, as for the arrows they are variable voltages for focus, and brightness.

    see CRT
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    BTW if this is just a modification to a TV to display Lissajous figures, you don't necessarily need a colour CRT, a B&W will work for simple unicolour display.
    Max.
     
  5. chow_dairy

    Thread Starter New Member

    Mar 26, 2014
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    0
    Thanks for the replies. This is my first time understanding a circuit diagram concerning CRTs, not really sure what comes with the CRT and what is added for just this experiment. Do the air cores usually come with a CRT in an average color TV?

    Did you mean the left hand side? I'm having trouble identifying the inputs. Are there symbols on the actual lamp that I am missing?

    Would it be safe to assume that this would be a place for potentiometers (among other places in the diagram)?

    Thanks for the help so far, I think the best course of action right now is to open this sucker up and start tinkering (with respect to safety of course).
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That should have read LH side! The coils shown are X & Y (Horiz & Vert) deflection coils mounted around the neck of the tube or CRT, right up against where the CRT bell starts to flare in shape.
    Max.
     
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  7. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the diagram is a little ambigous because its a generic tv diagram. showing how but not exactly how to modify a tv to act likie an osciloscope.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Yes, it is just a diagram on the principle, I assume you would set the grid and cathode bias to a preset voltage instead modulating it, and intercept the Horiz/Vert oscillators and feed in your X Y signal.
    Max.
     
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