Finished TV Oscilloscope/ VU Meter not proper

Discussion in 'The Projects Forum' started by PartyLine4, Jan 15, 2013.

  1. PartyLine4

    Thread Starter New Member

    Jan 12, 2013
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    I just turned an old 5 dollar CRT into a VU meter. I noticed however, the amplitude must be VERY high to get a satisfactory waveform.

    I have seen little tid-bits of info regarding these " amplifiers " that could possibly be built into this old TV.

    I am eager to build, I am eager to learn.

    Some proper guidance is what I am asking for.

    Another thing, The Tv of course now has 2 probes sticking out of it. I would think that I could hook this up in parallel with my phones speaker to give me a cool effect.

    Could it be done?

    Considering the probes are not putting out any current I don't see why not.

    In case you're lost by now the main questions are:

    Guidance to building an amplifier for the CRT

    And if I can hook this up to my telephone. ( I have an old GTE Model 80 )

    Thanks a bunch!
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    How about a little more information about your $5 CRT. A CRT without supporting circuits won't do much.
     
  3. PartyLine4

    Thread Starter New Member

    Jan 12, 2013
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    *realizes thread is shot*

    Just forget it.
     
  4. tshuck

    Well-Known Member

    Oct 18, 2012
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    675
    You are a sincerely impatient person. This is an international forum, meaning that its members are in all different time zones and points in their day.

    Try be a bit more patient and see what happens instead of jumping down everyone's throat for not giving you the solution when more information is deemed necessary.
     
    PartyLine4 likes this.
  5. PartyLine4

    Thread Starter New Member

    Jan 12, 2013
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    OK, moving forward.

    The TV is very similar in many ways to those of similar size. The CRT is hooked to the large voltage generator as on all CRTS and the vertical sweep has been removed.

    Has many Potentiometers that adjust the sweep rate and such.

    Can't seem to increase visual amplitude without making physical amplitude very high.

    The circuit is all hand soldered.

    Pictures would be difficult to coordinate

    But if you want to see a particular part of the circuit I am glad to snap a few photos.
     
  6. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    Ok, now we know more about what you are starting with. Are you looking to see a trace similar to what an oscilloscope would show? When you say you want to make a VU meter, do you mean you want to see the waveform of audio? What do you have the two probes attached to at this time? I am assuming that you have magnetic deflection coils, so you are correct when you say you need amplification of any input in order to drive those coils. The more you can tell us about what you have and what you want, the more help you will get.

    Is this what you want to do...... http://www.instructables.com/id/Fully-Functional-Television-Oscilloscope/?ALLSTEPS
     
  7. DickCappels

    Moderator

    Aug 21, 2008
    2,651
    632
    This may be a small amount of help; the vertical deflection coils tend to require amps of drive current. Some of the higher current output audio amplifier chips might be pretty good for driving your yoke.
     
  8. PartyLine4

    Thread Starter New Member

    Jan 12, 2013
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    I am only using the horizontal deflector at this time.

    The leads can be hooked to the output of a speaker system ( audio amplifier) and shows good read-outs

    Took the TV to my electrical class and hooked it up to an AC variable supply.

    Max screen visible voltage is about .4-.46 VAC. Not much!, but perfect for any audio readouts. If the CRT wasn't so packed with voltage I was thinking that an amplifier could be hooked in series with the input to the deflector.

    So with that being impossible without really expensive resistors and transistors. What am I to do?

    Normal communication sounds from my telephone barely move the signal line.

    Hooking an 8Ω speaker directly to the terminals and yelling into it makes it bounce a little.

    I want it to move greatly with normal voice input. I don't see why I couldn't make some sort of amplifier.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    Do you have a schematic of the TV? You said earlier that the vertical sweep had been removed. How much was removed? If just the sweep oscillator was removed, the vertical deflection amplifiers may still be there. That would greatly simplify your efforts. What is the make and model of the TV?
     
  10. sheldons

    Active Member

    Oct 26, 2011
    616
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    also dont forget that the smps used in your tv makes the chassis live.....any equipment requiring an earth connection will cause expensive damage when connected unless you use a suitable isolation transformer.....make and model of your set needed .....
     
  11. PartyLine4

    Thread Starter New Member

    Jan 12, 2013
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    http://www.youseeitnow.com/acn-3514_tv.htm

    What devices use earth as a ground?

    Thanks for the tip though, I knew real scopes can't be hooked to circuits like that, only " floating " circuits.
     
  12. PartyLine4

    Thread Starter New Member

    Jan 12, 2013
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    From what I can fathom, the vertical sweep oscillator has been disconnected and the horizontal has been put in the vertical's place.

    The circuit has two leads for the CRT for each one ( Horiz and vert )

    I have a pretty watered down view of what is going on.
     
  13. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    If the "horizontal has been put in the vertical's place" you would have a line going from the top to bottom of the screen. Is that what you are seeing?
     
  14. vk6zgo

    Active Member

    Jul 21, 2012
    677
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    You seem to have a problem with terminology!

    A CRT or Cathode Ray Tube is the glass thing that has the picture on the front.
    The box you are playing with is either a TV or a Picture Monitor.

    Using the term CRT for the whole assembly is an annoying habit of some Computer people,& freaks Electronics people out.

    A VU meter is a calibrated meter with,(for a mechanical meter) special ballistics which affect its response time to signals.

    It appears that you are trying to make a fairly basic Oscilloscope.
     
  15. PartyLine4

    Thread Starter New Member

    Jan 12, 2013
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    0
  16. BillB3857

    Senior Member

    Feb 28, 2009
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    So I guess all your problems are solved! That is similar to the project I linked to earlier. Main difference is the link I posted shows an amplifier circuit to help you see things better.
     
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