EHT - substitute

Discussion in 'General Electronics Chat' started by ectronica, Aug 10, 2009.

  1. ectronica

    ectronica Thread Starter New Member

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    hi guys...
    i own an old GRUNDIG st63-701 nic/top 25" television set..
    now it totally dead - (EHT) I cant find any EHT - in any local shops..
    is there any substitute?/
  2. beenthere

    beenthere AAC Fanatic!

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  3. n9352527

    n9352527 AAC Fanatic!

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    Extra High Tension. Are you referring to the EHT transformer?
  4. beenthere

    beenthere AAC Fanatic!

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    Perhaps not too likely - it's a 25" set, so HV will be on the order of 26 - 27 KV. That's not extra high.
  5. AlexR

    AlexR Well-Known Member

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    27Kvolt may not be classed as EHT (Extra High Tension) in the power transmission field but in television receivers that is what it is called.
    This goes back to the days vacuum tubes where the term EHT was used to differentiate the picture tube voltage from the normal HT (about 250V) that was used to drive the rest of the circuit.
  6. KL7AJ

    KL7AJ E-book Developer

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    EHT=Electron Holding Tank :D
  7. ELECTRONERD

    ELECTRONERD Senior Member

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  8. rjenkins

    rjenkins AAC Fanatic!

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    On older sets, the Line output Transformer was also used as a multi-voltage power supply and provided all voltages other than basic 'rectified mains' which the line oscillator and output ran on.
    (Line Output Transformer = LOPT or Flyback Transformer)

    Newer sets usually have a switch mode power supply to give mains isolation and the LOPT is just to run the line scan coils, supply the other tube voltages & generate the EHT supply.

    Is it completely dead (older type) or do you have sound & be able to change channels etc., but no picture (newer type, or only the EHT rectifier failed)?

    Can you see a (possibly faint) orange glow in the back of the tube neck? This will show if the low voltage filament power is working and give another clue where the fault could be.

    Both types use high voltages, even discounting the EHT.. In addition the older ones are not isolated from mains power and you could get a shock from any part of the circuit.

    Also, older ones TVs did not have a discharge resistor on the EHT circuit and the EHT connector (with the rubber cap) on the side or top of the tube body could have dangerous voltages on it for weeks or even years after it last worked.

    Be extremely careful, getting zapped hurts! (or worse).

    Have a look at this page for an example line output transformer; click on the small circuit diagram, you will see the transformer with the V+ input and switching transistor on the top left winding, multiple voltage outputs to run other parts of the circuit, and the EHT winding on the right. This one has the EHT rectifier intergral to the transformer.
    http://www.electronic-spare-parts.com/catalogue/line_output_transformers/hr_6173.html
  9. ectronica

    ectronica Thread Starter New Member

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    I dont Hav any deeep knowledge in Elecronics,, i Used the term EHT because My Friend told me like this,, When I asked him this SAme Q -- "What is EHT?" He told me Same As LOT/FET.

    NowComing Back to MY TV SET' condition , Now its Totally Dead...
    During the initail Stage - I got some Noise frm the "LOT" like crackling and HISSes..
    When I inspected it , I saw small crack on the LOT,, i searched a lot of places , for a new one but disappointment was the result..
    I cant leave tat TVSET, because I love it & tat was our first Big screen tat we own.. MOre over it support multiple AV Socket,,, & Component input Connectors,, Computer Connectivity,& Also HAv Built in Teletext Decoder(Not useful here.. :) ) PLease Help me...
    Is tat posssible to block that crack on the EHT//??
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