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Design CRT Testor Restorer

Discussion in 'Electronic Design' started by Gordon Gaskell, Feb 9, 2004.

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  1. I hope to design and build a picture tube testor. I need information
    on grid biases and currents. Information and book and publisher
    recommendations will be appreciated.
    Gordon Gaskell
     
  2. Your subject line also says 'restorer'.
    I have restored a lot of color and BW CRT in the long ago past this way:
    Take mains, rectify (one diode), large electrolytic cap, for
    220V then a 25 W lightbulb from the plus.
    Heater transformer, normal voltage (do not use higher voltage then specified).
    Let CRT heat up, - on cathode, other end 25 W bulb on grid 1.
    Wait till lightbulb lights up (3 -10 seconds).
    If it glows steady release.
    You are done.
    For color CRT do for each gun.
    80% of the time this will fix it.
    (Or more).
    You need to get some feeling.
    The more expensive onses have no single extra feature worth the price.
    Jan
     
  3. CBarn24050

    CBarn24050 Guest

    this takes me back to my childhood. Im a bit suprised it's worth doing these
    days.
     
  4. Thank you for your response. I am thinking of using a variac or
    transformer to heat filaments and with our US mains of 120 volts RMS a
    line voltage recifier doubler will provide 330 VDC grid supply, a
    series resistor will limit current and provide current measurement
    with a voltage drop reading. When I know the current desired and what
    grid to connect to I can calculate a resistor rating.
    Gordon
     
  5. WARNING! the use of a 15 W (or 25) 220V lightbulb, these work
    as current limit constant current source (and visual indication).
    Much better and faster then a resistor and milliamp meter.
    So get a 220 V bulb in your case, or one with much lower wattage,
    say perhaps 8W, if you use a 110V one (or 2 in series perhaps?)..
    In light bulbs the cold resistance can be as little as 1/10 of the warm
    resistance.
    In this system the light bulb does not go full on if tube OK.
    JP
     
  6. N. Thornton

    N. Thornton Guest


    You can do all this but those zappers are not the best way to
    rejuvenate tubes in most cases. The zappers cause picture smearing,
    and boosted tubes usually go downhill much faster after boosting this
    way - and when they do, the smearing makes them unusable.

    In most cases its better to put another turn on the LOPTF to boost the
    heater voltage. This restores proper performance, with no accelerated
    degrading and no smearing, and is a long term fix rather than a short
    term bodge. It also needs no more equipment than a bit of well
    insulated wire and a slobbering iron.

    On an experimental set I hit it with +70% and remarkably it worked
    well, and for a long time too. It was a nice TV but there was almost
    nothing visible on screen at all. I kept it, wouldnt pass something
    like that onto anyone else.

    Heater boost TFs used to be fitted regularly way back when, but the 10
    or 20% boost was very conservative: 33% is much better.


    I said in most cases: if you have an internal interelectrode short you
    need to use the zapper, and if you have a heater to cathode short you
    need a heater iso tf. And there is the one tube in a thousand that
    cant take the higher heater power, due to the plastic coil assy
    running hot already, so heater boosted sets must always be properly
    tested for safety in that area.

    OTOH the zappers are an effective way to extract silly amount of money
    from ignorant techs.


    Regards, NT
     
  7. Oh, but here I disagree.
    Bad practice to raise the heater volts.
    I have seen it, but it does not fix cathode pollution (burn of the bad stuff).
    Only overheats the tube.
    No flame war on this, I think I have done around a 100 tubes over those years
    with the light bulb and DC.
    None of them came back under guarantee. All where 100 % focus.
    Some color tubes you could not get the color balance, then I would replace tube.
    Very rarely the tube would not come 'to live', maybe once or twice.
    For all I know most TV done that way lasted again more then a year or even 3.
    Good deal for a customer, if only alternative is new tube or set.
    Especially because prices were falling and falling of new sets.
    Wait a year, and have the reactivation costs back 3 times.
    Maybe in some 3rd world countries this method will still be very valuable,
    although TVs are now so cheap they almost give them free with a pizza :)
    JP
     
  8. Leeper

    Leeper Guest

    The fancier rejuvinators/restorers also had the ability to blow slag out of
    the beam
    path, in many cases though, an un-trained technician would destroy a tube
    doing this.
     
  9. N. Thornton

    N. Thornton Guest


    Well, it sounds like our experiences differ. I've seen many problems
    caused by reactivation, many sets scrapped because of it, and only one
    case of a problem from heater V boosting. Its also known that there
    are many tubes that just wont respond to reactivation, even short
    term.

    V boosting does not fry the surface off, but boosts the emission of
    whatever surface is there. It is easy to spot a reactivated set: just
    turn the contrast up max, and they smear badly. The problem is they
    deteriorate, though usually not within a 3 month guarantee time.

    I dont want a flame war either, but I'm curious: either something can
    explain our differering experiences, or maybe they're the same, though
    it doesnt sound so.


    Regards, NT
     
  10. Sure, but I dunno WHY.
    Works for me, I teached it to some other engineer, he used it no problems,
    they use it in the UK too, did you use the light blub or some other machine?
    JP
     
  11. Yep, I have seen those units, even used one once, to IMMEDIATLY go back to my
    lightbulb system :)
     
  12. N. Thornton

    N. Thornton Guest

    One of those overpriced professional machines they use in the repair
    shops, I think they cost £50 a time for the tube base adaptors, but
    the techs wouldnt hear a word against it.

    Regards, NT
     
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