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Thread: Crate GXT100 Hybrid Amplifier

  1. #1
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    Crate GXT100 Hybrid Amplifier

    Sorry for the old members. I have no experience in audio electronics.
    I have this GXT100 amplifier since 98. I have had some problems in the past but all have been "fixed".

    1- channel selector did not work. (3 times in 30 years).

    2- Transformer burned. "reconstructed". (some 4 years ago).

    3- speaker burned the coil. (last year).

    4 - I now have a series of problems, several of the test points of the schematic do not match.

    My question for this moment is whether the schematic (service manual) is 100% correct.
    Since some components are not present in the physical circuit. for example (Q28).

    Another estrengertinks (for me). On poweramp circuit, exactly the TP21 says I have to have 36.5 + V, but the source is negative. And that's what I got. 36-V.

    schematic is it correct?http://elektrotanya.com/?q=showresult&what=crate

  2. #2
    Lifetime Member Enzo's Avatar
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    I do not see a Q28 on the schematic, and in fact there is a note on page 1 that the highest number used was Q27. SO I don't see how it is missing. If the board has Q28 printed on it, perhaps another model uses that board too, and Q28 only exists on that model.


    TP21 obviously was meant to be negative, just a misprint.

    I believe schematics until I have a reason not to. For example, if there is an error drawn in the reverb circuit, and I am not working on the reverb circuit, then I no longer care about that drawing error.
    Education is what you're left with after you have forgotten what you have learned.

  3. #3
    g1
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    Enzo, perhaps you have an earlier schematic that you can post? The one I'm attaching from his link shows Q28 (upper left pg.1) and mentions it's addition in the notes. Maybe he has the older version that your schematic matches?
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  4. #4
    g1
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    Never mind, I see the 'last used' Q27 note in upper right area as well, so Enzo is probably looking at the same drawing.
    Q28 is shown above IC4/TP14 area in upper right of schematic.

    Castroalien, there is probably an earlier version of the schematic from before Q28 was added. (mid '97)
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  5. #5
    Lifetime Member Enzo's Avatar
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    I looked and looked and never spotted that Q28. In any case it is just a mute, so if it is missing it won't cause a problem, other than maybe a noise when switching.

    I just used the Elektrotanya link. I found the GXT100, but also looked for GTX100. I wound up with the same drawing, but while one was pieces in GIF, the other was a PDF of the whole thing.
    Education is what you're left with after you have forgotten what you have learned.

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    Sorry for the delay in replying.

    Q28 is present in the scheme but not on the board physically for sure should be an old revision of this. (I even have another version of these schematics that has this Q28).

    While at TP21, as I have no experience in audio electronics. I spent a long time looking for horn on horse's head, thinking that this was a problem.

    I will post more information about the problem soon.

    Thank you very much for your´s attention.

    Best Regards.

  7. #7
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    Quote Originally Posted by castroalien View Post
    Sorry for the delay in replying.

    Q28 is present in the scheme but not on the board physically for sure should be an old revision of this. (I even have another version of these schematics that has this Q28).

    While at TP21, as I have no experience in audio electronics. I spent a long time looking for horn on horse's head, thinking that this was a problem.

    I will post more information about the problem soon.

    Thank you very much for your´s attention.

    Best Regards.
    Other schematic best quality.
    Attached Files Attached Files

  8. #8
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    Crate GXT100 Hybrid Amplifier

    Helow folks neste momento o amplificador encontra-se:
    input .1Vrms /1Khz
    all Tone and gains and level 5 all switches off. exept clean vol level 10.

    Pic dsc-57 TP22 on schematic (+ out from speaker)

    Pic dsc - 59 TP14 (out off Preamp)

    A few days before, before you bring it to work. I did a test on the send and return of this equipment, sending preamp to another amplifier and sound seemed relatively good.

    I'm in trouble on the pre and power circuit.



    dsc_0259.jpgdsc_0258.jpgdsc_0257.jpg
    Last edited by castroalien; 02-07-2018 at 07:43 PM.

  9. #9
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by castroalien View Post
    Helow folks neste momento o amplificador encontra-se:
    Hi guys, current amp state is:
    input .1Vrms /1Khz
    all Tone and gains and level 5 all switches off. exept clean vol level 10.

    Pic dsc-57 TP22 on schematic (+ out from speaker)

    Pic dsc - 59 TP14 (out off Preamp)
    All 3 show distortion but that does not mean something is wrong, just too high signal drive.
    Lower volume twice:
    1) Until preamp out signal cleans ... speaker out will still clip
    2) keep lowering it until power amp out (speaker +) stops clipping, then riose it again until it barely does.

    A few days before, before you bring it to work. I did a test on the send and return of this equipment, sending preamp to another amplifier and sound seemed relatively good.

    I'm in trouble on the pre and power circuit.
    And what do you say the trouble is?
    Your description of symptoms, what you hear, not what you think is the cause.

    PD: você sabe que Alien é marca registrada do amigo Ronaldo Brito de SP?
    g1 and castroalien like this.
    Juan Manuel Fahey

  10. #10
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    "Hi guys"

    The sound is cracking even at low volumes.

    I'm just following the service manual.



    Rpd: Não, não sei. ja ouvi falar da marca. Se ele tiver o registro dela antes deu ter criado minha conta de e-mail em meados de 94.

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