Help! Jvm205h Problems

Discussion in 'The Workbench' started by Spudvader, Aug 16, 2018.

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  1. Spudvader

    Spudvader New Member

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    Hey,

    My amp was making a crackling sound after a while of playing so I changed the power tubes but the problem never went away, then one day the amp refused to work. I changed the pre amp tubes but still nothing.

    I can hear the amp humming when on max gain on the crunch channel and I get sound from the fx loop when plugging into there in both send and return, I only hear sound from return in the right fx loop. I have also tried resetting the amp and swapping out the fuses but still no change.

    Now after trying different things, like changing the fuses and swapping out tubes, the amp now makes a short sharp, loud, squeak/squeal when turning the amp on.

    I usually use the amp with the aux output but I have tried plugging into a cab and no difference.

    I'm completely perplexed, any help would be greatful.

    cheers
     
  2. Spudvader

    Spudvader New Member

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    This isn't my video but this is the same crackling that I had.
     
  3. ampmadscientist

    ampmadscientist Well-Known Member

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    "My amp was making a crackling sound after a while of playing..."

    (need 2 cables) Plug a guitar cable into (between) send and return of both effects loops.
    1. Bypass the "power amp insert / serial effects loop" with a guitar cable. (as above)
    and at the same time
    2. Bypass the serial parallel effects loop with a guitar cable as above.

    3. Set the MIX control fully DRY.

    4. Plug a speaker into the amplifier, make sure the speaker is the correct impedance.
    Never use a guitar lead to connect a speaker. Always use a real speaker cable.

    You are not allowed to run the amp without a speaker (or load resistor etc...), ever.
    A tube amp must always have a speaker load and there is no exception.

    5. Now test the amp.
    Is the crackle still there? or is it working normally? Yes or No?

    It's quite possible that the power amp was damaged from running the amp without a speaker.
    This can fry the tube sockets, tubes, output transformer.

    But it may just be a loose connection (like bad effects jacks etc), and maybe you lucked out.
     
    Last edited: Aug 21, 2018
  4. Spudvader

    Spudvader New Member

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    Nothings sounds different because I get no sound from plugging in the front, it's like it doesn't even register that there is something plugged in the front. Usually you would hear a small crackle or something when you plug into the amp when it's on but there is nothing. If I plug my guitar straight into the "in" on either effect loops then I hear the guitar.

    If I play around with the gain or the EQ I can hear the hum changing sound.
     
  5. ampmadscientist

    ampmadscientist Well-Known Member

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    Did you bypass the effects loops? yes or no?

    It's quite possible that the power amp was damaged from running the amp without a speaker.
    This can fry the tube sockets, tubes, output transformer.
     
    Last edited: Aug 24, 2018

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