Jcm 2000 Tsl 100 Fuse Replacement Inquiry

Discussion in 'The Workbench' started by uglycustoomer, Jun 11, 2018.

  1. uglycustoomer

    uglycustoomer New Member

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    Hello - one of my fuses blew and I replaced it with a MDL 2A -250v Fuse. Once I turned the amp on and played for a few minutes, I noticed that the volume was very low. The amp felt extremely hot and one of the tubes blew.

    The back of the amp by the fuse box says it can take the following,

    T2A - 230v
    T4A - 120v

    I live in the U.S.

    Can someone recommend which fuses would be OK for my amp? Having a really tough time finding an exact match.

    Thanks!
     
  2. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Being in the U.S. your utility supply voltage is 120VAC so the amplifier mains fuse should be time delay/slow blow 4A.

    If you are also blowing power tubes then the amplifier will need more attention as well as new tubes and bias check.
     
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  3. Jethro Rocker

    Jethro Rocker Well-Known Member

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    Also a fuse rated at 250V is fine as long as it's a 4 amp. Don't look for a 120v T4 fuse if they're hard to find.
    As stated above, the extra heat and blown fuse may indicate a dead tube so don't just change the fuse and continue.
     
  4. uglycustoomer

    uglycustoomer New Member

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    Great. Thanks for the feedback!
     
  5. GT08

    GT08 Active Member

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    The voltage written on a fuse is just the Maximum operating voltage for that fuse, so 250v is fine.
    The important thing is current. At 120v mains supply the fuse must be 4 amp.
    VERY IMPORTANT.....all mains fuses must be special SLOW BLOW fuses, available on line no problem.
    If a correct value fuse blows you have a problem with the amp/valves.
    Rock n' roll
     
  6. The Dose of Harmony

    The Dose of Harmony Member

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    how its it going with your amp? I havent heard you about your bias before and after the fuse , you might need to check your amp in a deeper way! if its or was running hot
     
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    Troubleshooting required.

    1. Take the output tubes out. Replace the fuse.
    Turn the amp power on, but leave standby off.
    3. Measure DC voltage at pin 5 of output tube socket (note this voltage). This should be a negative DC voltage.
    If there is no negative voltage on pin 5, the bias has failed.
    If the bias failed you cannot operate the amp.

    4. Continue to measure voltage at Pin 5 of output tube socket.
    Turn the standby on.
    Note the difference in pin 5 DC voltage between standby off, and standby on.

    5. If the negative voltage Pin 5 changes to a positive voltage, (or changes substantially) when you turn standby on,
    then you probably have a defective circuit board.
    If you have a defect board, you cannot operate the amp till the problem is repaired.

    6. Allow the amp to run for 1 hour or more, and monitor the pin 5 bias voltage. If this bias voltage drifts when standby is turned on, then the board is probably defective.
    If this defect board condition exists in your amp, then the output tubes will be destroyed, and the fuse will blow.

    7. No
    do not replace output tubes until you have tested this......
    the bias voltage must be steady... :nono::nono::nono:
    otherwise ---- kiss the new tubes goodbye.
     
    Last edited: Jun 14, 2018 at 2:06 PM
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  8. The Dose of Harmony

    The Dose of Harmony Member

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    you are the best one! short ,clear and to the point !!! love it!
     
  9. ampmadscientist

    ampmadscientist Well-Known Member

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    This is what happened the last time bias drifted.

    [​IMG]
     
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  10. royslead

    royslead Well-Known Member

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    VERY helpful info, Amp' !
     
  11. 6StringStewie

    6StringStewie Member

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    In the US, you will need the following fuses:

    1 Mains Fuse - 4 amp slow blow 6x30mm
    1 HT Fuse - 1 amp slow blow 5x20mm
    4 Heater Fuses - 6.3 amp slow blow 5x20mm (located inside the chassis)

    For reference, these are the fuses I use. Some are ceramic and some are glass. Either are fine.

    20180617_212609-1008x756.jpg
     
  12. 6StringStewie

    6StringStewie Member

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    Your tube blowing is not from the wrong size fuse. It was either a tube that went bad or you encountered the bias drift problem associated with these amps. Where are you located? If you are close, I could stop by and take a look at your amp.

    Stewart
     

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