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JCM800 2203 fuses

Discussion in 'Marshall Amps' started by Tomiuks1902, Jul 28, 2021.

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  1. Tomiuks1902

    Tomiuks1902 New Member

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    Hey! I’ve got a reissue JCM800 2203, from the early 2000s. I’ve been having issues with a fuse blowing, and am currently getting my father in law (retired electrical tech) to problem solve the issue. What he’s come across is in the schematics for the amp, it clearly states that the mains fuse are supposed to be 6.3A for 220 and 3.15A for 110V. Now, on the back of my amp it clearly states 3.15A for 220V, and 6.3A fuse for the 110V. Was wondering which is correct, if it’s the schematics (which I assume it is), or the back panel of the amp? Thanks!
     
  2. marshallmellowed

    marshallmellowed Well-Known Member

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    My 2203x, which I purchased new, has a 250V / 6.3 amp mains fuse. I'd go with what's marked on the back of the amp, schematics have been known to have errors. Here's a shot of my schematic...

     
    Last edited: Jul 28, 2021
  3. Tomiuks1902

    Tomiuks1902 New Member

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    Those schematics indicate the 6.3 for 220V, and 3.15 for 110V, which is what my schematics say, so are both schematics wrong? And I should do as the amp says, which is opposite? Sorry, I’m electrically incapable, but I’ve added a shot of my amp
     

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  4. marshallmellowed

    marshallmellowed Well-Known Member

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    I can tell you that I removed my fuse, and it's a 250V 6.3 amp, which is what the amp came with. If I were to replace it, I would replace it with the same, regardless of what's on a schematic. What came out of your amp, and what prompted you to replace it?
     
    Last edited: Jul 28, 2021
  5. RLW59

    RLW59 Well-Known Member

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    Volts times amps equals watts.

    At 220 volts with a 6.3 amp fuse, if there's a short in your amp it would draw 1386 watts from the wall before the fuse blows. (Your amp catches fire.)

    At 110 with a 3.15 fuse, the amp can only draw 346 watts before the fuse blows. (The inrush current at start-up blows the fuse every time you turn the amp on.)
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    110 at 6.3 = 693 watts. 220 at 3.15 = 693 watts. Neither fuse will blow at start-up, and if the amp malfunctions both fuses will blow before more damage is caused.

    The point of different fuse amperage for different voltages is to give the same wattage limit.

    So yes, the schematics are wrong and the amp's labels are correct.

    110v at 6.3 = 220v at 3.15
     
    Last edited: Jul 28, 2021
  6. RLW59

    RLW59 Well-Known Member

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    BTW, you can use a 220v/6.3A fuse for 110 wall voltage. (Or 250 volt.)

    It's the amperage going through the fuse that matters. Current/amperage is what heats up the fuse and causes it to blow.
     

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