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Crate GLX1200H Blown PT

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  • Crate GLX1200H Blown PT

    I'm working on a Crate GLX1200H that doesn't power up. I found that the 94-011-01 PT wasn't outputting any voltages and it was because there is an open circuit on the primary windings. I couldn't find the PT for sale anywhere. Then I remembered reading about a possible internal thermal fuse on the primary so I decided to slice open the top layer and have a look. Sure enough there's one in there with markings of N124 039 130°C 2A. I determined that it's a Panasonic EYP-2BN124. Datasheet for it is here:

    https://www.digikey.com/en/products/...-2BN124/295818

    My problem is that it is long discontinued and I'm having a little difficulty in finding a suitable replacement. So, any help with a suitable replacement thermal fuse or replacement PT would be greatly appreciated. Thank you!

  • #2
    After checking for bad mains inlet connections and testing for high eddy current is not the problem, I would fit one of these https://uk.rs-online.com/web/p/thermal-fuses/1245061/
    Mouser will have equivalents I expect.
    Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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    • #3
      A quick google for thermal fuse yields:

      https://www.amazon.com/SF129E-SEFUSE...5903320&sr=8-5

      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        Thank you! With those two options being 5A and 10A, is it a problem having higher ampacity than the original 2A device? Or is it that the temperature rating is the main function of these?

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        • #5
          The temperature is what opens it, the ampere rating is more about what it can handle rather than a protective spec. The transformer current is not what opens the fuse.


          With different shapes available, replace yours with one of the same shape.
          Education is what you're left with after you have forgotten what you have learned.

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          • #6
            Originally posted by Enzo View Post
            The temperature is what opens it, the ampere rating is more about what it can handle rather than a protective spec. The transformer current is not what opens the fuse.


            With different shapes available, replace yours with one of the same shape.
            Correct.
            Eddy currents make the transformer get warm and cause buzzing. Shorted turns, make the transformer get warm/hot and produce more shorted turns and more heat.
            Bad mains connection, sparking etc, will heat the transformer and take out the thermal fuse.
            Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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            • #7
              Internal transformer temperature is increased by its power losses, being:

              1) Iron (core) losses, comprised of magnetic hysteresis and eddy current losses.
              Core losses depend on primary voltage and frequency, but not on loading.
              So they can be measured at no-load.
              Raised mains voltage can significantly increase core losses.

              2) Copper losses or IČR losses. These increase with the square of the load current, so twice the load current means 4 times copper losses.

              Often PTs are designed for equal core and copper losses at rated power.
              - Own Opinions Only -

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              • #8
                It could also be that the thermal fuse has just failed on its own without reaching its rated temperature. I've come across this problem with domestic appliances and office machinery.

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                • #9
                  Yes, any part can fail at any time, even thermal fuses.
                  Education is what you're left with after you have forgotten what you have learned.

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                  • #10
                    Thank you for the explanations and links! I'll let you know how it goes.

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