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Thread: Fuse resistance

  1. #1
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    Dec 2009

    Fuse resistance

    I noticed that after replacing the cathode fuses in an Engl amp the power tube LED was flashing in sequence to playing. The only way is if there's either a circuit fault or the fuses have a high enough resistance for the voltage drop to trigger the LED circuit. I re-checked the amp and checked the fuses - they all read 56 Ohms, which really annoyed me as I'd just bought them and had to make up a minimum order charge as I was out of stock (T63mA).

    I did a further check and the resistance holds out even at their rated voltage and close to their capacity. Temporarily swapped them out for some T100mA and no problem.
    Last edited by Mick Bailey; 02-19-2018 at 06:41 PM.

  2. #2
    Lifetime Member Enzo's Avatar
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    May 2006
    Lansing, Michigan, USA
    Really low current fuses like that do normally show resistance. My HP meter used 32ma fuses.

    So other than the LEDs blink, what problem did the smaller fuses cause?
    Education is what you're left with after you have forgotten what you have learned.

  3. #3
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    Dec 2009
    No other problem that I can see, though the 'scoped output increased just a little with lower resistance fuses. The originals read a little over 10 ohms so I've ordered another lot from a different supplier who lists the resistance. I would think that 56 ohms in each cathode circuit would introduce a little more NFB, as it's unbypassed. The main issue is I don't want to return the amp to the customer with a flashing LED that didn't flash before.

  4. #4
    g1 is offline
    don't forget the joker g1's Avatar
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    Feb 2010
    Canada, somewhere north of Fargo
    I remember some of the slow blows used to have little resistors inside, maybe some still do.
    Could you just tell the guy it's the 'back-off!' light?
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  5. #5
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    Dec 2009
    I actually prefer the flashing LED. It just needs to be blue to make it a 'now' thing.
    g1 likes this.

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