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What fuse wire?

Discussion in 'Hobby Electronics' started by Phil Allison, Apr 29, 2008.

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  1. Phil Allison

    Phil Allison Guest

    Hi to all,

    common glass tube fuses like 3AG and 20x5mm types are made with a variety of
    wires inside - mostly it is tin plated copper for fast acting " F " types
    and either pure tin or thickly plated tin over copper for the slow or "T"

    Tin has a much lower melting temp than copper, so the wire can be thicker
    for a given rating and this gives it more thermal inertia needed for
    "slo-blo" action.

    But what sort of wire is used in low current fuses with ratings under 1 amp

    Some 3AG, 250mA "F" fuses I have here use a single strand of silvery
    coloured wire with the following characteristics:

    Cold resistance = 2.9 ohms

    Resistance at 250mA = 5.8 ohms

    Resistance when red hot = 10 ohms

    Wire diameter = 0.04 mm ( 1.6 thou )

    Resistance computes as 7.7 times that of pure copper.

    Wire is non magnetic plus it flames at the point of opening.

    Wire is soldered to the end caps.

    ...... Phil
  2. **A variety of nichrome, perhaps?

    Trevor Wilson
  3. Phil Allison

    Phil Allison Guest

    "Trevor Wilson"

    ** No way - NiCr has a near zero tempco of resistance.

    ....... Phil
  4. **Ah, bugger.

    Here's a blast from the past. I just posted 2 ICs to Gil McPherson. Betcha
    remember his amps. Best damned guitar amps I've ever worked on. Phoenix. One
    came in with a buggered output transformer. I took it down to Special
    Transformers and the guy went ballistic. "13 interleaves!" He said. "WTF was
    this guy thinking?"

    Trevor Wilson
  5. Phil Allison

    Phil Allison Guest

    "Trevor Wilson"

    ** Wouldn't one of the Hammond OTs from EVATCO do the job ?

    Or one of the 100 watt Marshall types ( MOP100) from WES ?

    ....... Phil
  6. **It was at least 30 years ago that I worked on the Phoenix. Long before WES
    was in existence. I recall that the guy who owned it was quite particular.,
    I liked the sound of the thing. I was reluctant to make major alterations. I
    had it re-wound and made him happy. Gil is into RF stuff in a big way

    Trevor Wilson
  7. Phil Allison

    Phil Allison Guest


    ** Chromium has the right sort of resistance value - but is non
    solderable, has a very high melting temp and is brittle rather than soft
    like the wire in fuses.

    ...... Phil
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