What fuse wire?

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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"
types.

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





Re: What fuse wire?

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**A variety of nichrome, perhaps?

Trevor Wilson



Re: What fuse wire?

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





......  Phil






Re: What fuse wire?

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**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



Re: What fuse wire?

"Trevor Wilson"

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

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



......   Phil



Re: What fuse wire?

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**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
nowadays.

Trevor Wilson



Re: What fuse wire?
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Chromium?



Re: What fuse wire?

"DavidW"
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** 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






Re: What fuse wire?
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Then it looks like it's some alloy, which could be anything, or maybe strontium.
I don't know the solderability of strontium.



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