What fuse wire?

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

Reply to
Phil Allison
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**A variety of nichrome, perhaps?

Trevor Wilson

Reply to
Trevor Wilson

"Trevor Wilson"

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

...... Phil

Reply to
Phil Allison

**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

Reply to
Trevor Wilson

"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

Reply to
Phil Allison

**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

Reply to
Trevor Wilson

Chromium?

Reply to
DavidW

** 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

Reply to
Phil Allison

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

Reply to
DavidW

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