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

 

**A variety of nichrome, perhaps?

Trevor Wilson

 

"Trevor Wilson"

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





....... Phil

 

**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

 

"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

 

**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

 

"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