Phil Allison wrote:
>
> "Trevor Wilson"
>
> >>I wonder what the DC resistance of a 250mA fuse might
> >> be?
> >
> > **Depends on the fuse. I just measured half a dozen 0.25 Amp 3AG
fuses.
> > They ranged from 12 Ohms up to 15 Ohms. COLD.
>
> ** That is an unbelievably high resistance value - not at all
consistent
> with a 250mA fuse.
I have NEVER EVER measured any fuse ranging from 12 ohms to 15 ohms
cold.
All fuses are ARE low resistance compared to the circuit resistance
where they are fitted.
The lower amp types such as 0.25A are simply fine wire which will get
hot and fuse open
if current exceeds about 0.3A for some time.
A peice of very fine wire only 20mm long has low resistance.
TREVOR WILSON SPREADS MORE LIES AND BS ACROSS THE INTERNET AGAIN.
>
> Some no brand, 1/4 amp 3AG fuses I checked ranged from 3.5 to 4.5 ohms.
>
> These 20mm "T" or delay fuses from Bussman are speced at 0.66 ohms for a
> 250mA size:
>
> http://www.farnell.com/datasheets/81115.pdf
>
> The specs show that R rises to 1 ohm at rated current.
>
> > ** Fuses act as non-linear resistors. They get hot and change
resistance.
>
> ** Speaker voice coils do that too.
Indeed, and the dc resistance in in series with the inductance of the
voice coil.
Its a somewhat complex model, but so what if resistance varies with
temperature?
The variation in resistance needs to occur during each wave cycle for
added distortion
to occur. If the temperature stays virtually constant the resistance
remains fixed and
there is no resulting distortions.
One can hace a light bulb in series with a speaker, and at low levels
you'd
never know, but at highg levels the bulb turns on with the higher
current and its
resistance dramatically increases, thus causing a compression effect on
the signal waves.
Bulbs were often used to limit signals to speakers.
Patrick Turner.
>
> ..... Phil
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