Iain Churches wrote:
>
> I wonder what the DC resistance of a 250mA fuse might
> be?
>
> I have just been speaking with a guy would told me that he
> has replaced the fuse from the CT of the OPT of his tube
> amp with a wire link, "because the fuse adds to the power
> supply impedance and does not have a linear response"
>
> He could not quote any reference to substantiate this.
>
> I wonder what the audio bandwidth impedance of a
> 250mA fuse might be? -)
>
> Compared to the cost of an OPT, the fuse seems to be a
> good component for such a small investment.
>
> Iain
Fuses between the B+ and a CT on an OPT are not a bad idea.
90% of music from tube amps is from PP,
and while the amp remains fully in class A.
So the non-linarity of the fuse impedance is utterly negligible.
Traditionally, ppl said fuses before speakers were bad because there the
fuse value
might be 4 amps, and the distortions caused by the fuse could be greater
than the those from the amp,
which might only measure 0.001% at a watt or two which is all most ppl
ever use.
A 4A fuse may have 0.01% thd, 10 times more. It doesn't make much
difference though eh.
A piece of small dia copper wire soldered in would be ok except that its
temp varies and hence its resistance.
Maybe not to much though.
Active protection against excessive cathode current works a lot better
though.
The problem with a fuse is at low levels when a speaker wire has frayed
strands causing a short
that isn't noticed, and load becomes less than 0.3 ohms, so the output
tubes or tyransistors cook themselves
even at low levels even though there isn't enough current to blow a
fuse.
Active protection is better.
Patrick Turner.
Patrick Turner.
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