I am sorry but I have to politely but fundamentally disagree with some things being said here.
A fuse and a resistor are totally different beasts in every way and no decent designer will use a resistor in place of a fuse. And without a doubt, though design may have moved on, Heybrook were and are a more than decent manufacturer. Just because the resistor will burn out and cut the circuit with the same ultimate effect as the fuse does does not make them behave the same in doing so.
Bear another thing in mind here, re-read Piglet's Dad's response earlier about 2.7 or 2.8R. He is known for speaking sound technical sense, (usually
), so take his opinion as having merit. Now let's spare a thought to that resistor which you are discussing in terms of its change of resistance on heating.
Not having such things at my fingertips I did a very quick look at some specs just to get a feel, (Farnell catalogue!). I looked for the worst cases and considered a humble carbon resistor, 2.7R, 0.25W. These generally had a temperature coefficient of around 350ppm/deg C. (The poorest temperature coefficient I could find was 1500ppm for a very different beast). Let's say the temperature rise will be 100deg. That means that the resistance will change by 2.7 X 350 x 10^-6 x 100. This gives less than 0.1R, or less than from 2.7R to 2.8R. Now what was it PD said?
And please let's not spread smoke about dynamic changes versus static changes, we are talking about components with considerable thermal inertia here being swamped by the same type of effect in the voice coils and other circuitry.
The percentage power delivered to a tweeter through a half decent crossover is somewhere in the region of 2%-15% depending on source material and crossover frequency. Let's say we have a 100W system driving it. Thinking average power here and not 100W continuous, with a 20dB or 10X difference between peak and average voltage levels, (normally considered sensible), that means a 100:1 ratio of power, (V^2), or about 1W average for 100W peak. Of this let's say 10%, (highish!), is taken by the tweeter branch and about 1/3 is taken by the resistor, (2.7R:6R). That means the resistor is experiencing an average power just below 35mW.
Or I could easily be wrong somewhere, very genuinely, if so please point it out to me as this sort of topic intrigues me. 20W wirewound resistors in place of 0.5W to dissipate 0.035W seems a little - er - "skewed thinking" to me.
Anyone care to comment on the audibility of running your speakers without a lagging overcoat and scarf in winter?