kev
valued member
Posts: 12
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Post by kev on Jul 19, 2016 17:32:52 GMT
One of my power amps blew a fuse & I am preparing to take a look at it. The fuse is a 7A/250V fast acting, but it has the crimped (sine wave) wire inside & I am wondering if it is different than one that has a straight piece of wire. It's not a spiral like a slo blo. If I learned it in school, I've forgotten the reason for the wiggly wire, unless it insures that the gap opens quickly when it blows??? It's a Little Fuse brand & all I am finding locally have straight wire. Here is exactly what is printed on the fuse. LF. 7A/250VP. They are the standard 3AG cartridge fuses.
Thanks,
kev
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solderdude
Administrator
measureutternutter
Posts: 4,881
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Post by solderdude on Jul 23, 2016 8:38:59 GMT
It would depend on where the fuse is and 'how' it blew.
If there is one in each power supply line and one of them simply went open circuit and doesn't appear to have gone out with a 'flash' then chances are replacing the fuse will make the amp work again. If the glass is all 'black' or it appeared to have at least gone with a 'bang' and the amp wasn't accidentally shorted at the output by accident at that time than chances are the fuse blew with a good reason and one or more output devices may have blown (taking God knows what with it).
If the fuse is in the output path then replace it and connect a cheap speaker while testing !
When there is an 'F' it is a fast acting fuse and should be replaced with a fast one. Usually these are found after the smoothing caps (in series with the output devices or the amplifier circuit) When it has SB or T on it they are slow-blow. These are usually found in the secondary winding part before the rectifier.
The wiggly wire is a spring that creates a wider 'gap' so the fuse cannot 'spark' when there is 230V across it when 'open'. If the gap was very small and there weren't a spring actions it could spark shortly and thus not act as a quick fuse.
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kev
valued member
Posts: 12
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Post by kev on Jul 23, 2016 20:25:22 GMT
Thanks for your reply & info. I suspected that the wiggly wire fuse was designed for the reason you mention. I can't find any. Everything I find is a straight wire. The amp is going back to Bryston because it blows the fuse with nothing connected. Probably an output device. Thanks, kev
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