Replacing aged fuses?

[Axtman]

I have a friend that works on amps. He says that he almost always replaces the fuses in the amps he repairs. He says that the fuses might be thermally stressed and might blow early. He said he has had a customer where the fuse prematurely blew.

I do not dispute this practice. I guess better safe that sorry.

With me about 1/2 the time the fuses are the wrong value or are automotive fuses, so I replace them anyway. If a fuse looks really corroded or then end cap is loose or has "gone to air", then I will replace it.

[Tom Phillips]

I only replace blown, wrong value and obviously damaged fuses.
I have never had a call back because an old fuse blew just because of stress.
Given the design practices followed in the guitar amp business. The are many parts that are under stress.
I you buy into the view of replacing stressed parts then where do you stop? For example, do you replace the output transformer because the customer once pulled the cable out of the speaker cabinet while the amp head was on?

That's my view anyway.

Cheers,
Tom

[The Dude]

Agree, Tom. Pretty much my modus operandi, also.

[trobbins]

What would 'aged' imply? Aged as in likely the original installed fuse from the 1960's, or for equipment that has been in regular use for the last decade or so, but the fuse appears to be 'modern' (ie. made within the last few decades)?

There would likely be some confidence that a fuse made in the last few decades was manufactured with better quality control than one from say 60 years ago.

Some manufacturers likely sized their fuses to avoid blowing except for a gross failure - ie. not aimed to protect some internal failures that may stress internal parts, but would unlikely cause a fire.

[Mick Bailey]

In the UK the main issue is we have fused mains plugs and the default value is 13A (the maximum for a plug). We''re on 240v, so that's a lot of power to dissipate under a fault condition. I always check and install the correct fuse.

Where an amp has been a fuse blower more often than not there's been an escalation in the amp's own fuse rating to 'fix' the problem and sometimes with expensive consequences. However, if a fuse is correct I've never replaced it. Rarely, a manufacturer has increased a fuse value to prevent nuisance blowing. I had a case where the amp was marked up with a 500mA HT fuse and a 1A was fitted, so I reverted it back to 500mA and it blew fairly soon afterwards. No fault found, but I found a service update that said to uprate the fuse. I printed up a vinyl label with the new rating to prevent confusion.

[mozz]

No. Same with diodes, unless they are bad they stay.

[Helmholtz]

It seems possible that fuses fail from long term fatigue (similar to an incandescent bulb but on a way longer scale).
I couldn't find real data on expected lifetime, probably because there are too many influencing factors, like continuous current, number and strength of large I²t surges, ambient temperature, vibration etc.
Some fuse manufacturers recommend to replace a fuse after 20 to 30 years of use (may vary between different types).
Just google "lifetime of a fuse".

It has been observed that the resistance of the fusing element (wire) slowly increases with use, making the fuse more sensitive.

Some literature: https://pure.tue.nl/ws/files/1469141/449473.pdf

[Bill Moore]

In the automotive world, back in the stone age using glass fuses, some of the larger values could be "stressed", usually on a high amperage circuit. Heat would melt the solder, (especially horizontally mounted), the solder would pool in the bottom of the fuse, and eventually open the circuit. Modern fuses are much more reliable with solid mechanical connections, but I guess we're stuck with glass fuses in our electronic circuits!