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At the last gig I played the guitarists amplifier head blew a mains fuse and we didn't have a replacement.

We've learned our lesson about having spare fuses, sufficed to say.

Thankfully we had a spare channel on the PA that could power the cabinet so we got through the night without too many problems, but obviously we don't want to have to be opening up amplifiers on stage to switch out fuses in future.

The fuse is rated at 2 Amps (230v).

One idea that we talked about was to fuse the power leads with 2amp fuses, so that if it happened again atleast only the power lead would blow first and we could switch that out or replace it much easier than switching the amplifier fuse. However ideally we'd want to avoid any fuses blowing.

Is there an accepted best practice or strategy for dealing with this kind of thing?

Are surge protectors any help?

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    Maybe the first question you should ask is "Why did it blow"? Was it too hot? (Keep it cooler) Were you pushing it too hard? (Get a bigger amp) Is there something wrong with it? (Get it checked out by a tech) – blindJesse Sep 23 '12 at 19:28
  • it's being serviced by a tech to fix and check that there arent any other problems. it blew 2 seconds after it was switched on, which rules out overheating and pushing it too hard. saying that i've never managed to blow a fuse on an amp by turning it up to eleven lol. Point is, assuming the amplifier is working, is there any precautions I should be taking with the power? i.e if the power lead has a 13amp fuse it will let through enough of a surge to blow the 2amp fuse in the amplifier and might not blow itself. does that make sense? – jammypeach Sep 23 '12 at 19:48
  • Sounds like a power conditioner would help. It'll keep the voltage level despite spikes or sags, and it will trip before your gear does. It's a good investment anyway since so many venues have things like freezers or air conditioners hooked up to the same circuits as their stages, which can actually be heard in your amp. – WLPhoenix Sep 25 '12 at 18:10
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First things first: DO NOT TAMPER WITH ANY INTERNAL FUSES OR ANYTHING THAT CAN CARRY LINE VOLTAGE. It's dangerous, it hurts, and it will be the end of your performance at the most inopportune moment.

The key is to find out why the fuse blew in the first place. A well designed amp these days does not have any internal fuses. I used to design these things for a living and I haven't designed in an internal fuse in 10+ years. Proper protection circuitry should monitor the amp and take it into a controlled shutdown when bad things happen.

So assuming you have an older model, we need to find out what took out the fuse. That really depends on age, type (tube, class A, class A/B, class D) of power stage, brand and abuse scenario. If there really wasn't any abuse involved, something is wrong with the amp and you should have checked it out by a technician. It's possible that you have an intermittent short, which you really want fixed.

Make sure the amp has not been "modified" by some amateur. I have seen an "improved" Fender Champ that put 120 V on the guitar strings when you plug in the AC a certain way.

Adding an external fuse is generally a bad idea: Firstly you have to build a contraption that connects directly to AC which is a) dangerous, and b) illegal in most jurisdictions. Secondly, you need to size the fuse in terms of tripping point (speed, current, recovery time) so that it always kicks in before the internal fuse. That's tricky to do and will also likely trip on the in-rush current of the amp anyway.

It's always a good idea to bring an outlet tester and a digital multimeter to a gig to check the AC outlets on the stage (which can be questionable). Check whether the voltage and grounding is correct. If it's not, let the venue know and refuse to play. While that's painful, it's a lot less painful than a trip to the emergency room.

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  • While that sounds like good advice I don't think you understood what I mean by 'internal fuse'. The amp in question is a marshall tube reissue, there is a normal 2amp mains fuse in the back located next to the power input. it is accessible from the outside via a small plastic screw, which is how we know it blew. As I said in my comment on the original post, it is being serviced by a tech to fix and check for problems - the reason why the amp blew is off topic. Nobody is modding anything. Changing fuses in 3 pin power leads isn't tampering or unsafe. Please read my comment on the OP. – jammypeach Sep 24 '12 at 9:28
  • Point taken, but I then I don't understand what you are specifically asking. What do you mean by "fuse the power leads". Where exactly do you want to put a fuse and what does it connect to on either end ? – Hilmar Sep 24 '12 at 14:53
  • I assume things might be different over the pond (I'm in UK) but the leads that supply power to the amplifier all have their own fuses. normally they are household 13 amp fuses - it occurs to me that this will let through enough of a surge to blow the 2 amp mains fuse on the amplifier. does that make sense? – jammypeach Sep 24 '12 at 14:54
  • so I'm thinking if I replace those with 2amp fuses, it might offer some protection and be easier to swap out. Ofcourse I take your point about dodgy power outlets, this was probably what caused the problem to begin with. – jammypeach Sep 24 '12 at 14:55

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