I think it’ll be 2A at 120V, 1A at 240V.Just double checking here - the amp panel on my JMP 50 says 2 amp fuse, but I should be using a 4 amp fuse since my mains voltage is 120v, correct?
What's the voltage rating for the 2A fuse? Typically if the voltage doubles the fuse rating is halved.
Ok. I see that. Also, this schematic shows a 2A fuse with the voltage selector on 120.I think it’ll be 2A at 120V, 1A at 240V.
Exactly. What I meant to say, and admittedly wasn't clear, was what is the voltage rating on the amp, not the fuse. I understand that the fuse rating is max for the fuse, and that amp amp running 120v is pulling 2x the current as an amp from Europe running 240v. My bad.It has nothing to do with the voltage rating. A fully functioning amp will draw half as much current off the mains if they are 240v vs 120v. Therefore, to get the same protection, you need a fuse that has half the CURRENT rating for 240 volt mains vs 120v mains.
You could use the same fuse, but there will be less protection provided. Going the other way, from 240v to 120 you have to double the fuse current rating or it will blow on you. It's best to use the proper current rated fuse for the mains voltage you are using. The things are cheap, so do it right!
The voltage rating can be anything higher than the wall voltage you are using. So, at least 125 in the US and at least 250 in much of the rest of the world.
I just got done working out the amp for 30 minutes at full blast with a 2A fuse. No issues so far. I wonder why the tech that went over this amp before I bought it had it fitted with a 4A fuse?Bear in mind that IEC fuse types are specified differently to UL.
Being in North American, I expect you’ll find UL fuses a lot easier than IEC, the latter being what Marshall will probably have used.
Hence 2A sloblo may not cope, you may need to increase the value to 2.5A or 3A sloblo.
See https://dalmura.com.au/static/Valve amp fusing.pdf
The slow blow fuses filament is usually wound around a fiberglass rod. This is slow blow. Fast blow have a single wire filament that is straight not wound.Sure. My main concern is that I’m not sure the Bussmans I have are slow blow. The package they came in didn’t say so.