I have never heard of a "magnetron fuse". Fuses are easy to locate on microwaves, though. The easiest way is to follow the power cord from where it enters the oven's frame to where it terminates on the board. There is a fuse in the immediate vicinity of the termination. You can check the fuse with an ohmmeter...it should read zero ohms, anything else means the fuse is blown.
If your oven is blowing fuses that means there is something else wrong with it, most likely the magnetron. You can't miss the magnetron, it is mounted on the side of the cooking cavity, you can identify it by its heat fins. If you want you can trace the wires from the magnetron back to the board, there usually is no fuse in that line but a capacitor is always in that line. Check the capacitor as well, if reads zero ohms it is bad and it is what needs to be replaced.
I am curious as to what is going on with your oven. Do the lights and fans come on but it doesn't heat or is it completely dead, no lights, no display, nothing?
Either way, I am including a link for you to a site that has all the parts and accessories you need for your model microwave. I hope this helps, here is the link: http://www.espares.co.uk/parts/microwaves/neff/h5470n0gb%2f02/p/1095/1126/0/553422
on Dec 11, 2014