Don't know what fuse your Engl uses, it should say on the back of the amp, but your local music shop should have some in. I bought a few the other week at 50p each for 2 mains & 2 HT (T2A 2amp & T500A 500amp).
If the mains fuse blows, you might need to take it to a tech to have a look at the power valves, if the fuse blows again, I think it might be an idea to have someone look at it.