A couple of comments. First, the only way I know of that a fuze can effect the bias is if it has a high enough resistance to cut the voltage from the power supply. It seems unlikely that a fuze would reduce the bias by over 25%. Something else is going on here.
Second, the MK II has 2 trim pots that need to be adjusted to set the bias, and it is an iterative process. Did you adjust both? Here is a link to an excellent treatise on how to bias this amp.
http://mycollins.net/audio/artube1.html
Since you are familiar with biasing, you probably know this already, but I put it here in case others may need it.
Third, I agree that you should not use a fuze of higher value than the manufacturer recommends, even though it is only marginally higher and would probably still protect the amp. The risk is just not worth it.
Second, the MK II has 2 trim pots that need to be adjusted to set the bias, and it is an iterative process. Did you adjust both? Here is a link to an excellent treatise on how to bias this amp.
http://mycollins.net/audio/artube1.html
Since you are familiar with biasing, you probably know this already, but I put it here in case others may need it.
Third, I agree that you should not use a fuze of higher value than the manufacturer recommends, even though it is only marginally higher and would probably still protect the amp. The risk is just not worth it.