The solution to this problem is a perfect example of how an amplifier's safety can be increased at no cost to performance. By simply rewiring the power supply fuse topology, the amplifier can be made safer. Let's look at the first fault condition, the one where only the top fuse blows. If the current source is made to rely on the positive rail voltage to work, then it will turnoff when the top fuse blows. The voltage divider that feeds the bottom MOSFET's gate must be referenced to the positive rail and not to ground, so that when the top fuse blows, the gate voltage collapses. (The capacitor will slowly discharge through the bottom resistor, but not slow enough not to damage most speakers.)

    Like the case of the MOSFET current source, the biasing of the bottom tube must be referenced to the positive rail and not to either ground or to the negative rail. The circuit is only slightly altered to have resistor R1 attach to the positive rail after the fuse and resistor R2 attach to the negative rail before the fuse. Now if the fuse blows, the negative bias voltage will plummet on the bottom tube's grid.

    Now for the case where only the bottom fuse blows. We must keep the Op-Amp from losing either rail voltage when a fuse blows. This is accomplished when its power supply leads are attached to the other side of the fuses. Now if the bottom fuse blows, the Op-Amp still works to keep the top MOSFET from straying from ground potential.
    Futterman type (totem pole arrangement) OTL tube amplifiers can benefit from the same careful design choices. Both top and bottom tubes must stop conducting when either top or bottom fuse blows. Starting at the bottom once again, when the top fuse blows, the bottom tube must see a much more negative grid voltage.