Marshall Fuse Value Question

[PDC]

So, I have a pair of 50 Watt Splawns and a pair of Metropoulos 1959 builds, all 4 of which use a 1-Amp 250v Slo-Blo for the HT and a 4-Amp 250v Slo-Blo for the Mains. I recently re-acquired my old '73 Marshall from a good friend and it is stamped on the back of the chassis for a .5 Amp HT and a 3 Amp Mains fuse.

1-HT and 4-Mains seems SO common, is there really something different about the circuitry in that old '73 that requires the lower value fuses? Or could I safely replace the HT fuse with a 1 Amp and the Mains with a 4 Amp like practically every other amp in existence??

 

[SpiderWars]

Is that what are actually in the '73? I'm wondering if the values stamped on the back of the '73 are for 220v operation? I'm just guessing but I would think a 0.5A HT fuse in a 100W would nuisance blow at some point.

 

[PDC]

I can’t think a 1 Amp HT fuse would allow anything terrible to happen …