Wireless has a point about the grid leak, however when I squint at the photo there is a resistor going from the socket to ground. Cannot quite see exactly where it is connected , its the red-orange-grey??. I can clearly see the 47ohm stopper, that ?? resistor could be the leak?

The 2A fuse is in the right place for when the crappy on/off switch block arcs over short circuit and sets the wiring and cord alight.
It has nothing to do with protecting any transformer, just there to prevent the house burning down!
I have had more than one of those things fail and blow the fuse.
I place a fuse there in all my new builds because I have been there and done that.
Fred.

" the crappy on/off switch"

I have just received back a love job where the on/off switch in the tone control failed. Luckily no fireworks, but there could have been. Will have to consider a mains fuse.

As noted and there is a photo of it on the forum. The Transformer melted down secondary side & could have easily started a fire. Luckily the owner was using the unit at the time. As said fuse did not blow.

Dodgy stuff here trips the RCD's & when the fuse box had none, the bench did. As that set has back bias that's the ideal spot for protecting things secondary side as well. The bench PSU is fused both sides as its chances of being presented with a fault are very high.