A Fuse question

I just purchased a Magnum Dynalab Integrated Amp model #MD 308
I always check fuses for correct value before using.
This unit states on the back "3AG fuse " however it does not state the amperage
The fuse that is in it says : 250 v.... 4A
I checked manual to verify the correct fuse amperage is in it ( 4 amp ? ).....but manual does not 
indicate amperage!
Does anyone have this info I am seeking. 
Perhaps an owner of this amp could check and verify for me.
Thank you