I'm assuming the .5A fuse is for the screen supply of the tube amp in which case I might use a ceramic fuse vs. a glass fuse as glass fuses can shatter. Any properly rated fuse holder i.e. from Littlefuse etc. should work fine unless the amp uses the KTK type large fuse. I don't believe they do. It's been a long times since I worked on one. Whatever fuse holder you use just make sure it's free of corrosion.
