There's a third fuseholder under the two red wires at the top left that should hold a 250mAT fuse, the other two hold 2.5AT fuses. All are standard 20mm.
It looks like a simple enough job to replace the broken fuseholders. The PCB will have to come at least partly out to gain access to the underside but that shouldn't be too difficult. There's a service manual here that you might find useful... https://elektrotanya.com/warwick_hdb-electronic_tube-path_5.1_sch.pdf/download.html