For what it's worth, I found this source:
ACK Birmingham
(800) 338-4218
Buss GDC-Type
1/10 (100mA)
250V
This is listed as a European type. Go figure. Anyhow, the fuses are in their catalog.
This is the fuse (three fuses, actually; F4, F5, F6) refered to on sheet 3 of 4 of the 300T schematic. These fuses are a trip line at the screen grids.
As for myself, I'm going to get a big handfull of these creepy little fuses. It can't hurt.
