[HAM] Adding fuse protection to the 6X4 valve in the AO28 in order to protect the transformer from a heater to cathode short circuit.

[Kon Zissis]

Hi everyone.
As I mentioned the day before , I have added  four fuses into the AO28
preamp of my 1965 C3.
I added a fuse  between the anode pin 1 of the 6X4 and the corresponding
wire of the 340 volt  winding of the power transformer .
 
The 6X4 has two anodes (  pins 1 and 6 ) so therefore I am wondering if
I should also add a fuse between the anode pin 6 and the corresponding
wire from the other 340 volt winding of the power transformer so that
the power transformer is better protected  if the 6X4 valve develops a
cathode to heater short circuit. 
 
What are the correct  fuse ampere ratings and the fuse type ( fast blow
or slow blow ) to protect the power transformer  from a 6X4 that
develops a heater to cathode short circuit ?
 
The AO28 schematic says "50 MA" next to the ground wire coming from the
centre tap of the HT voltage  secondary winding of the power transformer
so therefore would 100 mA or 200 mA fuses be OK here ?
 
Thank you in advance for a reply.
All the best.
Kon