[Amps] Grid fuses (was: Life and gain of 3-500Z)

[Tom W8JI]

>>If the tube is not gassy, and the grid is floating, the 
>>electron
>>stream from the cathode probably raises the grid-cathode 
>>(fil-CT)
>>potential to a few volts negative.

>I have observed this phenomenon in small receiving tubes 
>with the grid
>floating. No doubt it applies to their big brothers as 
>well.

Not quite Bill.

The very reason a tube flashes over in the first place is 
the anode has a conductive path to the closest element 
inside the tube, the grid.

If we allow the grid to rise by virtue of a fuse we then 
have the problem of the grid no longer shielding the cathode 
from the fault. We have a grid firmly nailed to the anode, 
and all the energy from the anode is available to dump 
across the small grid to cathode gap inside the tube.

There isn't any way that is even remotely a good idea.

73 Tom