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

[Peter Chadwick]

>>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

So if it doesn't matter, why do tube manufacturers specify a maximum grid - cathode resistance for a lot of tubes? Even low power audio tubes used in Class A?
My experience is that exceeding the the maximum grid-cathode resistance can (but not always does) lead to a plate current runaway, even in tubes with no measurable gas (as measured by grid current)
73
Peter G3RZP