[Amps] grid fuses

[Tom W8JI]

>>So the grid instantly cools, all leakage currents or arcs 
>>to
>>the anode vanish, and the grid remains at zero volts at 
>>the
>>instant of grid opening.
>>
>>Is that what you are proposing?.
>
>
> If the grid to ground circuit is open (fuse or resistor 
> blown open), it is impossible for the anode to arc to the 
> grid.

It is already arcing. That is what makes the resistor fail.

>It's impossible for any open circuit to carry current 
>unless it was to arc across the break. In this case, it 
>would have to arc
> between the blown fuse caps or resistor ends to ground (I 
> doubt there would be much left to arc).

You can doubt it, but if you start an arc with 50 volts the 
lead can pull back 1/4 inch and still maintain the arc 
through plasma. With 3000 volts it is quite easy to sustain 
an arc for a few inches. I suppose people don't think about 
this much, but that is why high voltage fuses are filled 
with "sand" and have an element several inches long. Anyone 
who thinks a 1/4 watt resistor will quench  an arc needs to 
spend some time doing HV experiments.

> I also highly doubt the
> whole grid getting real hot from the initial arc that 
> opens the fuse since it's a very fast occurance.

You are mixing examples. I clearly separated the two forms 
of grid current. Please reread carefully. I never said the 
arc heated the entire grid, although it will cause plasma 
inside the tube and that certainly will instantly heat the 
area where the arc is.

What I actually said is there are TWO distinct sources of 
excessive grid current. One a tube HV fault to the grid. The 
other an electron bombardment (kinetic energy) problem from 
excessive grid current.

This isn't as complex as it is being made.

73 Tom