By the way, NEVER use a resistor to protect sensitive
Fuses are bad enough. They have a very slow failure period
as they melt and then open. The time is also dependent on
temperature and even the age of the fuse, but it can be a
very long time at 200% overload.
The grid often will protect a fuse, rather than a fuse
protecting a grid.
Anyone who understands anything about resistors would also
know a metal film resistor can take a pretty severe overload
before opening. It isn't anywhere remotely as good as a
fuse, and fuses are bad enough that they should be avoided.
The best system without any question is a solid state system
that drives a fast relay. Instead of a dozen seconds it can
open in a dozen milliseconds or faster, and the cut out
point is very well defined.
There are many more good and easily verified or common sense
reasons to avoid a fuse or worse yet a resistor for grid
protection, but the fact the tube would have virtually no
protection under most overload conditions is probably good
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