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[Amps] Grid protection resistors

To: "Amps Amps" <>
Subject: [Amps] Grid protection resistors
From: "Tom W8JI" <>
Date: Mon, 26 Jun 2006 16:46:57 -0400
List-post: <>
By the way, NEVER use a resistor to protect sensitive 
expensive devices.

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 

73 Tom 

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