[Amps] grid fuses

[Joe Subich, W4TV]

Lon W. Cottingham writes: 

> but why pay $200 ++  for a 3-500Z when a 6 cent, 1/4 watt resistor, 
> can/will save them from certain demise from several very common 
> faults?

If fusing the grid is so "safe" why is it not used in commercial 
transmitters?  If it protects a tube so well, why has no tube 
manufacturer recommended it (they recommend a surge limiting resistor
in the anode circuit)?  

I have worked on many commercial and broadcast transmitters over the 
past 30+ years and not one had any kind of grid fusing.  Every one of 
them had current limiting in the anode circuit and many had electronic 
"trips" that would dump the stored charge in the power supply (known 
as a "crowbar") in the event of a fault.  In fact, a "fuse" in the 
grid circuit is the opposite of what a qualified design engineer would 
use as it would keep the transmitter off the air until a maintenance 
person could physically strip down an amplifier to replace the fuse 
rather than simply reset/recycle when the fault clears. 

> I guess many of us are as blind and closed minded about amplifier 
> theory as we are about politics.  

As P. T. Barnum is credited with saying, "There is a fool born every 
minute."  It's those fools that keep snake oil salesmen and e-mail 
scammers in business.

73, 

   ... Joe, W4TV