[Amps] Purpose of cathode resistor?

[TexasRF@aol.com]

If the fuse blows, the cathode voltage can rise to near the plate  potential. 
Most tubes will arc from cathode to filament or grid with this much  voltage 
present. This is not good for the tube!
 
The resistor can be much higher value than 250 ohms to perform the  
protection you want/need.
 
73,
Gerald K5GW
 
 
In a message dated 12/28/2005 10:41:47 A.M. Central Standard Time,  
dezrat1242 at ispwest.com writes:

I have a  question for all the amplifier experts out there.

In this  schematic:

http://members.ispwest.com/dezrat1242/cathode.jpg

there  is a 250 ohm resistor connected across the fuse/zener. What is 
the purpose  of that resistor, and why is that particular value 
chosen? (I have also  seen 200 ohms used.)

I can think of two possible reasons, but I'd like  to hear from the pros.

Thanks in advance,

73, Bill  W6WRT

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