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@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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