[Amps] Purpose of cathode resistor?

[Phil Clements]

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Steve Thompson
> Sent: Wednesday, December 28, 2005 12:15 PM
> To: amps at contesting.com
> Subject: Re: [Amps] Purpose of cathode resistor?
> 
> 
> 
> TexasRF at aol.com wrote:
> >
> > If the fuse blows, the cathode voltage can rise to near the plate
> potential.
> That was my immediate thought, but won't the cathode stop rising once it
> reaches the tube's cut off bias?
> 

The 250 ohm resistor provides a total of 10,250 ohms cut-off bias if the
fuse blows. There is no path to B- when the fuse is open except the 250 ohm
resistor. The value is not critical as long as it does not affect the normal
operation of the zener.

((((73))))
Phil Clements, K5PC