• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Filament bias safety

What's the correlation between this two things?
If no filament (regulator goes to ruin, resistor breaking, filament burns out), the DH tube halting to conduct.

Only the DC coupled power tube grid may be a problem (if it wasn't the tube defected).

BTW I always use fuse in B+.... but in these cases this doesn't help.
 
In the case of self-bias, cathode resistor is often in the range of 750 ohm or more. This provides a self-protection mechanism.

In filament bias, the filament resistor is much smaller. Hence I am wondering - any protection mechanism to keep in mind when implementing filament bias