G2 protection Voltage comparator circuit

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Hi,

I wonder if any of you guys are handy around voltage comparator circuits? What I want to do is to protect G2 (the sceen grid) in a pentode CCS config at the tail of a triode cathode follower. If the triode (upper tube) goes south, looses contact or something, the anode of the lower CCS pentode tube is not taking the current and the weaker G2 gets to take the full current, which will smoke it. Classic problem.

So my idea is to create some protection circuit that only closes the G2 feeding if the triode CF is in place working. The usual way to solve this is to put a big current limiting resistor on G2 but that is also very contra productive to functionality. G2 should have a low Z supply to work properly.

My idea is to put a voltage comparator circuit over the cathode resistor that only closes the G2 supply line if there is voltage over the resistor. The thing is:

1: I have no experience of those components/circuits and googling (or goofing) didnt get me much results for the appliance.

2: I dont want to interfere with the functionality of the cathode resistor. The comparator can not be shorting it, disturbing it with capacistance etc.

Any tips, scetches, anything would be appreciated.

Cheers
 

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If the anode voltage of the pentode doesn't drop below the g2 voltage you can do it simply like this (bestpentode).
In case of an interrupted anode current the g2 current is limited to the base current of the transistor.
Mona
 

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