Mazda 6fq7 in Line Stage Shuts Down Tube

When I insert this tube in the line stage in my CJ PV9a it shuts down the other 6fq7 which is strangely enough in the phono stage.

Has anyone experienced this? The Mazda which is a Brimar made in England is a very good sounding tube if it wasnt for it shutting down the tube in the phono stage I would have to say it is the best sounding tube I have ever heard in a preamp.

Can someone help?