the only real way to find out is to test it on a crt testor,i have never seen a 10bp4 that has cathode drive from the video amp,drive from video usually goes to G1..
sometimes these old sets the cathode is grounded..
i would just test it.. and recap the set if you have not done so..
gain is almost always the contrast control in these old sets..
and it is possible to have an open cathode.. but testing would tell.
good luck!
terry