The tube driving the Y shift is V2, more specifically the pentode on said tube. With the help of a resistor divider made with R10 (kinda), P3 and R14||R15. P3 is the Y shift dial, and they drive the grid of the pentode of V2. At first glance I was shocked for the high value of R10. In VCC I have 440V and after that resistor, in test point 23 I had 40V. Just so teh grid coould get a higher voltage, I put a 680k reisstor in parallel with R10, rising the voltage to 60V, and voilà, Y shift was working "again". That is strange, no matter how you look at it. I think it has to do with that resistor in paralel with R15. It dosen't look original, could be a mod from the previous owner? A weird mod if you ask me.