K4000 biasing problem

Hello, 1st time post, and a long time since I did a lot of electronics so please be gentle!

I bought a k4000 about 18 months ago, and it’s served well, until,
It burnt out R49 and took out the valve.
Have replaced r36 through 51 with 39ohm 1/2 watt as suggested and replaced the valves with
I can bias 1,2 and 4 but can’t get a reading on number 3.
Potentiometer has no effect, is it just a case of a bad potentiometer? I checked the boards and
Nothing else seems fried!