your Bias depends on your plate voltage ..... and then where do you want to run them .....
I always go with 70 % ....
can't go wrong with this simple vid from Eurotubes
it looks like someone had put a resistor over at least one of those .... most likely to bring the voltage where they could bias EL34's or vice a versa .... if it was originally running EL34's .... they did it to bias the 6550's