What model ARC amp do you have? The VT series therein, VT50, VT100, VT100 MK 2 series requires the 6922 signal tubes must also be biased.
I believe, looking at the schematic diagram for the ARC CA50, the 6922 tubes also require biasing. Especially the 6922 driver tube.
The 6922 input and driver tube must be closely, tightly, matched. Especially each section of the driver tube. If each section of the input and driver tube are not tightly matched you will not be able to bias the tubes to meet the required ARC specs.
https://www.arcdb.ws/Database/CA50/ARC_CA50_schematic_and_parts_list.pdf