Help with biasing vintage V35 Audio Research amo

So the unit came with KT90 tubes which are set nominally to 75mA from the factory. When biasing I’m suppose to adjust for an average reading of 37.5mVDC.

if you change a resistor to a 100k ohm resistor next to the bias adjust aDjustment I can use 6550 tubes, per the manual. I changed the resistor, however, the manual doesn’t say what to adjust these tubes to.

any suggestions what the bias should be adjusted to?