If the new tube does not reach the factory-recommended bias level, it means that the new tube is probably weak, has low Gm.
New KT88s come in a wide range of Gm, from 6000 to 8500.
Try to buy a matched pair around 8000 GM and 80 mA.
This is just a guess, I have no insider information about your amps.
New KT88s come in a wide range of Gm, from 6000 to 8500.
Try to buy a matched pair around 8000 GM and 80 mA.
This is just a guess, I have no insider information about your amps.