Take Herbert out of its Headshell. Install two adaptors of bias rite into those sockets which you want to bias:
A = 3 + 4 (inner pair) B = 2 + 5 (inbetweens) C = 1 + 6 (outer pair)
Put the tubes into the sockets/adaptor. Switch Herbert on, wait 30 seconds, flip standby switch. Read the mA on the Bias Rite. You should adjust each tube to get a reading on your bias rite of 35mA/tube. This is easy, if you have external bias pots (depends on model). Switch amp off. Uninstall adaptors, repeat for the other two sockets.
If you have only internal trimmers, do this:
To adjust the trimmer, locate it by flipping the amp upside down (use a set of thick books, you need to be able to have the adaptors and the tubes installed while the amp is flipped).
If the amp is safely standing, switch it on (adaptors installed into the correct sockets, also tubes in the adaptor), wait 30 sec, hit standby and read your Bias Rite.
Locate the corresponding bias trimmer (A, B, or C) inside your Herbert (pots facing you, amp flipped, leftt side, close to the midi chips). Turn the trimmer gently (!!!) until you get the desired reading.
Switch amp off and repeat procedure for the other pairs.