This is what I've got:
From Paul, for the later amps with the led's, for initial startup. Power up 20 min. + Idling, no music playing, flick switches one at at time, adjust to fully light the second LED, with a hint of the third beginning to light. repeat checking till all read "2-1/2". Check after 1 month w/ new tubes, then every 6 mo.
I don't have and cannot find the instructions for the older version.
A survey of forums finds 350-370 on all four; another writes 650 mv for 6550 or KT88 and 350mv for EL-34.
I bought a bias meter kit for use between tubes and sockets, but I haven't tried it out. I intend to get a reading when the lights are consistent with the instructions, and if there seems to be consistency, I'll try to set to the values listed.
Other than the TAD instructions, all of this is a result of sleuthing, and I have no way to know if the information is acccurate or not!