FWIW, I found some good material on this subject in the
March 1960 QST, pps 33 - 38.

Another question: I've been told that the 6JH8 works best
with 0 volts on the deflector electrodes. However, it was
common practice with the 7360 to use a voltage divider
between the plate and deflector to provide negative feedback
(improved linearity) while biasing and balancing the
deflection electrodes. I'm thinking of using the same scheme
on the 6JH8, except having the low end of the voltage
dividers going to a negative bias source. That would allow
setting the electrode voltages to 0 volts, or slightly negative
or positive--whatever works best--while still keeping the
advantages of having negative feedback from the plate.
Is this worth doing?

Pete