Balance control?

The trim pots in the Herron might alter plate resistance on the input voltage amplifier tubes, which would affect gain. In my opinion most audiophiles would get in trouble fiddling with such a parameter. Or they may operate in some other way. Regardless, Atmasphere said all that needs to be said, to help the OP. I hope he is following the advice already given.

While extremes of azimuth adjustment do have an apparent effect on channel balance, the cure is worse than the disease, because the stylus tip will be at a suboptimal angle to the groove resulting in aberrant wear on both the stylus and your LPs and audible distortion as well. I advise against adjusting azimuth to cure channel imbalance.

It is unwise to judge channel balance based on “perfect” centering of a vocalist.  You have no idea what the sound engineer was after when he set up the recording session or what sort of mixing was done.  Very often, the vocalist appears to be standing just to the left of center, near to the piano, in a jazz recording.  With the bass, drums, and etc to the right or behind the vocalist.