Balance control?

@bimmerman2 

Awesome Keith did that! That's a great mod. I wish more preamps with analog volume controls would provide a few high quality (high quality resistors) discrete steps of ~ 1/3rd dB in each direction L/R. That should provide enough flexibility for most use cases (more than 1 - 1.5 dB cumulative imbalance and something is wrong) without a significant SQ penalty. 

It’s pretty slick he has that inside there, the range of adjustment isn’t huge by any means, but it was enough to balance out the very slight imbalance I was getting. Took forever to track down what it was, did all the steps above, cart good, cables good, speakers/room placement symmetrical to the 1/16th of an inch. That simple little tweak of the pots brought it into perfect focus.

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.