Channel Imbalance Mystery

I’ve been experiencing a channel imbalance for awhile now that I cannot seem to solve. I’m only running a turn table so I cannot troubleshoot with a digital source. I have ruled out the TT and cart as the problem because I had it tested in another system and it sounds great there. I’m running a Herron VTPH-2A phono pre into a Cronus Magnum II integrated amp with brand new KT120 power tubes. (The imbalance was present with older power tubes too). My channel imbalance is left leaning. When I swap the tt inputs into the Herron preamp the imbalance is fixed. Vocals are dead center but my stereo orientation is flipped. No problem, just swap my preamp outputs to get me back to the correct channel orientation but doing so shifts the center image back to the left a bit but soundstage is correct. It’s not nearly as bad as when my tt inputs were in the correct L/R positions. What the hell is causing this?! I’ve tried different interconnect cables with the same results so I don’t think it’s a cable issue. Could it be unmatched signal tubes in the Herron? Signal tubes in the integrated? Super frustrated. Thanks for any help.