“Center” of soundstage is left of center…

I think I’ve found the answer. I screwed up how I adjusted the tube bias Dow the mono locks. I had it totally wrong. Now all is well. Thanks everyone for humoring me.

Did this just happen one day when the previous day it was centered?

Lots of good comments. Could also be one speaker is slight forward of the other

I have this exact problem and tried many times to locate the source. After a few years I found out (hearing test) that I have a significant hearing loss in my right ear. It’s a fairly narrow bandwidth, but I barely hear anything in that band. It’s the root of my tinnitus. Music that’s engineered with instruments panned wide left/right is fine, but anything subtle has a distinct left of center image. 

OP:

Yes. If the problem persists after swapping inputs, the next thing to do is swap amp outputs. If the problem persists then it’s either the speakers, the room or your hearing. :)

I’m reversing the power amp inputs now. I played some cds and the problem was still there so the phone pre doesn’t seem to be the issue. If the proble migrates to the right side after I’ve reversed the power amp inputs then it must be the pre(?).

Have you tried reversing the left and right speaker outputs to see if the problem is with your equipment or your ears? No offense intended! If the center changes to the opposite side, you likely have an equipment issue.

Are the left and right sides of your room acoustically the same as far as symmetry, dampening, reflective surfaces, furniture etc.

Is this a new problem? Have you changed anything recently?

Have you tried another source?

Does it happen with all recordings?

Do you have a decibel meter that you can test the output levels with while playing pink noise to see if both channels read equally?

Have you tried unplugging and re-plugging the cartridge connections and all other connections making sure they are snug?  Have you reversed the connections to see if the center moves to the opposite side.

You could try reversing the left and right connections of each component one at a time and try to isolate the problem.

Too vague of a question to pinpoint, but these are my suggestions.