Volume Level

Could be the setting of the antiskate. Could be other things, but I have forgotten them. Good luck.

Unless you were playing a mono LP it may mean nothing.

It could well be a tube in the phono pre- try switching the tubes from left to right etc and see if the imbalance changes.

Does this consistently happen on every record? It could be your cartridge alignment, tracking force, or antiskate as mentioned above. It could even be an issue with the cartidge itself. You may want to look at the documentation for your cartridge and arm to make sure everything is set up correctly. I should probably don my flame retardant suit before saying this, but this is one reason why I love having a preamp with balance controls.

If swapping tubes doesn't produce results then check cartridge alignment. See if you can find the image by moving to the left from your listening position. If it seems to be there but a foot or so off center you should be able to adjust this back to center. Find the azimuth adjustment on your tonearm, try making small adjustments and then listen for the change. You should be able to pull the image to the center this way.