1956 Wurlitzer

Hello all!
I have a beautiful 1956 Centennial Wurlitzer.....

Due to robustness / inconsistency I recently had the amplifier rebuilt. This sorted the issues but has left the machine with 2 differences:
1. The volume control is not linear in that all the volume kicks in during the last 25% of the rotation
2. The ultimate amplification is lower ie the machine is quieter at full volume.

Any ideas anyone where I might go with this? The amplifier restorer says that the output signal is correct, I'm sure it is but these differences definitely exist now.

All help and your time much appreciated!
Paul