Potentiometer "US 250KA" same as 250k?
It is a regular 250K ohm potentiometer but the "A" tells that it is logarithmic while the "B" tells that the potentiometer is linear. 

Now you have to know if your system needs a logarithmic potentiometer or a linear one.

Our ear perceive sound on a logarithmic scale so there are chances that you need a logarithmic one since you want to change the volume.