I have a fender bassman 410. It's not working at the moment but I'd like it to be operable again. The "L-pad" has gone out on it and I have no idea how to search for a replacement part for it. I've tried searching L-pad on google and it renders nothing. I don't know what that proper terminology is so I don't know what to search for. It's the part that has the tweeter knob on it. Can anyone help please? Thank you much!