Is the tone control on a Europa TG or TR variable? In other words, when you pull out the volume knob shouldn't you be able to increase/reduce the treble? Reason I ask - when I pull out the volume knob on my Europa TG the tone is at a fixed high treble and if I attempt to reduce the frequency (turn volume knob CCW) the treble remains constant while the volume reduces. Is this correct or have I got a bad potentiometer on my Europa TG? Ridiculous question I know, but it's been decades since I've operated a mono radio..and I'm not current