A tremolo block combines a guitar tremolo arm with a cam locking mechanism so that when the arm is swung to a position for actuating the tremolo the locking pin on the cam is away from a mating socket or receiver, but when the arm is swung the other way, the cam pushes the pin into the locking socket so the tremolo is inactive and the string tension does not change. The position of the receiver or socket can be easily adjusted by the guitarist so that the string tension when the bridge is floating matches the string tension (and tuning) when the bridge is locked.