Bulked and crimped yarn is produced by a device comprising yarn feed means arranged to form a yarn package, means for taking off yarn from an end of the package and heat exchanging means arranged to be in heat-exchanging relation with the yarn on its way to the package. Means capable of sensing the position of the take-off end of the package is arranged to send a control signal controlling operation of the heat exchanging means. The yarn feed means may be a fluid jet or feed nip rollers. A stuffer tube or a movable surface may be provided to receive the yarn package. The take-off position sensing means may be optical, electrical, acoustical, pneumatic, or mechanical.