Tape cassette

A tape cassette, comprising a housing accommodating a magnetic tape, said housing having a window on one of its sides;

• guiding means including two tape reels rotatably mounted in said housing and adapted to alternately wind and unwind the tape, and a plurality of guide rollers fixedly mounted in said housing and adapted to guide the tape with a predetermined speed in a predetermined path between said reels when the tape is in its working position in a tape recorder;
• and stroboscope means mounted in said housing and comprising a shaft rotatably supported in said shaft and a stroboscope disc secured to said housing, said tape being arranged to at least partially engage said shaft to move over said shaft in said predetermined path, said stroboscope disc being mounted in the housing so that at least a portion thereof is visible through said window whereby any deviation from said predetermined speed of said tape is indicated in said window, at least a pair of guide rollers being formed with a plurality of alternating ribs and grooves extending transverse to the direction of movement of the tape and providing means thereby adapted to contact the tape for retarding the tape in its movement in said working position.