A REAL GEM...SERIES 2 ACTIVE BOSE EQUALIZER FOR 901 SPEAKERS. COMES FROM MY DAD'S COLLECTION...SPEAKERS NEED REDONE ,SO LETTING THIS GO TO SOMEONE IN NEED...IN EXCELLENT CONDITION. I PLUGGED IT IN ...BUT HAVE NOT TESTED IT DUE TO THE 901'S NEEDING THE CONES REPLACED...HOWEVER ABOUT 8-9 YEARS AGO MY DAD HAD THEM ON DISPLAY AND WORKING WITH THE EQ...AND SOUNDING GREAT..BEFORE THEY WERE PUT AWAY IN ANOTHER ROOM TO STORE. The serial # is 118586.I UNDERSTAND CAN ALSO BE USED FOR SERIES ONE ALSO. THANKS AND GOOD LUCK!