Buffer position sensing and reel motor control for a magnetic tape transport

Claim 1

A BUFFER TAPE-LENGTH CONTROL FOR A DRIVE HAVING A PAIR OF TAPE BUFFER ARMS RESPECTIVELY ASSOCIATED WITH A PAIR OF TAPE REELS, EACH BUFFER ARM CONTROLLING A BUFFER LENGTH OF TAPE ADJACENT A TAPE PROCESSING STATION, EACH BUFFER ARM BEING MOVABLE BETWEEN TWO LIMITS RELATIVE TO SAID PROCESSING STATION, EACH BUFFER ARM HAVING ASSOCIATED WITH IT: AT LEAST A FIRST REED SWITCH AND A MAGNET ARRANGED FOR SWITCH ACTUATION BY BUFFER ARM MOVEMENT WITHIN SAID LIMITS, A REEL MOTOR FOR DRIVING EACH REEL, AND A CIRCUIT CONNECTING SAID REED SWITCH TO SAID REEL MOTOR FOR DRIVING IT IN A PARTICULAR DIRECTION TO CHANGE TAPE TENSION ON SAID BUFFER ARM WHEN THE BUFFER ARM MOVEMENT ACTUATES SAID REED SWITCH, SAID REED SWITCH INCLUDING FIRST AND SECOND CONTACT SETS, A SILICON CONTROLLED RECTIFIER PAIR HAVING A PAIR OF GATE ELECTRODES, AN ALTERNATING-CURRENT POWER SOURCE HAVING OPPOSITE TERMINALS RESPECTIVELY CONNECTED TO SAID GATE ELECTRODES IN SERIES WITH SAID FIRST AND SECOND CONTACT SETS.