Bearings

[Al Skierkiewicz]

The original quad video tape recorders used from the fifties through the seventies used air bearings on the video heads and occasionally in other places. The head motor (about 10" long and close to 10lbs. of metal) required 12-15 PSI (I am trying to remember what the low side regulator was set for) to run the video head motor. There was a bearing surface at each and and a thrust bearing behind the head wheel. (the rotating disk that held the video heads) The pressure had to be applied first before power to the motor was allowed to be turned on. (the motor wouldn't even turn without air on it.) The motor ran at 15,000 RPM and was speed and phase controlled to record and playback video. Each of four video heads recorded one line of video across a two inch tape. (Unlike the helical scan machines today that scan almost lengthwise on the tape.) The only friction involved was the friction with a jewel tipped screw which set the stop for the motor shaft and the drag encountered by the head wheel turning so fast in the air. In addition the tape had to run in a vacuum "shoe" to keep it from getting eaten by the video heads. If you lost vacuum there was a distinctive high pitched squeel just before your tape got cut in two and little particles of mylar and iron powder erupted into the air.