How to add sound to amateur films (1954)

For every pick-up, there is a correct distance d at which the pivot must be set from the turntable centre (left). If you mount two turntables (right) so that the spacing S is less than twice d, you can mount a pick-up to operate on either turntable. From each centre, draw an arc of radius d. The points X and Y where they cross are suitable centres for your pick-up pivots. fit the motors to a single piece of seven-ply. Should a defect arise, however, it is useful to be able to inspect each motor separately. Best of all, then, mount the motors and pick-ups on a new seven-ply board and screw it to the frame temporarily. Then remove it and cut it into separate boards for each motor and each pick-up. When you screw the four pieces on to the frame once more, the screw holes already made ensure a neatly lined up job. The rest of the case you make by covering the lxl inch framing with hardboard or three-ply. This withstands hard wear, yet is light enough to be portable. When mounting the pick-ups, see that they are pivoted at the correct distance from the turntable centre. With a new pick-up, this important dimension is usually specified, or a template is provided. In re-mounting an existing record player, carefully repeat the original spacing. Generally the stylus of the pick-up should over-swing the turntable centre by about £ inch to provide good tracking. That is, the stylus should always be trailing as nearly as possible along the groove, not obliquely to it. If you want to be able to use one pick-up on both turntables, mount it at the correct distance from both centres. Suppose you know that it should be mounted at 25