From 1956 DeSoto Service Manual, Accessories section:
Open the door, and pull outward on unit until it contacts the stop. Push up the control (Red) knob from "Radio" to "Phono" position. Place record on turntable, and push down gently on red tab located on left side of tone arm. While pushing down on tab, move the arm to the right until it contacts the stop. Release the tab, and stylus (needle) will come to rest on the record player.
To prevent damage to the records (particularly in hot weather), remove the records from the turntable and place in the storage space. Pressure plate on bottom of storage space rises and holds the records firmly in place between the two flat surfaces when unit is pushed back into case. (IMPORTANT: Always place tone arm in "off" position when Hi-Fi unit is not in use.
Remove the vibrator from the left rear. Remove the four screws from the left side of the housing and the one at the rear of the housing; also, release the grommet on plug wire. Release the stop on the bottom of the chassis until there is sufficient room to remove the ground wire on the underside of the s1ide tray. Remove the turntable chassis from housing slowly, feeding cable assembly through housing to allow power chassis to be removed with the turntable chassis.