The knurled brass adjusting screw at the left rear of the chassis controls the inter-station noise-suppression feature. (This applies to the Code 121 and 122 Model 16 only). This screw [variable resistor] controls the sensitivity of the receiver at which the automatic volume control begins to function. At the time of adjustment, the screw should be turned in a counter-clockwise direction until the best average reception is obtained with a minimum of inter-station background noise for the particular location in which the receiver is operated.
The switch on the side of the cabinet should be in the UP position when the above adjustment is made. When the switch is in the DOWN position, the quiet automatic volume control [QAVC] feature is eliminated and the maximum sensitivity is available at all times. It is sometimes desirable, when tuning in distant stations, to place the switch in the DOWN position temporarily.
From the Philco Serviceman – August, 1933.