The PS-7 Power Supply may be susceptible to RF entering through the accessory 13.6 VDC phono jack in some station installations where this jack is used, such as when the SP-75 is plugged into this jack. It will cause the PS-7 protection circuit to activate, shutting down the power supply, or create power supply oscillations. 

To eliminate this, a .01 MFD / 600 V disc capacitor should be added from the tip of the 13.6 VDC accessory jack to ground. 

The later PS-7 power supply mounts the 13.6 VDC accessory jack into a printed circuit board. Since the board blocks access to the jack's ground lug, the ground lead of this .01 MFD disc capacitor should be connected to the ground foil of the circuit board. A small amount of spaghetti insulation should be used on the capacitor leads to prevent possible shorts.