I skipped to page 48(GB) and see no support for any HD signals. So for all intent and according to what I read you have the classic old standard definition display.
I see no support for HDMI or digital signals so before you spend money on any convertors let's see if the DirectTV receiver number can be shared to see if it supports any signal this TV has.
-> I see this is one power hungry TV at 360 to 400 Watts. Most sets in this range today are under 100 Watts.