Advice Admiral 12X12 20Z1 low contrast w/ lines

[Electronic M]

Do you have video on the screen to tell if the raster is expanding when the brightness drops as you increase the brightness knob? If the raster is expanding (blooming is the correct term) then that means the brightness control is working but as the beam current increases with brightness setting the HV is loading down and sagging. If the HV is sagging your HV rect would be the likely cause but other horizontal issues are possible.