When the radar is transmitting the tuning bar intermittenly goes off and the display disappears for a rotation or two. This seems to happen only on the lower range settings. ( 1/4 mi to 1 1/2 mi. 2 mi and up it is fine ) I don't suspect the magnatron because the gain knob is in the same position as always and I can still see targets clearly at the 24 and 36 mi ranges. This is a automatic tuning radar and has no adjustable tuning.