A tandem sub for a perforating gun system includes a tubular housing including a longitudinal first end, a longitudinal second end opposite the first end, a central passage defined by an inner surface, an electrical pass-thru assembly including an electrically conductive signal bar having a longitudinal first end defining a first electrical contact of the tandem sub, and a longitudinal second end opposite the first end and defining a second electrical contact of the tandem sub that is longitudinally opposite and electrically connected to the first electrical contact, wherein the signal bar is rigid along the entire longitudinal length thereof extending from the first end to the second end, and wherein the signal bar is coupled to the housing and a central axis of the central passage of the housing intersects the signal bar.