[old_tv_nut]

A slight correction - the Trinitron fine horizontal wires were added to reduce vibration of the vertical wires, not to alleviate effects of heating. The Trinitron vertical wires were under tension until heated very excessively, which normally could not happen with the current densities that could be reached in a normal chassis design. Edit: on large Trinitron tubes, knocking on the face would vibrate the grille, and you could plainly see the effects of the grille wires ringing.

Self-supporting shadow masks were subject to local expansion if there was too much local current, like the white patch in composite color bars/white/I/Q pattern. This could not happen with the Trinitron tensioned grille or the later Zenith flat tension mask tube. Self-supporting masks also were subject to overall expansion due to average temperature, and mounting techniques were developed that moved the mask closer to the phosphor screen as it warmed up and expanded over-all, thus maintaining design aim-point beam landing and good purity.