The KEF T27 Tweeter
Both the early 15 ohm and the 11 ohm LS3/5A used the KEF T27 Type SP1032 tweeter. NB. The earlier LS3/5 (without the A) used the T27 A6340.
The commonest problem found is an open circuit T27. In this case the only practical solution is to replace the unit. Although KEF no longer make the unit, Falcon Acoustics can supply new full specification T27s. Or you could take a chance with a secondhand T27 pulled from another KEF loudspeaker.
The T27 has a square felt surround to prevent interference effects associated with the cabinet edges and the tweeter dome is covered with a metal grille for protection which was sourced from a Celestion HF2000. This grille has a small effect on the frequency response which was considered beneficial as it raised the output a high frequencies. In some cases this may have been removed by an owner wishing to “improve” the speaker. The grille is fixed with contact adhesive.