Black matrix delta tubes were invented by Zenith & came out @1968.
They were called Chromacolor. They started on high end consoles.
14", 16", 19" 23", & 25" were built. Improved with smaller dots,
more HV, flatter & more square tube over the years.
@1976 Zenith came out with another new tube. The EFL " Extended Field Lens"
or Tri Focus. Deltas got phased out over the next few yrs. EFL came
in 13", 17", 19", 23" & 25" The EFL was an in line gun & phased out @1981
Zeno
