My post didnt make it so I will do it again.
RTVNUT is 100% that the first system 3 was the best. Check
the model #. If it starts SK25?? or K25?? its the good one.
They only made them one year, the K line. Very robust
chassis & great pix. Only common problem was cold joints on
the hoz drive transformer, a few PS boards (24V reg) & 9-155-01
CRT boards.
9-160 sets were WAY over engineered in the PS & hoz.

They did introduce a comb filter on better models that made
a huge improvement in pix. Also you could get a real RATS.

Also the first Zenith monitor a 19" cube set with 2 seperate speakers
called "video high tech". Dont remember model # or year.
73 Zeno