Zenith Roundy Adjustment Issues.

[DaveWM]

yea so lack of height is the real issue, the linearity problem will likely resolve when you can set it correctly.

I would try in this order

check line voltage (should be at least 117ac)
check B+ voltage
if ok
try known good tubes in vert (multi and output)
if no change try each testing inbetween

check resistors mentioned esp the 48k or 68k from the boost to the height pot, this frequently drifts high.

check the screen and plate resistors per picards post

bridge the 100uf vert out cathode bypass

if still an issue comeback for more. My money is on the 100uf OR the boost resistor in series with the height pot. I would also recommend replacing the .1 elmenco's there are two of them, replace them both.

The pots could be bad but if the were I would think the adjustment would be jumpy and or not working. the best way to test a pot is to take it out of circuit and test with a analog meter. For now just hit them with some clean juice and work them some.