1968 Zenith 20Y1C50 chassis - advice needed

[joe111671]

Here's what I found so far. The focus voltage comes up to 4KV, and does not drop at all as the set goes out of focus. If it does, it's not enough to register on my probe.

There's a bit of hissing in the HV cage that quiets down after a bit but never goes away, but I couldn't see any arcing anywhere with the room completely dark. I'll try to figure out some "stethoscope" way of pinpointing where that hissing is coming from.

What I did notice is that the shunt regulator tube has a bit of blue glowing, it can barely be seen at the top right of the picture. I put a picture of the same area with the lights on for context. I don't know what the shunt tube does, but wanted to mention it since I saw it. I recall seeing something about gassy tubes glowing blue.