This involves working inside a hot chassis so I use an isolation transformer and work one-handed. Always. However, I'd like to know how others go about this. I noticed that in the documentation for my NC183D the voltages are drawn on a diagram that matches the view with the receiver upside down on the bench. I prefer to work with the receiver standing up on its back, and I've built a small frame or dolly that allows this. However, the drawing showing the socket voltages is now rotated 180 degrees, which promotes confusion. Is there a better or a safer way? Can voltages be measured from the top of the chassis using tube extenders?
-DS

Sometimes yes, you can measure from the top with extenders. Some tubes and circuits act differently though when using an extender.
Converter tubes sometimes won't oscillate due to extra capacitance of the extenders.
Tubes using shields present a problem too.

I use extenders mostly for quick checks on a single tube or two.

For extensive testing I work with the chassis upside down.
If a reading is off, you then need to follow previous parts on the schematic and you can do this only upside down
I often draw diagrams showing chassis upside down with socket orientation relative to the other major parts, then transfer voltage measurements from the provided charts to the correct pin. No confusion this way.