you clip in an equivalent resistor across the plate and ground, then feed the output with your VNA. Tune for 50 ohms, and when you power it up, it will be close.
The important thing to remember is to remove the resistor when you’re done.
At least, be thankful you remembered to remove the VNA from the RF output! Easier to view a zorched resistor with humor!
When I am working on any of the high-voltage equipment, if the task requires several steps of disconnection or disassembly, as I proceed, I create a simple checklist, starting at the bottom of the page, working upward, listing each part that was disturbed. Then when I am ready to restore it to test status, I start at the top, and make sure I have left nothing in an unsafe condition.
It may be a sign of getting old, as I did not do this years ago. But if a checklist works for licensed pilots, both young and older, it can't be all bad. If I am too tired to go to the trouble of keeping the safety list, it is time to do something else!
