If measuring the voltage between the cathode and the grid you need to be aware of the loading effect of the meter, especially with an analog or some of the cheapo DMM's.
Scenario....The chassis to cathode voltage across a 100 ohm resistor is actually say 4.5 volts, but you measure between cathode and grid with a DMM that has a 1meg input resistance, the grid return resistor is say 680k, the voltage indicated will be approx. 2.69 volts (bad enough) With a 20kohm per volt analog meter set to the 25 volt range and measuring between the same two points the voltage indicated will be approx. 1.9 volts
With the same meter set to the 10 volt range the voltage indicated will be approx. 1 volt
In reality the actual voltage at the grid would be 4.5 volts....
All circuits are potential dividers:
https://www.electronics2000.co.uk/ca...calculator.php
Lawrence.