To do this test, be sure you have the screen voltage presence and the heater is lighted and HV is present.
Take a resistor 12K by 3 watt (you can salvage this from an old CRT tube.
Solder both ends on the resistor to a wire with crocodile clip as shown here below.
To test if the tube is good or not just clip one end of this gadget you have just made to the cold ground of the TV and the other end to each RGB cathode pins separately.
If you get all the three colors appear with the same intensity then you can assume the tube is good.
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