tube testing question

6BJ6 and 19T8 are tubes used in FM table radios. Do you have any others you could test for comparison? That could be helpful.
73, Rod WB6FBF

1-What kind of tube tester? 
2-Brand Name? 
3-Model Number?
4-Have you had a calibration of the tester done?

If it flutters then It may be a capacitor is breaking down, Some testers only use AC throughout for tube testing. Others have an actual Amplifier which has DC. (more Expensive types).
Does it have only one meter OR UP TO  3?
You might be getting some tube breakdown, which is unlikely. Or if it uses selenium diode stack It could be on the verge of failure.
Have you checked the transformer(s)?
Does the tube tester have capacitors ?
Have you tested the voltages? See if the tube manual shows maximum Voltages at each of the tube pins.
Check to see for solder connections being correctly soldered, (no Cold Solder Joints.)
Clean each of the Switches and Pots.

Good day
I have tested two tubes (6BJ6 & 19T8) and when the needle gets to the top end it starts to flutter back and forth about 3/8th 0f an inch. This has never happened before. I have tested other tubes before and after this with no problem.
Your thoughts.

Ken