I am testing a few 6SJ6C tubes from an estate sale. They both test good but the meter pointer has a little flutter. I've seen this before but not sure if this is signs of a bad tube or what? Thanks
One possibility is that you have made an oscillator! You should be able to see this on a spectrum analyzer or hear it on a receiver.An oscillator requires an active element with gain to overcome the circuit losses. Only a good tube can do this.Normally there is enough resistive loading or losses to prevent this.