Canadian Marconi TV 102T17

[Electronic M]

Do you have a tube tester or a strong 6U8? Has the low voltage lytic on the detector been replaced in recent years?

Another option if you don't have a tester is to check voltages on the tube if the grid is normal or less negative (/more positive) but the plate is higher than normal that indicates a weak tube (DC plate current below normal).

There's also the lazy audiophool method of turn the set down, plug the audio output of your video source into your stereo and turn the stereo up....I tend to favor this even on sets with good sound.