Quote:
Originally Posted by old_tv_nut
It should be easy to check the coils for opens and also check that the connection to the sharpness control is not open.
BTW, I'm scratching my head about how that sharpness control is supposed to work. Where does the luminance signal go next (which tube and what electrode of that tube)?
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The 6LM8 acts as a cathode follower for the luma signal. So luma is output from its cathode and that is input to another luma amplifier. Dialing up the sharpness pot decreases the load resistance of the cathode follower amplifier which reduces its gain but increases its bandwidth.
I will clean the pot. While I am at it, I will try a few alternative tubes. Even though my NOS 6LM8 tests good… in the chassis performance can still vary.