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The ringing is probably mechanical vibration of the ferrite core of the flyback. It's usually curable by tightening those two nuts on the big C clamp that goes around the core (not too tight as the core can crack easily).
Your HV rectifier tube is good (if it was weak the raster would 'bloom' and fade out when you turn up the briteness).
The blue arcing when you touch the screwdriver to the glass and top cap of the HV rect is quite normal.
Insufficient height is usually a bad electrolytic coming off the cathode of the vert.output tube (although GE portacolors might not have this cap; other more knowledgable folks will chime in).
Last edited by old_coot88; 11-09-2019 at 05:46 PM.
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